This PDF file contains the front matter associated with SPIE Proceedings Volume 8909, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.

In recent years, the micro-Doppler effect has been proposed as a new technique for signature analysis and extraction of radar targets. The ballistic missile is known as a typical radar target and has been paid many attentions for the complexities of its motions in current researches. The trajectory of a ballistic missile can be generally divided into three stages: boost phase, midcourse phase and terminal phase. The midcourse phase is the most important phase for radar target recognition and interception. In this stage, the warhead forms a typical micro-motion called micro-nutation which consists of three basic micro-motions: spinning, coning and wiggle. This paper addresses the issue of signature analysis of ballistic missile warhead in terahertz band via discussing the micro-Doppler effect. We establish a simplified model (cone-shaped) for the missile warhead followed by the micro-motion models including of spinning, coning and wiggle. Based on the basic formulas of these typical micro-motions, we first derive the theoretical formula of micro-nutation which is the main micro-motion of the missile warhead. Then, we calculate the micro-Doppler frequency in both X band and terahertz band via these micro-Doppler formulas. The simulations are given to show the superiority of our proposed method for the recognition and detection of radar micro targets in terahertz band.

Considering the overmoded structures of high-power Terahertz(THz) sources are often electrically large, it’s difficult to compute the radiation of THz antennas on a personal computer due to over long time and prohibitive computation resources. A parallelized finite-difference time domain (FDTD) algorithm based on MPI platform and virtual topology structure, combined with theory of guided waves, is presented for analysis of the radiation of the large THz conical horn excited by mixed-mode souce. Cartesian virtual topology structure is firstly defined by MPI_CART_CREATE( ) function based on MPI platform. And MPI_CART_SHIFT() function is used to define the position relations of the subdomains. Then FDTD method is used in each subdomain. The absorbing boundary of the whole FDTD domain is uniaxial perfectly matchedlayer (UPML), and that of the waveguide is convolutional PML(CPML). Synchronous communication mode is used in parallelized FDTD between the adjacent subdomains. The coefficient of field components for each mode source can be got based on the given power of each mode. Thus the mixed-mode excitation source can be set by the coefficient and each mode’s initial phase. Examples of an electrically large THz horn with 4 or 6 modes mixed excited are given in this paper. Considering the universal characteristic of FDTD method, the method shown in this paper can be used to simulate the radiation of other kinds of THz antennas with mixed-mode exicitation source. And it’s useful for the design of those structures.

The transmission characteristics of cylinder and rectangular metal overmoded waveguides frequently used in 0.14 THz frequency band are numerically studied in this paper. At first, skin depths and losses of overmoded cylinder waveguides for different waveguide materials and terahertz wave modes are theoretically calculated and validated by electromagnetic finite difference time domain (FDTD) method. Loss as high as 5 dB/m is obtained for stainless steel and TM01 mode, and it increases with mode orders and decreases with waveguide radius. Also the mode conversion is observed in the straight overmoded cylinder waveguide with finite conductivity. Then transmission characteristics of overmoded rectangular metal waveguide including bend waveguides, straight waveguides, and transition waveguides are researched. The significant mode conversions in the overmoded E and H bend waveguides are found even ignoring the effect of finite conductivity. Only a few of the TE10 mode within frequency band of 0.13-0.16 THz is successfully transported through the standard bend waveguides in Ka band. The transmission characteristics of overmoded straight rectangle waveguide are almost the same as the cylinder one’s. Non-cutoff modes for the two waveguides connected by transition waveguide can transfer through it without losses, while the rest modes can’t.

This paper has successfully setup a calibration system for terahertz devices at frequencies from 0.11 THz to 0.17 THz in waveguide WR6.5. The system consists of a terahertz wave generator, a power meter, a digital oscilloscope and a computer, and is able to accomplish calibrations for some devices automatically. Calibrations of a 10 dB attenuator, a 20 dB directional coupler, and a Schottky diode detector are carried out by the system and a detailed discussion is given to the results. The results obtained have shown that the characteristics of the devices under calibrated remained essentially the same throughout the experiment and met rather good agreement to the factory data. Due to the use of GPIB, it is proved that the system can also improve the efficiency of work greatly. The calibration approach described in this paper can be a necessary supplement to the other calibration techniques and play an important role in terahertz measurement especially at lower frequencies.

Our recent important progress in terahertz (THz) functional devices based on photonic crystals and plasmonics was reviewed in this paper, involving THz modulator, isolator and sensor. For THz modulators, we demonstrate the transmission and modulation properties of a state conversion photonic crystals and a metal-semiconductor-metal plasmonic waveguide based on theoretical and experimental investigations. We also show the nonreciprocal transmission and enhancement mechanism of the structured metal/magneto-optical plasmonic waveguide and plasmonic lens for THz isolator and circulator. Moreover, a real-time quantitative THz microfluidic sensing based on photonic crystal pillar array is introduced by experimental results. These THz functional subwavelength devices exhibit great promising potential in THz application systems.

An integrated 0.5 THz electromagnetic crystals(EMXT) channel-drop filter based on PBG structure is presented in this paper. A channel-drop filter is a device in which a narrow bandwidth is redirected to another “drop” waveguide while other frequencies are unaffected. It’s capable of extracting a certain frequency from a continuous spectrum in the bus channel and passing it to the test channel. It has potential applications in photonic integrated circuits, radio astronomy, THz spectroscopy, THz communication and remote sensing radar receiver. PBG structures(or photonic crystals) are periodic structures which possess band gaps, where the electromagnetic wave of certain ranges of frequencies cannot pass through and is reflected. The proposed channel-drop filter consists of input waveguide,output waveguide and PBG structure. The proposed filter is simulated using the finite element method and can be fabricated by micro-electromechanical systems (MEMS) technology,due to its low cost, high performance and high processing precision.The filter operation principle and fabrication process are discussed.The simulation results show its ability to filter the frequency of 496GHz with a linewidth of approximately 4GHz and transmission of 27.2 dB above background.The loss at resonant frequency is less than 1dB considering the thickness and roughness of gold layer required by the MEMS process.The channel drop efficiency is 84%.

This paper presents a new method about 0.14THz power divider based on 3 dB directional coupler. As THz device’s dimension is micro-miniature, especially the key structure such as power divider’s, it is extraordinary difficult to fabricate by precise machining. Traditional 3dB directional coupler has 90° electric bridge structure, whose length between coupler slots is only less than 0.5mm. This size nearly cannot bear the machining stress in processing. By means of analyzing the phase relationship between the direction coupler’s branches, it is known that if the length between coupler slots increases only half-wave length’s integermultiple, the phase contrast between branches is still 90°. As a result, the bandwidth is sacrificed. Since the dimension of coupling slot increases, this structure makes precise machining easy, and it has a band width about 10% at least yet. Analysis of simulation result provides the verification. The measured insert loss from 0.133THz to 0.147THz is less than 1dB, and the return loss is less than -20dB.

A metal hole arrays terahertz filter based on surface plasmon polaritons and fabricated by aluminum slab of different holes scales have been experimentally investigated by using THz time-domain spectroscopy system from 0.1 to 2.7 THz. The experiment results indicated there is a transmission peak at 0.26 THz, approximately. The results in simulation by finite element method agree well with the experimental one for the big scale sample. The mismatch of experimental and simulated results for small scale sample can be attributed to boundary condition and insufficient periodical extension. Further, the theoretical analyses about extraordinary optical transmission and filter phenomena are also discussed.

This paper puts forward a newer sensor which is symmetrical two rectangular resonant cavities based on parallel-plate waveguide, using the lowest-order transverse-electric mode in terahertz region . From the simulation result we found when we place the material in one of the resonant cavity, the original symmetric state has changed, not only a new resonance peak appear ,but it also every resonant peak has obvious relative frequency shift with different material. So the structure can be used as the sensor, which can detect the material.

In the calculation of the rough surface, one of the methods to establish the model is to view the rough surface as a plate with hemispherical bosses. Thus the calculation of a hemispherical boss becomes a part of the simulation of the rough surface. With the development of radar technology, the requirement of the radar cross section (RCS) becomes higher, which makes the measurement and calculation of the terahertz RCS become more important. However, due to the different energy distribution between the Gaussian beam and plane wave, the simulation results would exist some error when assuming that the incident beam is a plane wave. In this paper, the method of images is utilized to calculate the RCS of a hemispherical boss at 2.52 THz when the incident beam is Gaussian beam and the results are compared to that calculated when the incident is plane wave.

FSS is a two-dimensional periodic array of resonating metallic-dielectric structures, When FSS device steps into Terahertz range from microwave range, it is studied as THz functional components (such as Terahertz filter, Terahertz biochemical sensor, etc.) to promote the functionality of the THz spectroscopy/imaging system. When the device requires a narrow band transmission window for frequency selecting or a high electric field concentration in certain area to improve its sensitivity for sensing, normally, a high quality (Q) resonant structure can give helps. Recently, high-Q resonance induced by trapped mode resonance i studied widely in FSS research areas. To induce trapped mode resonance, one can simply break the symmetric of the unit structure of FSS. In this paper, several asymmetric X-shaped resonators for FSS working in terahertz range have been studied numerically. To compare the behaviour of X-shape resonator under different conditions (with additional part: Heart lines, Shoulder lines, Wrap or Shoes squares), a common platform (θ=60, θis angle of X shape) which is suitable for most of cases was used to make the study more meaningful. As the field enhancement behaviour is related to the trapped mode introduced by the asymmetric structure, we propose such kind of device to be used as a high quality filter or as a sensing element for biochemical samples.

Localized plasmon modes are excited and probed in a large-area grating-gate GaN/AlGaN high-electron-mobility transistor structure embedded in a Fabry-Pérot cavity using a terahertz time-domain spectroscopy (THz-TDS) at cryogenic temperature. Determined by the length of grating finger and the electron concentration, the frequency of localized plasmon modes can be continuously tuned by the gate voltage in the spectral range from 0.1 THz to 1.5 THz. When the plasmon frequency is tuned to be in resonance with the terahertz Fabry-Pérot cavity mode, a strong coupling between the plasmon mode and the cavity mode is observed and the terahertz plasmon-polaritons are formed in such a cavity-coupled two-dimensional electron system. The electromagnetic simulations have confirmed the strong coupling between them.

The characterization of the emission of terahertz (THz) waves generated by four-wave mixing in the presence of laser-induced air plasma under different pump power is presented. In our experiment, terahertz is detected using THz Air-Biased Coherent Detection (THz-ABCD) method. Red-shift is observed in frequency spectra with enhanced pump power and the bandwidth is narrowing down. Then the localized terahertz radiation along the plasma was studied, by constricting the emission area with a pinhole. The spatio-frequency dependent of THz emission from laser-induced air plasma is observed. These phenomena are explained by intense self-phase modulation of the optical pulse in the plasma. This study reveals that terahertz spectrum can be controlled by changing the pump power to get useful frequency range.

A novel invisible media based on transformation optics consisting of three regions to investigate invisibility was proposed here. What the media does is to compress the light to a small region so that the light can avoid interacting with objects, and then it would be recovered in the latter. Comparing with the traditional cylinder cloak, which require the light propagating around the concealed region, the media would help us to avoid singularity of material parameters. Finite element simulations for two-dimensional cases have been performed to prove these ideas.

A terahertz one-dimensional photonic crystal (PC) cavity with high Q-factor is demonstrated theoretically and experimentally. The cavity consists of two parallel distributed Bragg mirrors and one air layer between them as defect layer. By increasing the length of the defect layer, the cavity has a very narrow transmission bandwidth (FWHM) of 30MHz at resonant frequency of 336GHz, i.e. a high Q over 1.1×10⁴ is achieved. What's more, an optically controllable THz switch is demonstrated by light irradiating on one of the middle silicon wafer in the cavity, the optical beam power needed for the switch is remarkably reduced to 0.16 W/cm², which is nearly 50 times smaller than that for a THz switch using a single silicon wafer. Finally, such high Q cavity is very sensitive to the refractive index change in the cavity, it is suitable to be used in gas sensing. The experimental results verified its applications in H₂, N₂, and CO₂ gas detections.

In this paper, we deployed a home-made THz time-domain system and experimentally investigated the influence of impairment on photoconductive antenna. The low temperature grown GaAs photoconductive antenna (PCA) was used as THz emitter and a <110< ZnTe crystal modulating the probe beam to detect the THz field based on electro-optic sampling. By adjusting the position of laser spot on PCA gap, we found that the generated THz signal was quite different as the laser beam irradiating on different position of the antenna’s gap. Moreover, we found that the small burned holes on the edge of both metal electrodes may affect the electric field of the antenna. Furthermore, we simulated the electric field of the PCA with a DC biased voltage applied across the electrodes, and found that the simulation results agreed with the experimental phenomenon, which can well demonstrated that the impairments on the antenna electrodes have a great influence on THz generation.

Passive terahertz imaging technology, which provided blackbody thermal imaging, showed great potential for security applications during the last years. Different research teams in different countries spent a great effort on it for obvious reasons, and first commercial passive THz human imaging system was available. Yet, development of passive THz-imaging system was always limited by the frame rate, spatial resolution and detector cell of it. In this paper, we presented the concept and experimental set-up for a quasi-optical system used in a near-field 0.14THz passive terahertz imaging system. The quasi-optical system was composed of a double-mirror beam-waveguide system and a special feed-horns array. The design of quasi-optical system was based on near-field Gauss optics theory. The double-mirror beam waveguide system was made up of an off-axis ellipsoid mirror and a flat mirror. The influence of angle-scanning of quasi-optics system in near-field THz-imaging was investigated theoretically. Meanwhile, a spatial sparse array-arrangement of feed-horns was applied in quasi-optics system, that the adjacent feed-horns were stagger in the horizontal direction. The influence of this special feed-horns array arrangement on the near-field imaging was also discussed in theory. The quasi-optical system met the requirements of the near-field imaging. The problem of low frame rate of traditional sparse array arrangement was solved by this special array arrangement. And the spatial imaging range of the passive imaging system was also increased. The experimental results of this terahertz imaging system were consistent with our earlier theoretical results. When the detective distance was 3-5m, the experimental spatial resolution of near-field THz imaging was 5cm, and a 5Hz of frame rate was obtained. The quasi-optics system had demonstrated its ability to scan persons and various kinds of objects. We hoped a commercial, user-friendly terahertz imaging system, which could be used for security purposes, would be achieved in the future. And as a beginning step towards this goal, our theoretical and experimental results would be the basis of the improvement of near-field passive terahertz imaging system.

Recently, Silicon nanowires(Si NWs) have been suggested as a promising candidate for solar energy harvesting. The Si NWs have the advantage of enhancing the optical absorption for broadband spectra, which increases the optical absorption significantly. It is of crucial importance for high efficiency solar cell. We applied the transient optical-pump THz emission spectroscopy to research Si NWs fabricated by chemical etching and to analyse the THz radiation mechanism. The experiment datas indicated that Si NWs enhance the optical absorption significantly. And the lifetime and dynamics properties of photoexcited carriers are important to the photovoltaic conversion efficiency of solar cell. Here the optical-pump terahertz-probe system was employed to study the ultrafast dynamics and transport properties of photoexcited carriers in Si NWs. The experiment results shown that carrier lifetime in Si NWs is approximate 0.7ns, and it reduces optical energy-conversion efficiencies of solar cell. However, compared to other silicon nanostructures, Si NWs fabricated by chemical etching have relative high values for both the carrier lifetime and mobility. The detailed analysis of the optical absorption and carriers dynamics would be significant for optimizing configuration of the silicon nanostructures.

Absorption spectra of chiral S-(+)- and racemic RS-ketoprofen pharmaceutical molecules in crystalline form were recorded in the terahertz region between 6 and 66 cm^-1 (0.2 ~ 2.0 THz) by using time-domain terahertz spectroscopic (THz-TDS) measurement. Different distinctive absorption features were observed which are strikingly sensitive to the change of subtle conformational structures within such isostructural crystal molecules. The results suggest that the THz-TDS technique can be definitely used for distinguishing between chiral and racemic compounds in pharmaceutical and biological fields.

This paper discusses the development of data acquisition and control system (DACS) for a portable terahertz time-domain spectrometer (THz-TDS). In this system, field programmable gate array (FPGA) severed as main control unit (MCU), which controls and harmonizes other functional modules of the spectrometer, including the linear delay stage, high voltage modulation and the AD converter. A digital lock-in amplifier implemented within the FPGA is employed to restore the weak THz signal. USB is used as the communication interface between the FPGA and the computer, which transfers commands and THz waveform data. The spectrometer can scan a waveform within a 30-ps time window in about 10 seconds, which has a spectral resolution better than 50GHz and a dynamic range up to 49dB.

Continuous-wave (CW) terahertz (THz) imaging system has advantages of high power, compact structure and low cost, thus having been investigated for widespread applications. In typical reflection mode of CW imaging, the obtained image is usually degraded by repeated fringes, which is caused by interference phenomenon. The undesired interference signal originates from the reflection of surfaces of samples and lenses. When the samples are titled placed or their surfaces are uneven, the detected signal intensity is fluctuant even if the same sample lies in different positions. Therefore, small-sized or weekly absorbing objects are hard to be distinguished. Based on cartoon-texture decomposition, we propose a practical method to restore CW THz reflection images. After decomposition, the fringes and the objects are separated. In order to preserve edges, sharpening and fusion steps are employed respectively. The object in the final image is obvious with little loss of information.

We theoretically demonstrate a switchable metamaterial with dual-mode resonance located at THz regime under normal incidence by reshaping metamaterial elements. The mode switching allows easily controlling the resonant absorption of the metamaterial from 0.49 THz to 0.53 THz, and from 1THz to 1.13THz, precisely. Such switchable dual mode metamaterial promises wide application in optical switches, tunable filter, and THz detectors.

There has been intense interest in the use of millimeter wave and terahertz technology for the detection of weapons, explosives and other threats. System based on electromagnetic radiation between 30 GHz and 3 THz have advantages that radiation penetrates many common materials, wavelengths are short enough to give adequate spatial resolution and radiation at these frequencies is safe to use on people. It is also applied to the retrieval of tropospheric parameters with the ground-based radiometer system. Tropospheric temperature, humidity and cloud liquid water are key elements in meteorology. Since the 151 GHz channel strongly depends on cloud liquid water, the retrieval accuracy of atmospheric parameters is improved by the inclusion of a channel at 151 GHz. The new retrieval model which uses 123 GHz, 127 GHz and 168 GHz is proposed. Simulations of retrieval are presented based on the radiosonde dataset of Beijing China and the retrieving errors of different methods are compared.

The passive detection is safe for passengers and operators as no radiation. Therefore, passive terahertz (THz) imaging can be applied to human body security check. Imaging in the THz band offers the unique property of being able to identify object through a range of materials. Therefore passive THz imaging is meaningful for security applications. This attribute has always been of interest to both the civil and military marks with applications. We took advantage of a single THz detector and a trihedral scanning mirror to propose another passive THz beam scanning imaging method. This method overcame the deficiencies of the serious decline in image quality due to the movement of the focused mirror. We exploited a THz scanning mirror with a trihedral scanning mirror and an ellipsoidal mirror to streamline the structure of the system and increase the scanning speed. Then the passive THz beam scanning imaging system was developed based on this method. The parameters were set as follows: the best imaging distance was 1.7m, the image height was 2m, the image width was 1m, the minimum imaging time of per frame was 8s, and the minimum resolution was 4cm. We imaged humans with different objects hidden under their clothes, such as fruit knife, belt buckle, mobile phone, screwdriver, bus cards, keys and other items. All the tested stuffs could be detected and recognized from the image.

This paper designs a two-dimensional (2D) photonic crystal based THz bandpass filter (BPF). Fine bandpass property is realized by introducing symmetrical point defect on both sides of a line defect 2D photonic crystal to the forming of resonant cavity. This kind of 2D photonic crystal filter has large bandwidth and its out-band rejection properties can be further improved by introducing more pairs of symmetric point defects to realizing the cascading of more resonant cavity. The designed filter can satisfy application needs in THz communication and radar systems.

The terahertz absorption spectrum of explosive materials can be measured by terahertz time domain spectroscopy operated in transmission mode. In this paper, the absorption characteristics of four explosive materials in spectral range of 0.1–3 THz are studied. It shows that even for the same materials, the spectral absorption peak value in the same measurement condition is a little different. So the measurement precision of the terahertz time domain spectroscopy is very important for the feature extraction and identification of explosive materials. This work investigates the measurement precision of terahertz time domain spectroscopy. Some factors that affect the measurement precision of the terahertz time domain spectroscopy are analyzed and discussed.

We investigate the ISAR imaging in background noises by using the analytical solutions and physical optics within the terahertz region. When increasing the frequency band wide, the scattering signals of the metal sphere are enhanced by the coherent measurement technique, and the background noises are effectively canceled. Furthermore, the resolution of SAR imaging is improved to precisely locate the scattering centers of objects. However, the increased band wide seemly decreases the contrast of imaging due to the discrete grids of filtered back projection algorithm.

The rapid development of the communication technology and sensing applications calls for broader bandwidth and faster speed. The influence of atmosphere on the propagation character of THz wave can mainly fall into two categories: the scattering of the particles in the atmosphere and the absorption of atmosphere molecules which can be divided into two aspects: line-by-line and continuum absorption. The most controversial point is the calculation of continuum absorption. The specific attenuation of different humidity are calculated by AM model and the modified VVW line shape method and compared with that of ITU-R P.676-9. The continuum absorption of the AM model is calculated using the MT-CKD method, another method to calculate the continuum absorption is to introduce continuum-like terms of water vapor and dry air which is used in the modified VVW line shape method. The result shows a better agreement of the modified VVW line shape method than that of the AM model because the coefficient can be modified to fit the ITU-R P.676-9, and the difference between the AM model and the ITU-R P.676-9 is small, too. The best fit coefficients of modified VVW line shape method for different humidity are obtained. And the relation of the coefficients and the humidity can be expressed by two regressed equations, and the humidity modification is included in the new correction terms.

Terahertz spectroscopy is a powerful tool for materials investigation. The low frequency vibrations were usually investigated by means of absorption coefficient regardless of the refractive index. It leads to the disregard of some inherent low-frequency vibrational information of the chemical compounds. Moreover, due to the scattering inside the sample, there are some distortions of the absorption features, so that the absorption dependent material identification is not valid enough. Here, a statistical parameter named reduced absorption cross section (RACS) is introduced. This can not only help us investigate the molecular dynamics but also distinguish one chemical compound with another which has similar function-groups. Experiments are carried out on L-Tyrosine and L-Phenylalanine and the different mass ratios of their mixtures as an example of the application of RACS. The results come out that the RACS spectrum of L-Tyrosine and L-Phenylalanine reserve the spectral fingerprint information of absorption spectrum. The log plot of RACSs of the two amino acids show power-law behavior σ_R(^~ν) ∝ (ν^~α), and there is a linear relation between the wavenumber and the RACS in the double logarithmic plot. The exponents α, at the same time, are the slopes of the RACS curves in the double logarithmic plot. The big differences of the exponents α between the two amino acids and their mixtures can be seen visually from the slopes of the RACS curves. So we can use RACS analytical method to distinguish some complex compounds with similar function-groups and mixtures from another which has similar absorption peaks in THz region.

The terahertz region of the electromagnetic spectrum spans the frequency range of 0.1THz~10THz, which means it sandwiches between the mid-infrared (IR) and the millimeter/ microwave. With the development and commercialization of terahertz pulsed spectroscopy (TPS) and terahertz pulsed imaging (TPI) systems, terahertz technologies have been widely used in the sensing and imaging fields. It allows high quality cross-sectional images from within scattering media to be obtained nondestructively. Characterizing the interaction of terahertz radiation with multilayer medium structures is critical for the development of nondestructive testing technology. Currently, there was much experimental investigation of using TPI for the characterization of terahertz radiation in materials (e.g., pharmaceutical tablet coatings), but there were few theoretical researches on propagation of terahertz radiation in multilayer medium structures. Finite Difference Time Domain (FDTD) algorithm is a proven method for electromagnetic scattering theory, which analyzes continuous electromagnetic problems by employing finite difference and obtains electromagnetic field value at the sampling point to approach the actual continuous solutions. In the present work, we investigated the propagation of terahertz radiation in multilayer medium structures based on FDTD method. The model of multilayer medium structures under the THz frequency plane wave incidence was established, and the reflected radiation properties were recorded and analyzed. The terahertz radiation used was broad-band in the frequency up to 2 THz. A batch of single layer coated pharmaceutical tablets, whose coating thickness in the range of 40~100μm, was computed by FDTD method. We found that the simulation results on pharmaceutical tablet coatings were in good agreement with the experimental results obtained using a commercial system (TPI imaga 2000, TeraView, Cambridge, UK) , demonstrating its usefulness in simulating and analyzing terahertz responses from a multilayered sample.

The optical and dielectric properties of NaCl and alkali halide are studied by Terahertz time-domain spectroscopy (THz-TDS) technique from 0.3 THz to 1.4 THz. The absorption spectral features of measured samples are discussed based on their characteristic and common features. Further, the measured complex refractive index and dielectric functions of NaCl are well fitted by a standard Lorentz model. Theoretical calculations indicate that characteristic phonon resonance of NaCl is dominated by the transverse optical phonon mode at 5.10 THz.

Cherenkov phase-matching terahertz-wave generation is attractive way of efficient THz-wave generation. Efficient THz-wave generation by nonlinear optics has two problems, strong absorption and strong dispersion of many crystals. These problems can be overcome by Cherenkov phase matching. We successfully demonstrated wide tunable monochromatic THz-wave generation about from 0.2 to 7.2 THz using waveguided lithium niobate crystal. The Cherenkov process is useful for novel THz-wave detection method. THz-wave and optical waves in nonlinear optical process are strongly correlated. Thus, THz-wave information can transfer to pump and signal wave. THz-wave generated by Cherenkov phase matching can be used as evanescent-probe at interface facet of the crystal. Phase shift and attenuation of reflected THz-wave has information of a sample set at the interface, so the information can be detected by optical analysis for pump and signal wave.

Based on the characteristics of terahertz wave, the ability of THz for uncovering target covered by camouflage coating is studied. Firstly, the paper introduces the camouflage coating classification and reflectivity. Secondly, a coating reflection characteristic calculation model is established on conditions of smooth surface with methods of matrix optics. Finally, according to the calculation model, the reflectance of infrared coating and laser coating in different wavebands including 337μm terahertz wave was calculated. According to the calculating result, it’s indicated that THz has better ability to penetrate through coating than IR ; meanwhile, it’s also indicated that THz has the ability for uncovering target on some conditions.

Recently infrared photodetectors have attracted much attention due to their potential use in infrared imaging, optical communications, medical detection and many other fields. In this letter, we report a THz quantum well infrared detector based on AlGaAs/GaAs material system. Structure with 4% Al content in the barrier was grown using molecular beam epitaxy (MBE). The photocurrent spectra were measured at 4.3 K with a Fourier transforming infrared spectrometer using a solid substrate far-IR beam splitter and the peak response wavelength at 46 μm was observed, close to the theoretical calculated results. The dark currents for the THz QWIP detector have been measured at different temperatures. It was found that there is a huge discontinuity in the current. We analyzed this phenomenon and believed the discontinuity in the current was caused by intersubband impact ionization of the first quantum well.

This paper reports the fabrication details of ion-implanted Si:P blocked-impurity band photodetectors with lateral structure. A set of performance data has been measured under the operating temperature of 5.5 K. The device exhibits good blocking characteristics with low dark current density under 10⁻⁴ A/cm². Linear black-body response has been observed at small bias voltage (1 V) and low temperature (5.5 K) with the peak responsivity of 0.8 A/W. The photocurrent (PC) spectra show response peak at 27.3 μm and extend to 40 μm (~7.5 THz), which indirectly proves the feasibility of the preparation of Si:P BIB detectors using ion implantation. In addition, other small features in the PC spectra are designated to associate with the photothermal ionization and the silicon phonon absorption processes. Our work provides an alternative convenient approach to fabricate Si:P BIB detector for far-infrared and terahertz radiation detection.

We have demonstrated a light control terahertz modulation system based on the semiconductor material, the system is composed of a commercial 850nm 10Gbps light source and a continuous THz source. The semiconductor device is the epitaxial growth Si layer on Si substrate wafer. When the 850nm light and continuous terahertz waves incident simultaneously to this semiconductor wafer, the modulated light can excite photogenerated carriers. And the carrier determines the absorption of terahertz waves, so the amplitude of output terahertz waves will be modulated. The tested modulation depth is 35%. The semiconductor material carriers lifetime determines both the modulation depth and modulation speed. So the carrier lifetime should be trade off considered. The modulation speed has been theoretical calculated and experimental tested. The carriers lifetime is tested about 2ns, and the modulation speed is calculated beyond gigabit per second.

Terahertz modulation techniques are an indispensable key technique to achieve the future wireless terahertz wave high-speed communication systems. Metamaterials is artificial materials that geometric structure units are embedded in the traditional medium materials. In this letter we will introduce metamaterials terahertz modulation techniques and analyze the advantage and disadvantage of recent research progress in the world, including electrically controlled THz metamaterials modulators, optical controlled THz metamaterials modulators and some new modulators based on material-graphene

The fundamental parameters of THz modulators based on the SRR structure metamaterial have been researched and found that the SRR size and opening width have a significant effect on the resonant frequency, meanwhile the thickness and width of this structure are very weak influence on the resonant frequency. The resonant frequency and response time have been calculated theoretically. The resonant frequency fits the simulation results well, and response time is mainly determined by the carrier lifetime which is in nanosecond order. We also proposed a program of experimental measurements of the SRR modulation speed. Finally we simulated a special SRR structure with metal strips on the back of wafer to increase modulation depth significantly.

In the MEMS fabrication process of 0.345THz micro-electric vacuum FWG-TWT, the periodic FWG slow wave structure is assembled by joining two symmetrical metal pieces with grooves. In ideal design, these grooves’ profiles should be perpendicular to their symmetrical plane while the device’ performance can be best, however those slope angles are actually more than 90 degrees because of their molds’ insufficient exposure. This paper does research on the influence of waveguide’s exposure steepness on the performance of FWG circuit through theoretical analysis and numerical simulation. The range of slope angle studied in this paper is from 0 to 5 degrees, and as the slope angle becomes larger, electromagnetic signal’s transmission attenuation increases. But by adjusting other working parameters of the circuit, the high net gain can be maintained while its bandwidth is going to decrease. These results will be helpful for the experiment.

We have designed a novel uncooled Terahertz (THz) imaging array based microbolometer. The Micro Electro Mechanical System (MEMS) technology is used to fabricate the imaging array which comprise bolometer layer, THz absorption layer, supporting layer (silicon nitride (SiNx)), resonant optical cavity and electrode. The vanadium oxide thin films is selected for the bolometer temperature sensing material because it has a high temperature coefficient of resistance (TCR) in the range 2%/K and 3%/K at room temperature and suitable square resistance 18.40kΩ/□, a small 1/f noise constant and can be integrated with signal read-out electronics in a cost efficient way. In order to provide a high absorption of the radiation in the bolometer membrane, a resonant optical cavity structure which has a reflection layer formed at the bottom of air gap is adopted for the targeted wavelength. The best air gap of the optical cavity structure is quarter of wavelength of interest, for example, 25μm for 3 THz radiation. The absorption mechanism is that the two reflected THz radiations coming from the absorption layer and reflection layer interfere destructively at THz absorption layer and free carriers in THz absorption layer absorb THz radiation, the absorbed THz radiation heats the imaging array so that the resistance values of bolometer change. The microbolometer need to be packaged in vacuum for best performance, so a cylindrical vacuum chamber which is sealed with polyethylene lamina for the THz radiation is fabricated. In order to maintain the vacuum performance of the chamber (conventional bolometers operate with vacuum levels <0.01mbar), the vacuum pump and molecular pump are adopted; furthermore the packaging technique of vacuum chamber is introduced in detail. Finally, because of its uncooled property of the microbolometer, it will have a low cost and be easy for fabrication of large array.

This paper presents a design of 1-THz imaging detectors implemented in 180-nm standard CMOS process. Device simulator is adopted to simulate the performances of the detectors and the results are well consistent with the theoretical predictions. An on-chip patch antenna is designed aided by HFSS. The simulated peak directivity and gain of antenna are 6.9dBi and 4.4dBi, respectively. The -10dB impedance bandwidth of the antenna is 28 GHz, which corresponds to 2.8% relative bandwidth. To improve power transfer efficiency, we extract the input impedance of the MOSFET and design a matching network inserted between the MOSFET and antenna. Imaging pixels have been arranged in a 3 x 5 array in 180-nm standard CMOS process.

A mid-infrared (Mid-IR) spectroscopy system based on optical frequency comb technology is being developed. Using nonlinear optical interactions, the light source in the system generates a tunable optical frequency comb in the Mid-IR wavelength range (λ = 2.5 – 10 μm). The characteristics of this light source (highly coherent, accurately defined frequencies) render the system ideal for use in many applications such as trace gas detections with a long absorption length and high resolution spectroscopy for identification of unknown molecules.

We develop a continuous wave terehertz (THz) imaging system operating at 288 GHz. This imaging system simply consitutes three parts including the source, two optical lenses, and the detector. The entire size is smaller than the tranditional pulsed THz imaging system. In this developed system, the THz wave is generated by a horn attenna which concentrates the wave in an azimuth angle of 3° ~ 5°. The source originates from a singnal generator, and then the frequency increases to 288 GHz after passing through an 8X multiplier. Next, THz wave is focused by a THz lens on the test sample. By controling the sample position in the x-z plane, we can scan it pixel-by-pixel in which each step along the x- or z- axes is 0.1 mm. After penetrating the test sample, another lens collects the transmitted THz wave and focuses them into the thermal detector. This detector can disply the collected THz power. Finally, by drawing the detected power of each pixel, a transmitted-intensity figure for all pixels is obtained. The resolution of this THz imaging system is about 1~2 mm at present. We have measured human molar tooth and obtained its transmitted figures. Besides, we also develop a technology to adjust the positions of the source and detector by a system containing one laser, one beamsplitter, and two mirrors. The relative positions between the source and detector is very important. The input of the source and the output of the detector are small so that they have to aim at each other very accurately in order to collect maximum transmitted power in the detector.

Thermoelectric couple was employed in traditional airplane engine nozzle temperature measurement system with the disadvantages of large size, heavy weight, big error and slow response. This paper presents a new kind of real—time temperature measurement system using laser diode InGaAs/I as light source, and using pyroelectric detector LiTa03 as optical receiving unit and using a microprocessor as signal processing center. This instrument consists of three parts: optical emitting and receiving system, signal amplifying and controlling system, and display system. The principle, structure, anti—interference measure of the system are introduced. Experimental results of airplane engine real—time temperature measurement show that temperature measurement accuracy and response time conform to our requirement in the range of 300°C一800°C and agree with prediction of theory. All these prove that the design is correct.