This PDF file contains the front matter associated with SPIE Proceedings Volume 7385, including the Title Page, Copyright information, Table of Contents, the Conference Committee listing and the Introduction.

Gamma-ray astronomy in the MeV range suffers from weak fluxes from sources and high background in the nuclear energy range. The background comes primarily from neutron-induced gamma rays with the neutrons being produced by cosmic-ray interactions in the Earth's atmosphere, the spacecraft and the instrument. Compton telescope designs often suppress this background by requiring coincidences in multiple detectors and a narrow time-of-flight (ToF) acceptance window. The COMPTEL experience on the Compton Gamma Ray Observatory shows that a 1.5-ns ToF window is insufficiently narrow to achieve the required low background count rate. Furthermore, neutron interactions in the detectors themselves generate an irreducible background. Judicious choices of instrument materials and new spacecraft designs improve the situation. However, large gains come from new scintillator technology that combines intrinsic neutron insensitivity with exceptional speed to reduce the instrument background rate by upwards of 90%, thereby greatly improving the sensitivity of searches and measurements, while simultaneously improving energy and angle resolution.

Modern Radiography technology was combined with radiation physics and modern imaging processing, which was an important branch of information obtainment and processing. We can get the inside information of the object, by the X ray's attenuation when the ray penetrated the object, and depending on the computer's fast processing, we can see the slice imaging of the object. Computerized Tomography, Computerized Laminography, and Digital Radiography were important parts in Radiography. The institute of applied electronics, CAEP in the research of intense radiation had developed several advanced radiation sources and some advanced radiography imaging systems, for example, S-band small spot linear accelerator, full solid state modulator, C-band linear accelerator, high energy Tera-hertz radiation source and CT technology based on cone beam, DR technology, CL Technology etc. Such imaging systems had been applied in industrial NDT/NDE, security check, medical diagnosis, petroleum and gas pipeline inspection system etc.

We have examined application feasibility of THz time-domain spectroscopy (THz-TDS) to inspect 30 kinds of illicit drugs, 20 kinds of amino acid and 10 kinds of explosives and related compounds (ERCs). We also have got their fingerprints, established the corresponding database, and propose the reference-free methods to extract the absorption or reflection spectra, respectively. We also use optical pump THz probe to research the ultrafast dynamics of semiconductor. While, we also present some new THz imaging techniques, such as, focal-plane multiwavelength phase imaging, reference-free phase imaging, polarization imaging, and continuous-wave (CW) standoff distance imaging.

The optical absorption properties of semiconductors and their nanostructures under intense terahertz (THz) radiation are investigated theoretically. We derived the extended Semiconductor Bloch Equations (SBEs), which include the effects of the Coulomb interaction among the photoexcited carriers and the effects of the applied external classical (static and/or THz) electric and magnetic fields. We presented two formulations of the SBEs in wavevector space and real space, respectively, which are appropriate to analyzing respective semiconductor structures. Different semiconductor nanostructures (such as quantum wells, quantum wires, quantum rings, quantumdot- superlattice nanowires, and quantum-dot-superlattice nanorings) in different configurations of the applied external fields (with the THz electric field applied along the heterostructure interface or the growth-direction) are considered. We showed that the driving of the THz field can give rise to many intriguing phenomena, such as THz dynamical Franz-Keldysh effect, ac Stark effect, THz-sideband, replica of dark exciton states. We also suggested some potential application of these new phenomena in developing novel semiconductor optoelectronic devices.

Terahertz time-domain spectroscopy (THz TDS) holds high potential as a non-destructive, non-contact testing tool. We have identified a plethora of emerging industrial applications such as quality control of industrial processes and products in the plastics industry. Polymers are transparent to THz waves while additives show a significantly higher permittivity. This dielectric contrast allows for detecting the additive concentration and the degree of dispersion. We present a first inline configuration of a THz TDS spectrometer for monitoring polymeric compounding processes. To evaluate plastic components, non-destructive testing is strongly recommended. For instance, THz imaging is capable of inspecting plastic weld joints or revealing the orientation of fiber reinforcements. Water strongly absorbs THz radiation. However, this sensitivity to water can be employed in order to investigate the moisture absorption in plastics and the water content in plants. Furthermore, applications in food technology are discussed. Moreover, security scanning applications are addressed in terms of identifying liquid explosives. We present the vision and first components of a handheld security scanner. In addition, a new approach for parameter extraction of THz TDS data is presented. All in all, we give an overview how industry can benefit from THz TDS completing the tool box of non-destructive evaluation.

Characterization of doped ZnCdTe crystals as terahertz (THz) emitters is studied in detail. By measuring the absorption of THz wave and analyzing the phase matching condition in these crystals, it is found that the dispersion property of crystals and the self-absorption of THz waves in these crystals play important roles in THz radiation. It is also found that the direct current (DC) resistivity of the crystal for THz emitter application should be greater than 10⁶Ωcm. The THz generation efficiency increases as their DC resistivity increases, but the efficiency saturates and even declines when the resistivity goes beyond 10⁶Ωcm.

In material recognition, distilling eigenvalue will use an object's true gray levels. The problem is objects in a bag almost always overlap with others. Being able to identify the object of interest and remove the overlap effects becomes the key issue that needs to be solved. First, the author took an n-object-overlapping problem simplified to a two-object-overlapping problem. So the research focus turned to computing true gray levels for two-object-overlapping problem. It was necessary to develop models that can be used to remove the background object overlapping effects. The author took transmission images for example, discussed the development of the mathematical model for removing the overlapping effects, solved the model parameter by experiment and analyzed model error. The mathematical models for forward-scatter and backscatter overlap models were much more complicated than transmission overlap models. However, these formulas could still be derived in a similar manner as was employed to create transmission models. This method has been used in DEX9080B x-ray security inspection equipment of DT Inspection equipment limited company. The results of application show that the algorithm is feasible. This is a unique contribution to the explosive detection community.

Starting from exploiting the applied detection system of gas transmission pipeline, a set of X-ray image processing methods and pipeline flaw quantificational evaluation methods are proposed. Defective and non-defective strings and rows in gray image were extracted and oscillogram was obtained. We can distinguish defects in contrast with two gray images division. According to the gray value of defects with different thicknesses, the gray level depth curve is founded. Through exponential and polynomial fitting way to obtain the attenuation mathematical model which the beam penetrates pipeline, thus attain flaw deep dimension. This paper tests on the PPR pipe in the production of simulated holes flaw and cracks flaw, 135KV used the X-ray source on the testing. Test results show that X-ray image processing method, which meet the needs of high efficient flaw detection and provide quality safeguard for thick oil recovery, can be used successfully in detecting corrosion of insulated pipe.

Ultrafast carrier dynamics in semiconductors has attracted much attention due to the application in high speed devices. Compared to the conventional experimental techniques, such as the time-resolved optical transmission technique and the all-optical pump-probe spectroscopy, the optical pump-terahertz probe spectroscopy has a plethora of advantages to provide the ability to temporally resolve phenomena at the fundamental timescales of carrier motion. The distinct advantage of OPTP is being able to directly measure the photo-induced changes in the photoconductivity, which contains the information of carrier density and mobility, with a temporal resolution of sub-picosecond. The ultrafast carrier dynamics and transient terahertz photoconductivity in semi-insulating GaAs have been investigated under electric field by using optical pump-terahertz probe technique with an unchanged pump power irradiating on the GaAs surface. One-dimensional pump scan at the maximum value of the THz pulse under electric fields of 0 kV/cm, 6 kV/cm, and 15 kV/cm, respectively. The measurements indicate that the terahertz transmission change induced by the pump pulses at high electric field is smaller than that without electric field. It is obvious that the threshold value of E, which begins to enhance the transmission, is about 3 - 4 kV/cm. We attribute this phenomenon to carrier scattering into the L valley or even X valley, which leads to a drop in carrier mobilities due to the large effective masses in those satellite valleys. The calculated transient photoconductivities fit well with the Drude-Smith model, which attributes the negative imaginary conductivity to the backward scattering of electrons. The negative value of c1 in our fitting implies that a fraction, but not all, of the backward scattering is a result of the electron reflecting from surfaces. It could also result from a Coulombic scattering between carriers. Due to the low mobilities of electrons in the L valley, the average mobility of all electrons will decrease under high E. These fitting results are consistent with our intervalley scattering model. Our investigation suggests that the OPTP technique is a very promising method for detecting the ultrafast dynamics in those materials.

Femtosecond pump-terahertz probe studies of carrier dynamics in semi-insulating GaAs have been investigated in detail for various pump powers and at electric fields up to 15 kV/cm. The pump-induced attenuation of THz transmission reduces obviously at high field, and the carrier relaxation time is also found to be correlated with photo-injected carrier density and electric field. These effects can be fully explained in terms of the carrier intervalley scattering and the surface states filling in GaAs, which may influence the carrier recombination process. Moreover, the carrier screening effect at high pump powers is also discussed.

A space spectrograph main structure is optimized and examined in order to satisfy the space operational needs. The space spectrograph will be transported into its operational orbit by the launch vehicle and it will undergo dynamic environment in the spacecraft injection period. The unexpected shocks may cause declination of observation accuracy and even equipment damages. The main frame is one of the most important parts because its mechanical performance has great influence on the operational life of the spectrograph, accuracy of observation, etc. For the reason of cost reduction and stability confirming, lower weight and higher structure stiffness of the frame are simultaneously required. Structure optimization was conducted considering the initial design modal analysis results. The base modal frequency raised 10.34% while the whole weight lowered 8.63% compared to the initial design. The purpose of this study is to analyze the new design of main frame mechanical properties and verify whether it can satisfy strict optical demands under the dynamic impact during spacecraft injection. For realizing and forecasting the frequency response characteristics of the main structure in mechanical environment experiment, dynamic analysis of the structure should be performed simulating impulse loads from the bottom base. Therefore, frequency response analysis (FRA) of the frame was then performed using the FEA software MSC.PATRAN/NASTRAN. Results of shock response spectrum (SRS) responses from the base excitations were given. Stress and acceleration dynamic responses of essential positions in the spacecraft injection course were also calculated and spectrometer structure design was examined considering stiffness / strength demands. In this simulation, maximum stresses of Cesic material in two acceleration application cases are 45.1 and 74.1 MPa, respectively. They are all less than yield strengths. As is demonstrated from the simulation, strength reservation of the frame is adequate, but amplitudes of some key positions' dynamic responses are numerically too high. It need be emphasized in the next stage of design and experimental research.

The study of the sheet-beam extended interaction oscillator, a compact, low voltage (~12kV) high power terahertz radition source is presented in this paper. In this structure, the sheet beam interacts with the electromagnetic mode of TM₃₁, 2π mode, and the generated electromagnetic wave is coupled and enhanced in the rectangle cavities. The sheet beam, high mode operation and rectangular cavity are helpful to enhance the beam-wave interaction, increase the frequency and the coupling strength, respectively. A 0.1THz cavity is designed, with cathode voltage of 12KV, beam current of 0.6A, and the guiding magnetic field strength of o.5T, simulation results show that the electromagnetic wave is generated with the frequency of 0.1THz and the peak power of 1kW at the output window.

The focus of this paper is to investigate an accurate deflection angle distribution on the key portion for the bent focusing mirror subassembly in nonlinear analysis. Bent focusing mirror system is the heart of the Shanghai Light Source beam-line, which can realize beam deflecting, collimating and focusing .Big errors were existed in the past of using linear method analyzing nonlinear parts for bent focusing mirror subassembly. In test of the system, there is a phenomenon of the rod that is prized, and the linear analysis results don't conform to the test result. It is concluded that there is friction between rod and sleeve, which result in the phenomenon of prized rod. To solve the problem, the contact and nonlinear analysis method are introduced in this paper. After summarized the main factors for structural nonlinearity, a concrete contact nonlinear analysis of bent focusing mirror subassembly is given. A comparison in the bent focusing mirror subassembly by nonlinear and linear analysis is carried out. The results indicate that contact nonlinear analysis is more accurate than linear analysis and closer to real system in engineering analysis of bent focusing mirror subassembly. The mirror distortion result under given temperature load is also given.

In the latest 20 years, for the needed of the inertial confinement fusion(ICF) created by laser, the grazing incident microscopes are more interested., KBA x-ray microscope is preferred among the ICF diagnostic experiment devices. In order to study the ICF experiment (energy range abour the energy 0-3keV), we design and manufacture a set of KBA microscope. The resolution of 5μm can be obtained in the 2 mm field of view. According to the effective blur diameters, we establish the tolerances. We also analyze the reflectivity of two manufacturing methods. Taking the non-coaxial grazing incident KBA microscope designed as an example, x-ray reflecting from metal surface and single film layer are discussed. At a wavelength of 0.83 nm, the influence of the surface root-mean-square roughness (RMS) on reflectivity is analyzed, and x- ray reflectivity of this system is calculated. The results illustrate that reflectivity decreases with RMS increasing. Reflectivity of Cu is 0.021 and that of single film layer is 0.049, thus KBA X-ray microscope is made of single film layer. It met the requirement of the needed.

This paper addresses impact of frequency source noise in terahertz (THz) moving objection detection systems. Oscillator noise deserves special attention in terahertz (THz) moving objection detection systems since phase jitter in high-power THz frequency source is relatively serious. Such phase jitter (noise) will lead to a few serious problems and seriously affect performance of THz moving object detection systems. In this paper, quantitative estimates of impact of frequency source noise in THz moving target detection systems are derived analytically and requirement for coherent accumulated time limited by frequency source phase noise is deduced based on the second-order statistics characteristic of the oscillator phase noise. This research results could further consummate THz theory system and provide theory basis for the system design.

With advances in millimeter-wave technology, passive millimeter-wave (PMMW) imaging technology has received considerable concerns, and it has established itself in a wide range of military and civil practical applications, such as in the areas of remote sensing, blind landing, precision guidance and security inspection. Both the high transparency of clothing at millimeter wavelengths and the spatial resolution required to generate adequate images combine to make imaging at millimeter wavelengths a natural approach of screening people for concealed contraband detection. And at the same time, the passive operation mode does not present a safety hazard to the person who is under inspection. Based on the description to the design and engineering implementation of a W-band two-dimensional (2D) planar scanning imaging system, a series of scanning methods utilized in PMMW imaging are generally compared and analyzed, followed by a discussion on the operational principle of the mode of 2D planar scanning particularly. Furthermore, it is found that the traditional radiometer uncertainty equation, which is derived from a moving platform, does not hold under this 2D planar scanning mode due to the fact that there is no absolute connection between the scanning rates in horizontal direction and vertical direction. Consequently, an improved radiometer uncertainty equation is carried out in this paper, by means of taking the total time spent on scanning and imaging into consideration, with the purpose of solving the problem mentioned above. In addition, the related factors which affect the quality of radiometric images are further investigated under the improved radiometer uncertainty equation, and ultimately some original results are presented and analyzed to demonstrate the significance and validity of this new methodology.

A new method for quantitative analysis of mixtures of illicit drugs with THz time domain spectroscopy was proposed and verified experimentally. In traditional method we need fingerprints of all the pure chemical components. In practical as only the objective components in a mixture and their absorption features are known, it is necessary and important to present a more practical technique for the detection and identification. Our new method of quantitatively inspect of the mixtures of illicit drugs is developed by using derivative spectrum. In this method, the ratio of objective components in a mixture can be obtained on the assumption that all objective components in the mixture and their absorption features are known but the unknown components are not needed. Then methamphetamine and flour, a illicit drug and a common adulterant, were selected for our experiment. The experimental result verified the effectiveness of the method, which suggested that it could be an effective method for quantitative identification of illicit drugs. This THz spectroscopy technique is great significant in the real-world applications of illicit drugs quantitative analysis. It could be an effective method in the field of security and pharmaceuticals inspection.

A two dimensional raster scanning terahertz imaging system based on a continuous backward-wave oscillator (BWO) terahertz source is built up. To improve the spatial resolution of the system, a scanning step smaller than the focused spot size of the terahertz beam is used to get the transmission image. After pre-processing of the image with wavelet filtering, and using incremental Wiener filtering for image restoration, a terahertz image with resolution higher than the diffraction limit of the system can be obtained. Our imaging experiment shows that this method can both enhance spatial resolution and suppress imaging noise effectively.

A highly birefringent elliptical-hole terahertz fiber with squeezed lattices is proposed. The THz fiber is formed through regular linear deformation of a circular porous fiber by squeezing it in one direction, which can be fabricated easily with the sophisticated fabrication technology. A finite element method is used for the simulation and numerical analysis of the guiding and birefringent properties of the fiber structure. It will be shown that with a moderate extent of deformation the proposed THz fiber can exhibit high birefringence on a level of 10^-2 in a wide THz frequency range. And material absorption caused guiding loss of the THz fiber can be reduced effectively, since a dominant fraction of modal power distributes in the air holes inside dielectric material.

In Terahertz continuous-wave laser scanning imaging system, the laser output power's fluctuation and the aperture effects of a finite focus diameter have significant influence on the image quality, which reduces the image resolution and causes the imaging noise. The most common problem of image denoising is that some interesting structures in the image will be removed from the concerned image during noise suppression. Because Markov random field (MRF) can be used to describe the spatial continuity, the structures of images can be modeled if a proper neighborhood system is selected. Therefore, MRF and simulated annealing are used to suppress the image noise and increase the image resolution. Simulation and experiment show that the method can preserve the object structures of THz images.

The absorption spectra of rice bran oil in the frequency range of 0.2~1.6THz has been measured with terahertz timedomain spectroscopy (THz-TDS) at room temperature in nitrogen atmosphere. It is found that hexadecanoidc acid and octadecanoic acid contained in rice bran oil has the spectral response to terahertz waves in this frequency region. Simultaneously, the corresponding theoretical spectra were given by using DFT methods with the aid of Gaussian03. The experimental spectra are well comparable with the calculated spectra and these results mutually validated both approaches. It was found that the absorption peaks of the two molecules obtained by theoretical were in good agreement with the experimental results. The research results prove the feasibility of applying THz-TDS technique to detect and identify of main component of edible oil. Furthermore, the result s provided in this paper will help us to study the THz application to food quality evaluation or safety inspection further.

The spectral characteristics of corn oil after five minutes and ten minutes of boiling in the rang from 0.2THz to 1.5THz have been measured with THz time-domain spectroscopy (THz-TDS) at room temperature in nitrogen atmosphere. A novel iterative algorithm is employed to determinate the optical properties considering the effect of the cuvette. The refractive indices of the two corn oil samples show slow a decrease as the terahertz wave frequency increases. The power absorption coefficients increase as the frequency increases within the investigated terahertz wave frequency range. The results provided in this paper will help us to study the THz application to seed oil quality and safety detection further.

In order to observe the spectroscopic characteristics of metallic ion in soil in terahertz region, terahertz time-domain spectroscopy (THz-TDS) was used to analyze the absorption coefficient and refractive index in the frequency range 0.2 ~1.6 THz at room temperature. In the present work, we designed several kinds of soil samples (i.e. different content copper sulphate and zinc sulphate in soil).The terahertz time-domain spectra of samples were measured. The experimental results indicate that the metallic ion in soil has many distinct characteristic spectra between 0.2 and 1.6THz. This study can not only assign the characteristic absorption of the sample, but also can provide the absorption frequencies in wider effective spectra range. The results show that the THz-TDS can be used to measure the metal residues in the soil.

THz transmission imaging is considered as a promising detection measure and imaging method with wide application prospect in security inspection and counter-terrorism. And high-speed array imaging is a very important direction. In this paper, 2.45-THz transmission imaging experiments are made by applying a 124×124 array detector. The 2.45-THz CW CO2-pumped laser is used as illumination source and its output power is about 17mW. Some undersize articles (gasket, screw and nut) are chosen as objects. THz imaging experiments are respectively demonstrated through 1-2 pieces of paper and two kinds of envelopes to show the imaging effect. The original data is acquired and some image processing methods (5-frame average, median filtering, etc) are used to improve the image effect. Finally the THz images obtained are basically clear. The experimental results show that utilizing the setup designed for 2.45-THz imaging, the images are fast generated and objects' contours are clear through paper and envelop.

A simple wet-chemical route has been employed to synthesize β-ZnS nanoparticles with diameter of ca.15-20 nm. The far-infrared characteristics of β-ZnS nanoparticles are investigated by terahertz time-domain spectroscopy (THz-TDS) over the frequency range from 0.3 to 2.5 THz. The observed results show two obvious absorption features at 1.44 and 1.72 THz, which give rise to different vibration modes compared to the bulk ZnS. The theoretical calculation has been carried out for better understanding the vibration behaviors by using of density functional theory (DFT) with GAUSSIAN 03 software package. The simulated absorption spectrum was consistent with the experimental data. The results reveal that the two absorption features are mainly ascribed to different vibration modes caused by the surface atoms.

In the paper, the two-dimensional THz imaging methods are described. The SIFIR-50 FPL Far-Infrared Laser is used as the THz source. The output frequency is 2.5THz in the experiment, because the THz laser operates steadily at this frequency. The P4-42 detector works at room temperature and offers relatively high sensitivity. The software of THz imaging system is self-designed, and it plays a crucial role in this imaging system because it controls nearly all the operations of this system, including the two-dimensional scanning, image data collection, image data storage, image display and image processing. Utilizing this setup, THz transmission images of concealed objects are obtained. In the experiment, a bottle cap and a plastic board covered by reflective materials are chosen as the imaging objects; paper and Teflon are placed before the object to test the transmission imaging effect. The experimental results show that this imaging system can generate clear images.

With the rapid growth of the application of Terahertz time-domain spectroscopy (THz-TDS) in many scientific fields, the accurate temporally-resolved THz electric field oscillation is required. However, distortion occurs in electro-optic sampling (EOS) measurements of THz pulse field. In this paper, a time-domain analysis of the distortion in the electro-optic sampling measurement of THz pulses is made with the convolution theory, in which frequency-dependent reflection and electro-optic (EO) effect, dispersive propagation of the THz pulse in the EO crystal, and the phase mismatching between the THz pulse and the sampling lase pulse in the EO crystal are taken into account. And then, a retrieval algorithm for high accurate THz pulse field reconstruction is proposed and numerically demonstrated. Since the reconstruction of the THz pulse field is an ill-posed inverse problem caused by noise, the iterative Tikhonov regularization is adopted in our retrieval algorithm to convert this ill-posed problem to a related well-posed problem. Gallium phosphide (GaP) is used as the EO crystal to reduce the sensitivity of this ill-posed problem, for the complex-dielectric function of GaP is flat within a broader THz range than that of commonly used ZnTe crystal. Phase mismatching arises when GaP crystal is utilized, our proposed retrieval algorithm is demonstrated to have a good performance even when a 0.5-mm-thick GaP crystal (with severe phase mismatching) is used.

Infrared (IR) transmission spectra and IR microscopy images were measured to evaluate the sliced CdZnTe crystals grown under different starting charges using modified vertical Bridgman method. Upon comparing the corresponding electric properties and charge transport performance, IR absorption within the wave-number range from 500 to 2500 cm^-1 was potentially attributed to the free carrier absorption caused by the ionized impurities. The size and density of Te particles were not sensitive to IR transmission spectra over the same wave-number range. However, the electric field was modified around isolated Te particles, in such a way that the impurities gettering in the Te inclusions. With respect to the high resistive CdZnTe crystals, IR transmission measurements demonstrated that the mean transmittance is higher than 60% in the wave-number region from 500 to 4000 cm^-1. IR microscopy shown the typical diameters of Te particles present in the material were in the range of 6-9 μm, and the density of the particles was 1-4×10⁵ cm^-3. The obtained electron mobility lifetime product (μτ)e value was in the range of 1-3×10^-3 cm²·V^-1 by using well-known alpha particle spectra at room temperature. The fabricated CdZnTe thin planar detector showed the typical energy resolution was approximately 5.7% for the 59.5 keV peak at room temperature, without any additional signal processing.

CdZnTe (CZT) is one of the most promising materials for room-temperature X-ray and Gamma-ray detectors. The electrical properties of CZT crystal decide the performance of CZT detector to a large degree. For high quality CZT crystal using as detector, both high resistivity and high carrier transport properties are necessary. In this paper, the electrical properties and defect levels of Al-doped CZT (CZT:Al) crystal were discussed. Utilizing the thermally stimulated current (TSC) spectroscope measurement, the defect levels in CZT:Al crystal and their level-model were determined and inferred. The carrier transport properties of the CZT:Al were charactered with the carrier mobility-lifetime (μτ) products determined by the peak channel of²⁴¹Am alpha particle 5.48 MeV spectrum as a function of the bias voltage. Fitted by the single carrier Hecht equation, the μτ for the electron was evaluated to be 4.6×10^-4 cm²·V^-1.

We present a terahertz two dimensional phase imaging method with multiwavelength. This novel approach can image object with larger optical length compared to using the largest wavelength in the terahertz spectrum and does not involve the usual phase unwrapping in the detection of phase discontinuity. Furthermore, this technique can significantly decreases the background noise and allows one to resolve very fine structures for non-destructive detection. The validity of this new method can be demonstrated by processing the terahertz raster-scan two-dimensional(2D) image data of a polyethylene wedge and a piece of foam with a rectangle groove. The measurements show that the multiwavelength phase imaging is a straightforward and efficient phase data processing method in terahertz imaging application.

The powerful conveyer belt is widely used in the mine, dock, and so on. After used for a long time, internal steel rope of the conveyor belt may fracture, rust, joints moving, and so on .This would bring potential safety problems. A kind of detection system based on x-ray is designed in this paper. Linear array detector (LDA) is used. LDA cost is low, response fast; technology mature .Output charge of LDA is transformed into differential voltage signal by amplifier. This kind of signal have great ability of anti-noise, is suitable for long-distance transmission. The processor is FPGA. A IP core control 4-channel A/D convertor, achieve parallel output data collection. Soft-core processor MicroBlaze which process tcp/ip protocol is embedded in FPGA. Sampling data are transferred to a computer via Ethernet. In order to improve the image quality, algorithm of getting rid of noise from the measurement result and taking gain normalization for pixel value is studied and designed. Experiments show that this system work well, can real-time online detect conveyor belt of width of 2.0m and speed of 5 m/s, does not affect the production. Image is clear, visual and can easily judge the situation of conveyor belt.

As interplanetary missions are increasingly complex, the existing unique mature interplanetary navigation method mainly based on radiometric tracking techniques of Deep Space Network can not meet the rising demands of autonomous real-time navigation. This paper studied the applications for interplanetary flights of a new navigation technology under rapid development-the X-ray pulsar-based navigation for spacecraft (XPNAV), and valued its performance with a computer simulation. The XPNAV is an excellent autonomous real-time navigation method, and can provide comprehensive navigation information, including position, velocity, attitude, attitude rate and time. In the paper the fundamental principles and time transformation of the XPNAV were analyzed, and then the Delta-correction XPNAV blending the vehicles' trajectory dynamics with the pulse time-of-arrival differences at nominal and estimated spacecraft locations within an Unscented Kalman Filter (UKF) was discussed with a background mission of Mars Pathfinder during the heliocentric transferring orbit. The XPNAV has an intractable problem of integer pulse phase cycle ambiguities similar to the GPS carrier phase navigation. This article innovatively proposed the non-ambiguity assumption approach based on an analysis of the search space array method to resolve pulse phase cycle ambiguities between the nominal position and estimated position of the spacecraft. The simulation results show that the search space array method are computationally intensive and require long processing time when the position errors are large, and the non-ambiguity assumption method can solve ambiguity problem quickly and reliably. It is deemed that autonomous real-time integrated navigation system of the XPNAV blending with DSN, celestial navigation, inertial navigation and so on will be the development direction of interplanetary flight navigation system in the future.

A high beam quality foilless diode for high power 0.14 Terahertz backward wave oscillator (BWO) is presented in this paper. Limited by the wavelength in terahertz region, the diode is so small that its cathode radius is only 2.5 mm, and its anode radius is 9 mm. Based on an empirical formula for foilless diode, the initial structural parameters are estimated. Then the static electric field simulations with Superfish code and particle simulations using a 2.5 dimensional UNIPIC code are performed to optimize these parameters. The simulation results show that the beam parameters satisfy our design requirements. Finally, the experiments of the diode are carried out. The copper targets by beam bombardment are measured to prove that the electron beam is azimuthally uniform with an inner radius of 2.0 mm and outer radius of 2.54 mm. From the experimental results, the diode can provide a high quality beam over a wide range of diode voltage (160 kV<U<220 kV) and current (600 A<I<1.5 kA). Meanwhile, the diode resistance versus the distance between the cathode and anode is compared with numerical simulations. This foilless diode is being used in the experiment of high power terahertz wave generation.

Extraordinary transmission spectrum of a copper film pierced with a periodic array of subwavelength rectangular holes is measured by the terahertz time-domain spectroscopy. The transmission coefficient is strongly depended on the angle between the polarization of terahertz electric field and the latitudinal direction of the periodic apertures. When the angle increases from 0° to 90°, a transmission peak becomes stronger and another peak reduces. The transmission is proposed to be the contributions of the localized surface plasmons inside the apertures. The finite-difference-time-domain (FDTD) simulation results are in good agreements with the experimental observations.

Microwave vacuum electron devices (MVED) are capable of handling more power in a smaller interaction volume than the solid-state devices. An over-mode high power terahertz backward wave oscillator (BWO) is proposed. The slow wave structure (SWS) is constructed as follow: a series of equidistant annular slots are cut in the inner wall of a cylindrical waveguide. The dispersion relationship of the SWS is theoretically analyzed. The parameters of this structure are optimized by using 2.5D UNIPIC code. The influences of structure parameters and working parameters on the performance of the device are investigated, such as the period number of the SWS, the beam voltage, and the strength of external guiding magnetic field. The numerical results indicate that the frequency of the device is not sensitive to the beam voltage. This is the typical characteristic when the device works at π-mode. Under the condition of the electron beam with the voltage of 200 kV, the current of 1100 A, the inner radius of 2 mm , the outer radius of 2.5 mm, and magnetic field of 5 Tesla, the TM01 mode wave begins to oscillate at 3.5 ns, whose average power is about 30 MW, frequency is 0.147 THz. And an efficiency of 14% is also obtained with a fine spectrum characteristic. The numerical results demonstrate that the over-mode electrodynamic structure can be used to decrease internal electric field strength while avoiding multimode generation and maintaining good spectral purity.

Various periodic plasma structures have been obtained by nonlinear self-organization in dielectric barrier discharge with two water electrodes. The spatio-temporal evolvement of these plasma structures has been studied when changing the discharge parameters. Based on the experimental results, a potential tunable plasma photonic crystal for microwave to THz wave control is suggested. In addition, a special superlattice plasma structure is observed, in which three disparate refractive indexes are modulated periodically.

In this work, an Al-N-co-doped p-type ZnO film was deposited on the smooth nucleaction side of freestanding diamond film by radio-frequency (RF) reactive magnetron sputtering method. An intrinsic n-type ZnO layer was deposited on the p-type Al-N-co-doped ZnO film to fabricate ZnO p-n homojunction. The electrical properties of ZnO p-n homojunction in dark condition were investigated by a Keithley 4200/SCS digital semiconductor characterization system. The result exhibited the distinct rectifying current-voltage (I-V) characteristics with a turn-on voltage of ~2.2V. The homojunction was also used for UV photodetector application. Spectral response of the detector showed a significant discrimination between UV and the visible light.

Using the terahertz time-domain spectroscopy (THz-TDS), the frequency-dependent absorption coefficient(s) and refractive index (indices) of selected lube base oil (LBO) were extracted in the spectral range of 0.3-1.6 THz. The selected LBO was also characterized by near-infrared spectrum. The experimental results reveal that LBO is more sensitive in the THz range than near-infrared, and the different viscosity index of LBO can be identified according to their different spectral features in THz range. Due to better repeatability, shorter testing time, and easy operation, THz- TDS can be used as a complementary for identifying the chemical composition of LBO.

As a valuable material for the detecting of γ-ray, PbWO₄ and BaF₂:PbWO₄ crystals were grown by a novel multi-crucible temperature gradient system developed by ourselves. Utilizing a topical partial heating method, this system can form a topical partial high temperature in its hearth. Thus this system could melt raw materials in step by step as requirement. The advantage of this method is that there would be solid obstruct left on the melt in the procedure of the crystal growing up. The left obstruct could prevent the volatilization of the component in the melt. Hence it is helpful for the composition homogenization in the crystal. The system also offers a sustaining device for multi-crucibles and thus it can grow many crystals simultaneity. The optical properties and scintillation properties of the crystals were studied. The results reveal that the ions doping improves the scintillation properties of the crystal. The transmittance spectra show that the transmittance of BaF₂:PbWO₄ crystals are better than that of PbWO₄ crystals. For the PbWO₄ crystals, their absorption edge is at 325nm, and their maximum transmittance is 68%. For the BaF₂:PbWO₄ crystals, their absorption edge is at 325nm and their maximum transmittance is upto76%. The X-ray excited luminescence spectra shows that the luminescence peak is at 420nm for the samples of PbWO₄ crystal while the peak is at 430nm for the samples of BaF₂:PbWO₄ crystal respectively. The luminescence intensity of the samples of BaF₂:PbWO₄ crystal is about two times than that of PbWO4 crystal. And their peak shape is different for the two kind of crystal. The light yield of BaF₂:PbWO₄ crystals is about 2.9 times than that of PbWO₄ crystal Analyzing these scintillation properties, we find that the V_Pb ³⁺ and V_O- defects do harm for the optical properties of the crystal. Ions doping method could reduce the defect concentration and improving its illumination performance of the crystal. Specially, the doped F^- ions in O^2- site can induce the aberrance of the [WO4]^2- tetrahedron and form [WO₃F]^- tetrahedron which has more active blue light yield, thus improve the light yield of the crystal. The improved light yield of BaF₂:PbWO₄ crystals is valuable for the medical diagnosing instrument PET and CT with high resolving power

Based on binary optical ideas, the beam shapers are designed for producing pseudo-Bessel beams at THz. In order to analyze precisely the properties of pseudo-Bessel beams generated by the designed shapers, a rigorous electromagnetic calculation method is employed. This is to associate a two-dimensional finite-difference time-domain (2-D FDTD) method, for determining the fields diffracted by the beam shapers in the near region, with Stratton-Chu formula (SCF), for compute the fields in the far region. The numerical results and conclusions are given in our paper.

The propagation properties of terahertz (THz) wave propagating along conical metal wire have been investigated. The effects of composed materials, metal wire diameter and temperature on waveguide characteristics have been shown and discussed. The numerical calculation agrees well with the experimental results and predicts that metal wire waveguide shows better propagation properties at lower temperature. The energy concentration at the end-tip increases with the decreasing of frequency, end-tip diameter and temperature. The conical metal wire tip can be used to measure the changes of temperature accurately because the energy density is very sensitive to temperature, showing great potential in the field of THz spectroscopy, imaging and sensing.

In this paper, the propagation characteristics of THz wave through two-dimension photonic crystals of square lattices are studied. The band structures of photonic crystals are calculated by means of the plane wave expansion (PWE) and the self-compiled MATLAB program. It is found that when lattice constant is the scale of sub-millimeter, the periodic dielectric with air cylinders in silicon (ε =11.9 ), gallium arsenide (ε =13.6 ), and germanium (ε =16.0 ) matrix can generate the absolute photonic band-gaps (PBG) at terahertz frequencies. The larger photonic band-gap can be obtained by increasing the difference of dielectric constant properly. The relation between the maximum PBG and the filling ratio for germanium with the larger PBG is given. These results provide theoretical guide for the development of THz waveguide devices.

Recently, system designers have looked toward the higher frequency, shorter wavelength (to THz), consequently the device requires smaller and more precision. And this paper describes a polarization converter works in the radar system set-up at 225 GHz. Its working principle is similar to the optical diffraction. After simulations, the model size is confirmed and the data show a good result. And this component have an advantage is easy to machining. It also can be used in other frequency band through adjusting its size.

For the X-ray real time imaging system base on image intensifier, the non-uniformity response among each pixel channel can not be ignored, which cause the fixed pattern noise and degrade the image quality obviously. In order to correct the non-uniformity response, a logarithm response model is created to fit the output-input characteristic curve of each pixel channel, then the correction coefficient table is obtained to make each pixel channel has the same response sensitivity. In practical application, the un-corrected image is divided by the correction coefficient table to get rid of the fixed pattern noise. The experimental results prove that the algorithm has an efficiency of real time correction and the corrected image quality can be increased effectively.

Many terahertz systems have been put forward and some of them even find space application. Continuous-wave (CW) terahertz sources will play an important role in space systems. Many CW terahertz techniques have been realized in laboratory and even employed. Those proper must be pre elected for space systems with strict limitation. Some space terahertz applications are introduced and CW terahertz sources compared. Among them prospective source technology for space are stressed.

In this paper, we present the calculation of the impedance and beam pattern of a 6×6 twin-slot antenna array combined with an extended hemispherical silicon lens. The self and mutual impedance of the twin-slot antenna array are simulated by High Frequency Structure Simulator (HFSS), while its radiation pattern is computed by using ray-tracing inside the lens and electric and magnetic field integration on its surface. The distance between two neighboring antennas is set as 282μm (0.61λ₀ at 650GHz) to avoid the overlap between the main-lobe beams of the antenna elements. With good imaging quality (i.e., with a Strehl ratio no less than 0.8), the minimum diameter of the lens is found equal to 23mm (~50λ₀ at 650GHz).

In this paper, we use the Monte-Carlo method to study the reaction of the electron-hole pairs produced to randomicity and the statistics rule, according to the principal of the detector and the gamma ray track in the CdZnTe detector. The EGSnrc software based on Monte-Carlo method is used to simulate the process of carriers' transportation. The statistics rule greatly reflects the result in Monte Carlo simulation. Firstly, we use Ansys software to create a model of the object for Monte-Carlo simulation, which is the basis for our further Monte-Carlo research. During Ansys simulation, a columniform block is created, where the electrical and thermal properties of the materials for simulation use are established. Then, the charge collection efficiency through the statistical approach was calculated using the EGSnrc software. Furthermore, by considering the interaction mechanism of CdZnTe with gamma ray, several modules in the software are added into Monte Carlo simulation. Finally, the pulse height spectra with the response to gamma ray, are available from the simulation. The comparison between the simulation and the measurement result is indicated, which shows that the simulation experiment is reliable. The Frisch grid detector can get the responses more efficiently than other structure devices.

Observations in tera-hertz astronomy can only be done at a site with good atmospheric transmission at millimeter and submillimeter wavelengths. With extremely dry weather and calm atmosphere resulted by high altitude and cold temperature, Dome A (or Dome Argus), Antarctica, is possibly the best site on this earth for THz astronomy. To evaluate the site condition there, we are constructing a Fourier Transform Spectrometer (FTS) based on Martin-Puplett interferometer to measure the atmospheric transmission in the frequency range of 0.75~15THz. The whole FTS system is designed for unattended and outdoor (temperatures even below -70 degrees Celsius) operation. Its total power consumption is estimated to be approximately 200W. This contribution will give a brief overview of this FTS development.

The terahertz spectra of pure melamine and two kinds of its mixtures that mix with polyethylene and milk powder were measured using the terahertz time-domain-spectroscopy (THz-TDS). It was found that there are two absorption peaks at 1.99THz and 2.29THz in all three spectra. The absorption coefficient of the mixture varies with the proportion of melamine in the mixture. Increasing the percentage of melamine in the mixture, the absorption peaks in spectrum get more obvious and sharper. According to the Lambert-Beer law, the absorption coefficient and the proportion of the melamine should followed linear relationship. The experimental data accord to this theory well. Using density functional theory, the vibration of melamine crystal was calculated, which accords to experimental data well. This work provides a method of detecting melamine in milk powders. It is expected that the terahertz spectroscopy technology can be used in food safety and other applications.

A method for measuring the refractive index of metal bulks in the terahertz region with terahertz time domain vertical reflection spectroscopy is proposed. In the experiment, the terahertz wave forms generated by laser induced air plasma and reflected by a silicon wafer and metal bulks are measured respectively. The Kramers-Kronig transformation is used to reduce the phase shift error that influences the accuracy on the experimental results. The refractive index of a silicon wafer, which was measured with terahertz time domain transmission spectroscopy, is used as a reference in the terahertz time domain reflection spectroscopy. Therefore the complex refractive index of metal has been obtained by the Fresnel law in the presence of the known silicon refractive index. By this method, the refractive indices of aluminum and copper plates in the terahertz region are measured, furthermore, these experimentally obtained results are discussed with the simple Drude model.

In this paper, the composition, morphology and electrical properties of the passivation layer for CdZnTe detectors were investigated. A two-step passivation was performed under different conditions, including passivation time, temperature and NH₄F/H₂O₂ concentration. The obtained passivation layers were characterized by XRD, SEM, XRF and I-V methods. The results showed that the best passivation condition was with the NH₄F/H₂O₂ concentration of 10wt%, passivation time of 40min and temperature of 20ºC. Under this condition, the passivation layer was purely oxidized and compact, and the surface leakage current of CZT crystals was most effectively reduced.

Aiming at the artifact corrections for batch scans in Cone-Beam Computed Tomography (CBCT) system, the concept of detection model is proposed. Expressing the prior knowledge of CT system and scanned object properties by the detection model, the rapid artifact corrections are achieved based on the object knowledge, which can save the machine consumption, enhance the detection efficiency and improve the correction effect. Based on the Digital Radiography (DR) imaging conditions remained basically unchanged in the batch scans, the modeling method of detection model is established by getting the relevant information through the detected scanning for one of a batch of parts. Finally, the processing flow of CBCT scans and artifact corrections of a batch of parts based on the detection model is given, and some key problems in the flow are discussed to improve the practical operability of the method. The experimental result shows that the modeling method of detection model is feasible, and the rapid CBCT scans and effective artifact corrections can be realized based on the obtained detection model.

China Spallation Neutron Source (CSNS) was under construction since 2008. A two-dimensional thermal neutron detector with sensitive area of 200mm×200mm was constructed for the Reflect Spectrometer of CSNS. The detector was based on two-dimensional cathode strip readout MWPC, using 5.5atm³He+2.5atmC₃H₈ mixture as working gas, and the thickness of the gas volume was 16mm. A readout electronics system was also developed for the detector, which mainly consists of charge-sensitive preamplifiers, amplifiers, charge measurement modules and a 6U VME64x crate. The design maximum neutron count rate of the detector was 10⁵ events per second and the calculated neutron detection efficiency was about 70% for A2 neutrons. A prototype of the detector had been constructed at first, which own an energy resolution (FWHM) of about 23% for ⁵⁵Fe 5.9keV X-ray, and its spatial resolution (FWHM) along the anode wire direction was about 300μm in X-ray test. The detector was then tested by an Am-Be neutron source. The pulse height spectrum of the neutron signal was studied. The detector can work normally and has a good performance in neutron-gamma ray discrimination.

Terahertz Computed Tomography takes the advantages of not only high resolution in space and density without image overlap but also the capability of being directly used in digital processing and spectral analysis, which determine it to be a good choice in parameter detection for process control. But Diffraction and scattering of THz wave will obfuscate or distort the reconstructed image. In order to find the most effective reconstruction method to build THz CT model. Because of the expensive cost, a fan-shaped THz CT industrial detection system scanning model, which consists of 8 emitters and 32 receivers, is established based on studying infrared CT technology. The model contains control and interface, data collecting and image reconstruction sub-system. It analyzes all the sub-function modules then reconstructs images with algebraic reconstruction algorithm. The experimental result proves it to be an effective, efficient algorithm with high resolution and even better than back-projection method.

We experimentally investigate the terahertz energy confinement in finite-width parallel-plate waveguides. Although there is some apparent energy confinement parallel to the plates due to the narrowing of the width, this does not result in actual energy conservation, when the plate separation is as large as 1 cm. However, these findings indicate that by reducing the plate separation, it may be possible to achieve real energy confinement along with energy conservation in these waveguides.

Terahertz Time Domain Spectroscopy (TDS) provides a new way presenting the 'fingerprint' vibrational or rotational absorption spectra of a lot of molecules. For some molecules, their pure rotational spectra within far infrared wavelength range are much easier to be recognized and discriminated than their vibrational spectra in middle infrared. Especially, vapor molecules have obvious absorption lines in the THz range since it has permanent dipole moment while N₂, O₂ ,CO₂ have none permanent dipole moment. So it is possible to detect the vapor content in atmosphere and study dynamics process with terahertz TDS. We measure the vapor's absorption lines in the range of 0.3-2.0THz at different humidity from 10% to 85% at room temperature. The strengths of the vapor absorption lines within this frequency range have been quantitative measured and the absorption coefficients of these absorption lines at different humidity have been calculated. In addition, the THz absorption spectrum has a frequency resolution of 0.004THz so that the locations of most absorption lines can be defined properly and different absorption lines can be distinguished. Seventeen different lines have been identified consistent with previous work. But it is found that the changes of the lines' intensities with humidity do not obey the same trend. Especially, the absorption coefficients of two lines located at 1.6625THz and 1.6735THz have apparently different behavior when the humidity increases. This phenomenon may be due to the interaction between the vapor molecules. Nevertheless, the ratio of the absorptance of these lines can be used in humidity identification for remote sensing.

Terahertz(THz) wave, which lies between infrared and microwave in electromagnetic spectrum, belongs to far-infrared band. THz-wave covers the frequency range from 0.1THz to 10THz. The physical mechanism of terahertz generation was discussed in this paper. It provided theoretical foundation for designing terahertz-generator of LiNbO₃ crystal and optimizing output property of terahertz through the analysis of internal mechanism. The polariton dispersion characteristic was mainly reflected by its dispersion curve. Density functional theory (DFT) was used to calculate Raman spectrum and dispersion curve for LiNbO₃ in this paper. The polariton dispersion curve of LiNbO₃ indicated that the frequencies between 0THz and 7.5THz (the wave numbers were 0cm^-1 250cm^-1) were generated from LiNbO₃ crystal when the scattering angle were about 0 - 5 degree. This predicted theoretically that terahertz was generated from LiNbO₃. It was very obvious that the Raman vibration modes of crystal model were more than molecular structure. Intermolecular vibrations were depicted by molecular structure and parts of vibration modes were simulated. But whole vibration-rotation of unit cell was depicted by crystal model and all atoms were concerned with vibration. It was more accurate that the prediction about generated THz-wave and the range of THz-wave by crystal model than by molecular structure based on the analysis of polariton dispersion curves because crystal model was close to the experimental sample.

A readout integrated circuit for high energy particle detectors is presented. The circuit designed is composed of a Charge Sensitive Amplifier (CSA), a pulse shaper with four selectable peaking time, and an output stage. The readout circuit has been designed in a 0.35um DPTM CMOS technology and tested with Verigy 93000. The size of readout circuit is 1.7*0.7mm². The power supply voltage is 5V. The average gain is about 20.5mV/fC and the Equivalent Noise Charge (ENC) with detector disconnected is 550-650e for five chips in the typical mode. The power dissipation is about 8mW and 2mW respectively, with and without output buffer. The linearity reaches 99.2% in the typical mode. The gain is tunable from 13mV/fC to 130mV/fC and the peaking time varies from 700ns to 1.6us.

A novel coplanar waveguide (CPW)-based composite right/left-handed (CRLH) structure for terahertz (THz) leaky wave antennas (LWAs) application with high directivity and beam steering capability is introduced. The structure of the CRLH-TL was composed of a slot and embedded resonators termed metamaterial resonators using planar CPW technology. There were three steps involved to design the structure of metamaterial resonator and position distribution of metamaterial resonators in the composite right/left-handed (CRLH) transmission lines. First, equivalent circuit model method (also called "transmission line model method") was used to create an equivalent circuit model of the element of metamaterial resonator. Second, from the equivalent circuit model, it was possible to correspond to two basic equivalent circuit parameters "series impedance and shunt admittance" from artificial transmission line structure "CPW-based metamaterial resonator". Finally, the dimensions of metamaterial resonator were calculated and optimized according to the dispersion diagram. Meanwhile, ohmic loss needs to be considered because it is high at THz wave and above frequency region. The LWAs with CPW-based CRLH could implement high-directivity and backward-to-forward beam steering which differs from the conventional one. A balanced CPW CRLH LWA is designed at the transition frequency of 1485 GHz and performances of high-directivity and wide-angle continuous beam-steering are demonstrated.

Many factors influence the radiation power of terahertz (THz) emitters including photoconductive substrate material, antenna geometrical structure and excite light power. In this paper we mainly focus on the performance of semi-insulating (SI) GaAs photoconductive antennas with different geometrical sizes. Three kinds of antennas were prepared with the same structure, material and electrode width (100μm), but with different electrodes gaps of 50μm, 100μm and 150μm, respectively. They were excited by a femto-second fiber laser and tested with THz generation capability. It turns out that the three antennas have a same spectrum scope of 0.2-3THz. The small gap antenna can emit higher THz radiation with lower voltage but it was easy to burn down, that's why a large gap is needed to get higher THz power. Triggered by the same laser of several nJ, peak frequency moves to high frequency with decrease of electrode gaps. Radiation field screening is the dominant causation.

In this paper, the design and fabrication of a capacitive Frisch grid structure for CdZnTe (CZT) detector were investigated. The aging tests were first used to investigate the degradation of the mechanical and electrical characteristics of the CdZnTe detector based on the capacitive frisch grid structure. The effects of the degradation on the performance of CdZnTe detectors were investigated by scanning acoustic microscopy (SAM) test, current-voltage test, and multichannel pulse-height spectrum analysis. In particular, a passivation layer obtained by a two-step passivation processing, combined with a Teflon tape, was used as an insulated layer of the capacitive Frisch grid detector, improving its stability effectively at high voltages. However, further improvements in material and device fabrication (including insulated layer) were required to realize the potential of CZT detectors with the capacitive Frisch grid structure.

The semi-insulating (SI) GaAs photoconductive switch is considered to be the higher efficient THz source recently. In order to make good use of the photoconductive switch to generate the more efficient THz wave, SI-GaAs photoconductive switch's working mechanism is discussed from the respect of EL2 deep level in this paper. It has three operation modes. The SI-GaAs material has many kinds of intrinsic-defects. One of the more notable defects is EL2 deep level. The EL2 level can become an impactful electron trap in the linear operation mode; The EL2 level is also the necessary condition of nonlinear (also known as Lock-on) operation mode emerging in III-V semiconductors such as GaAs and InP. At the same time, the compound operation mode is substantial related with the conversion from neutral energy level EL20 to metastable energy level EL2* and singly ionized energy level EL2⁺ in semiconductor under the light. So in this paper the effects of EL2 deep level are analyzed in photoconductive switch' there operation modes.

The polycrystalline mercuric iodide thick-film array was deposited by hot wall physical vapor deposition (HWPVD) method using an aluminum alloy mask. The pixel size of the 4×4 array is 5×5 mm², and pixel spacing is about 0.2mm. Comparative study of the quality of the films grown on different pixels (type A, B, C) was conducted by Atomic force microscopy (AFM), Scanning electron microscopy (SEM), X-ray diffraction (XRD), and Raman spectroscopy. The results showed that films of all types were all compactly formed by separated columnar monocrystallines with uniform orientation along c-direction and had similar crystalline structures, indicating that the thick films deposited on the substrate had a good uniformity as a whole, and of all the three different type samples, type A were of the relatively highest quality.

The Mercuric Iodide (HgI₂) semiconductor array detectors possess the characters of low noise, high detection efficiency, high energy resolution and working in room temperature. In this work, modified hot-wall physical vapor deposition (HW-PVD) method was used to grow high-quality polycrystalline HgI₂ thin-films on ITO glasses, and then 4×4 and 8×8 HgI₂ array detectors for X-ray radiation were fabricated. We used two fabrication processes for polycrystalline HgI2 array detectors. One was using mask made of stainless steel with good flexibility; while the other was to photo lithography the array on the ITO glass. The main purpose for this work was to compare the electrical properties of polycrystalline HgI₂ array detectors fabricated from different processes, and to find out the optimal process for HgI₂ detectors. Results indicated that the photo lithography method was a better way to fabricate polycrystalline mercuric iodide array detector than using mask method.

Photoconductive effect based on femtosecond laser pulses to generate terahertz (THz) pulses has been analyzed, and broadband THz radiation has been detected effectively by using the free space electro-optic sampling (FE-EOS). Furthermore, THz pulses generated by the home-made photoconductive antenna and transmitted through the air have been detected by the THz time domain spectroscopy (THz-TDS) system, and the influences under different conditions employed on photoconductive antenna for THz generation have been measured and discussed.

A novel two-dimensional (2D) square lattice Electromagnetic Bandgap (EBG) structure, including EBG waveguide transmission line, quarter turn, and power-divider, operated at the center frequency of 0.5THz is proposed. Finite element method (FEM) was used to analyze and simulate the EBG structure and these components based on EBG. These components were also compared with traditional ones. Simulation and analysis results show that when the radius of Si-wire satisfied the condition: R = 0.4a , where a is the lattice constant, the insertion loss and voltage standing wave ratio (VSWR) of EBG waveguide transmission line and quarter turn are less than -0.05 dB/mm and 1.1, respectively. Meanwhile, the asymmetric division ratio of power divider is better than 0.1 dB. The square lattice has unique advantages in the waveguide transmission line design. The 2D EBG structure can be achieved by using poly-silicon based on MEMS technology with benefits of low loss, planar structures, and high processing accuracy. In addition, it is also easy to integrate with other devices and circuits, such as antennas, filters, diodes, mixers and so on. Hence, this novel EBG structure should have many applications for THz passive components, feed system of antenna array, and integration with other MMIC devices.

In the snowy areas of Northern provinces in China, the cleaning-snow vehicle has to work in the environment of snow blowing and low-visibility. In order to protect the vehicle and driver from obstacles, the millimeter-wave radar was fixed in the cleaning-snow vehicle to give early warning. An efficient moving objects detecting and tracking method was proposed, which employs the average filter and the concept of "lifecycle of object". The average filter is used to solve the problem of the data's abrupt change due to the complex driving condition. The "lifecycle of object" algorithm is exploited to check the validity of objects and eliminate the illusive alarm. The field experimental results show that our proposed method are effective and can achieve good results.

The research on terahertz (THz) fields exists for decades of years, because of its promising applications in imaging, medical diagnosis, security inspection, information communication, etc. There are many ways to generate THz pulses, such as photoconductive effect, optical rectification, photomixing, and so on. For the detection of THz pulses, two methods, free space electro-optic sampling (FS-EOS) and photoconductive (PC) sampling, can be normally used. In our previous experiments, the photoconductive effect has been utilized to generate THz radiation from a piece of semiconductor with antenna structure. The amplitude of THz signals was found to be proportional to the magnitude of the electric field. To understand this more clearly and try to get better THz signals, simulation analysis of the electric field in between the electrodes of the photoconductive antenna has been done, and a optimized antenna structure which will be more efficient than the parallel dipolar electrodes has been designed based on the simulation analysis.

Stepped frequency pulses can be applied in Terahertz radar system, which has been proven by simulation. The stepped frequency THz radar can provide centimeter accuracy. The theory of stepped frequency pulse imaging is introduced, and the model is set up. According to the range-doppler algorithm, some results can be got. At last, The THz imaging system is designed.

We investigate the conduction intersubband linear response of a n-type quantum well driven by one or two infrared optical fields with arbitrary strengths. The fields couple the third subband to the second energy subband and the ground subband, forming a Λ system. We investigate the dependences of the absorption spectrum on the pump field strengths. The results for the equal Rabi frequencies can be understood in terms of quantum coherence processes of the intersubband transitions, such as coherent population trapping, and electromagnetically induced transparency. The effects of different Rabi frequencies on the absorption spectrum due to fields are also discussed.

THz-TDS are used to study four kinds of drug: cortisone, hydrocortisone, prednisone and prednisolone. The THz spectra of them are obtained and analyzed from 0.2 - 1.6 THz. The experimental results shows the four samples have the different THz spectra. Cortisone has a peak at 1.5 THz and a broad absorption peak at 0.96 THz, while hydrocortisone has a weak absorption peak that lies at 1.27 THz. At the same time the prednisone has the stronger absorption peaks than the others, and its two peaks shows at 1.24 THz and 1.5 THz. Prednisolone has a weak broad peak at 1.43 THz. The results of the theoretical calculation were performed using Gaussian 03 software with Density Functional Theory at the basis set of 6-31+G (d, p). The theoretical vibrational frequencies are compared with the experimental results, and the deviations are discussed. The THz spectra of the medicine show THz technique may be help to distinguish some different chemical bond and functional group.

Though a bolometer or calorimeter is often used as the detector in a CW THz imaging system, they are inconvenient or time consuming. Whereas a pyroelectric detector is highly desirable for that it can detect CW THz signals with sufficient speed. In this letter, a THz wave detector based on an infrared pyroelectric senor and its application in CW THz imaging are demonstrated. A responsivity of over 1200V/W at 1.89THz with the modulation frequency of less than 30Hz is achieved, and the peak signal to noise ration (SNR) is estimated to be 38dB. With this homemade THz detector and CW optically- pumped THz laser (OPTL), applications of CW THz imaging are investigated, and a spatial resolution of about 0.3mm is presented.

Transmission characteristics and mode structure of both metal hollow fiber and dielectric-coated metal hollow fiber for terahertz wave are studied. Theoretical evaluation shows that the TE11mode is dominant in metal hollow fiber and has high coupling efficiency when a linearly polarized light source is launched. HE11mode is mainly supported in dielectric-coated metal hollow fiber with an optimum thickness for the dielectric film. The transmission loss of the TE11and HE11mode is8.4dB/m and 2dB/m respectively at the wavelength of 200μm for the hollow fibers with 1mm bore size. The effects of optical constants of metals and dielectric materials on attenuation coefficient are also discussed to optimize the transmission performance of dielectric-coated metal hollow fiber.Aluminum is the best choice among the commonly-used metals based on published optical constants. The optimum value for the refractive index of the dielectric film is1.41. According to the primary measuring results, polyethylene is a proper choice as its refractive index is1.51and it brings low absorption in terahertz waves. The use of Dielectric-Coated Metal Hollow Fiber Bragg phase-shifted fiber grating, for optical fiber and metal combine downhole drill pipe deformation temperature and strain detection underground. Phase-Shifted Fiber Bragg Grating using photoelectric heterodyne detection frequency, the frequency range up to 10¹²Hz, the frequency resolution of 1KHz. LPFG, photovoltaic devices and microwave heterodyne frequency meter combination can solve the phase-shift grating sensor speed and resolution issues.

Unlike traditional THz imaging system, we first report a design of 0.2THz stepped frequency radar system, and prove its feasibility by simulation. The stepped frequency radar working from 200GHz to 210GHz can provide centimeter accuracy. To demonstrate the feasibility of our design, we simulate our system by using Advanced Design System (ADS) and Simulink in Matlab. The transmitter line is simulated in ADS, while system-level simulation is carried out in Matlab. The simulation of transmitter is implemented by using parameters from actual products, which can ensure the reality of simulation. In this paper, we will present the methods and results of our simulation. From the results, we can conclude that our design is feasible.

X-ray grazing incidence supermirror which has extremely broad reflection band is a kind of multilayer with different each layer thickness down through the structure. The x-rays with different wavelengths or at different grazing incident angles can be reflected at different position in the supermirror structure and its band or angular response thus can be extended. These supermirrors have been developed and applied widely in many fields, especially in astrophysics. Existing approaches for designing similar neutron supermirrors are shown to provide respectable performance when applied to x-ray multilayers. However, none of these approaches consider the effects of imperfect layer interfaces and absorption in the overlying layers and all of them insist on the structure with the ratio of the layer thickness of absorbing material to the bi-layer spacing being a constant of 0.5. Adaptations of neutron designs that take these effects into account are presented in the present paper. In addition, other approaches, such as the method based on the combination of analytical and number methods, also are included and discussed in this paper. Two kinds of supermirrors with broad photon energy band or broad angular response have been designed using these different design methods. The results show that for specific applications, different optimization methods with different initial structures should be chosen accordingly to expect some overall improvement on performance of x-ray supermirrors.

High-speed photon counting is useful for discriminating photon energy and for decreasing absorbed dose for patients in medical radiography, and the counting is usable for constructing an x-ray computed tomography (CT) system. A photon-counting x-ray CT system is of the first generation type and consists of an x-ray generator, a turn table, a translation stage, a two-stage controller, a multipixel photon counter (MPPC) module, a 1.0-mm-thick LSO crystal (scintillator), a counter card (CC), and a personal computer (PC). Tomography is accomplished by repeating the linear scanning and the rotation of an object, and projection curves of the object are obtained by the linear scanning using the detector consisting of a MPPC module and the LSO. The pulses of the event signal from the module are counted by the CC in conjunction with the PC. The lower level of the photon energy is roughly determined by a comparator circuit in the module, and the unit of the level is the photon equivalent (pe). Thus, the average photon energy of the x-ray spectra increases with increasing the lower-level voltage of the comparator. The maximum count rate was approximately 20 Mcps, and energy-discriminated CT was roughly carried out.

We report the research results on Solid-State Laser System for Terahertz Radiation Generation. Terahertz radiation generation is based on a double longitudinal mode laser with a single linear cavity and laser amplifiers. The laser is LD pumped CW Nd:YVO4 laser with a single linear cavity. The double longitudinal mode laser beam makes it very convenient to control their propagation for Terahertz radiation generation. The relative intensities of the modes and the frequency difference between the modes can be adjusted for high efficiency generating THz radiation with required frequency. The CW laser beam was first amplified by a LD end-pumped Nd:YVO₄ amplifier, then it was changed into pulsed beam by an LN electro-optical modulator. The pulsed laser beam was amplified by other four Nd:YVO4 amplifiers pumped by three 6W LDs and a 35W optical fiber coupled LDA, respectively, and became strong enough and was projected into an organic nonlinear optical crystal DAST to generate THz radiation with narrow linewidth and stable frequency. By this method a new kind of THz wave source can be developed. It is smaller in size, high efficient and no any adjustment is needed in applications. The paper reports the experimental setup and results in details.

We use terahertz time-domain spectroscopy (THz-TDS) to measure the absorption spectra of six drugs, atenolol, furosemide, tropicamide, lobeline hydrochloride, propranolol hydrochloride, and promethazine hydrochloride, in the frequency range of 0.3 THz to 2.0 THz. Furosemide, tropicamide, and promethazine hydrochloride show distinct absorption features, whereas atenolol, lobeline hydrochloride, and propranolol hydrochloride exhibit no obvious absorption peaks. The use of THz-TDS makes it possible to rapidly distinguish the drugs with characteristic absorption peaks. Our results demonstrate that THz-TDS is highly sensitive to the structure and spatial arrangement of molecules. As a result, THz-TDS will have potential exploitation in pharmaceutical fields.

A dual energy X-ray detector for conveyor belt with steel wire ropes is researched in the paper. Conveyor belt with steel wire ropes is one of primary transfer equipments in modern production. The traditional test methods like electromagnetic induction principle could not display inner image of steel wire ropes directly. So X-ray detection technology has used to detect the conveyor belt. However the image was not so clear by the interference of the rubber belt. Therefore, the dualenergy X-ray detection technology with subtraction method is developed to numerically remove the rubber belt from radiograph, thus improving the definition of the ropes image. The purpose of this research is to design a dual energy Xray detector that could make the operator easier to found the faulty of the belt. This detection system is composed of Xray source, detector controlled by FPGA chip, PC for running image processing system and so on. With the result of the simulating, this design really improved the capability of the staff to test the conveyor belt.

Planar integrated antenna has special advantages in Terahertz application, but with disadvantage of low gain. In this paper, a novel Terahertz integrated horn antenna operating at 0.9 THz was proposed in order to enhance the radiation performance of planar integrated antenna elements. The processing of this type horn antenna combine two kind MEMS techniques, silicon dry etching and silicon wet etching. The structure of the horn includes two parts, pyramid horn back cavity and octagonal horn front cavity. FEM (Finite Element Method) is used to analyze the performances of antenna. The main superiority of this kind integrated horn antenna is that it has more tunable parameters than other type MEMSbased integrated antennas. High performance Terahertz antenna elements can be obtained by synthesizing the parameters of the horn.

The terahertz wave transmission through ensembles of sub-wavelength size metallic particles is studied by THz-TDS and finite different time domain (FDTD). The result of the experiment shows that with the increase of the thickness of the sample, the terahertz pulses experience significant attenuation, delay and broadening. In addition, an obvious red-shift and narrowing of the amplitude spectrum are observed. Numerical simulations based on FDTD are performed to explain the details of the data and lead to an excellent agreement with the experimental results. Furthermore, the relation between the size of the particles and the transmission properties of terahertz radiation is analyzed.

This paper proposes a novel single-poly floating gate (FG) UV sensor in standard CMOS process. The sensor cell is based on PMOS FG and only adopts four transistors including sensitive component and readout amplifier. The architecture is compact and feasible for future high density array chip implementation. A theoretical analysis of sensor sensitivity is described in detail. As the sensor is compatible with standard single poly CMOS process, it has the merits of low cost, more sensitive, and be integrated with signal processing system. A prototype chip is manufactured in a 0.18μm single-poly standard CMOS logic process. The tested results indicate that the sensor is sensitive to the incoming UV irradiation.

After presenting all kinds of calibrating methods to calibrate the magnitude response and risetime of the digital oscilloscope, this paper describes the method that by using femto-second laser pulse to illuminate high-speed photo-detector ultra-fast electrical pulses with only 10ps risetime which are supposed to calibrate the oscilloscope can be generated. In experiment the 12GHz real-time digital oscilloscope has been calibrated successfully. This method has some advantages such as simple structure, convenience in using and great application potential.

In this article, we report the two terms Laser Compton Scattering (LCS) via interaction experiments at 100 MeV linear accelerator of SINAP. The monochromatic X-rays were generated by a 108.1 MeV, 2.5 ns electron beam colliding with two Nd:YAG lasers of 113mJ/pulse,35 ns and 2J/pulse, 10 ns, respectively, and demonstrate the latest developments in construction of experimental facilities at SINAP: a high-intensity ultrafast laser and electron interaction experimental facility based on Shanghai Deep Ultraviolet-Free Electron Laser (SDUV-FEL) device. In addition, we present a future Laser Compton Scattering (LCS) γ-ray source - Shanghai Laser Electron Gamma Source (SLEGS) at Shanghai Synchrotron Radiation Facility (SSRF) is presented. It is one of beamlines of SSRF in Phase II and will be finished around 2011. Key words: Laser Compton Scattering (LCS); Shanghai Laser Electron Gamma Source (SLEGS); 100MeV & 150MeV Linac; Shanghai Synchrotron Radiation Facility (SSRF);

The scanning imaging system has low frame rate due to the long period of point-by-point scanning especially for the large-sized object, while the array imaging system with relatively high frame rate is employed to image for small-sized objects due to the limit of the detector size. In this paper, a novel imaging system applying the scanning imaging setup and a 124×124 array detector is constructed and the software based on Visual C++ is designed to control the scanning process, collect image data, display the imaging result and the image mosaic process, and store the complete image. Utilizing the 2.52-THz laser generated by the SIFIR-50FPL as the imaging light source, preliminary imaging experiments are done. The imaging results are basically clear and image stitching effect is comparatively satisfying. Comparing with the point-by-point scanning imaging system, the frame rate is improved. Comparing with the array imaging, the setup is able to image for large objects utilizing the scanning system.