This PDF file contains the front matter associated with SPIE Proceedings Volume 8366, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

There is an increasing need for rapid and accurate detection, identification, and quantification of chemical, biological, and energetic hazards in many fields of interest. To meet these challenges, researchers are combining spectroscopy with nanoscale platforms to create technologies that offer viable and novel solutions for today's sensing needs. One technology that has gained increasing popularity to meet these needs is surface enhanced Raman scattering (SERS). For ideal SERS sensing, commercially available uniform and reproducible nanoscale surface demonstrating high sensitivity are desirable. If these surfaces can be modified for the selective sensing of hazard materials, an ideal sensor platform for dynamic in field measurements can be imagined. In this proceedings paper, preliminary efforts towards the characterization and application of commercially available next generation Klarite substrates will be demonstrated and efforts towards selective sensing will be discussed.

Raman spectroscopy is a well established analytical method with applications in many areas, e.g. analysis of biological samples. To overcome the problem of an undesired fluorescence background masking the Raman signals we present a multi-spectral approach using shifted excitation Raman difference spectroscopy (SERDS). For our investigations we applied microsystem diode lasers which realize two slightly shifted excitation wavelengths required to perform SERDS at 488 nm, 671 nm, and 785 nm. The emission at 488 nm with an optical power of up to 30 mW and a spectral shift of 0.3 nm (12 cm^-1) is realized by frequency doubling of a 976 nm distributed feedback (DFB) diode laser. The 671 nm laser diode contains two separate laser cavities (spectral shift: 0.7 nm (13 cm^-1)) each incorporating a volume Bragg grating as frequency selective element. In that case, optical powers up to 50 mW can be obtained. For investigations at 785 nm we used a DFB laser with a maximum optical power of 110 mW and a spectral shift of 0.5 nm (7 cm^-1). Meat, fat tissue, connective tissue and bones from pork and beef were used as test samples to demonstrate the effective background removal using SERDS. For all three wavelengths integration times of only 5 - 10 seconds were necessary showing the possibility of SERDS for rapid sample identification. A comparison with conventional Raman spectra is given pointing out the improvement of spectral quality. The applicability of SERDS for other analytical applications, e.g. medical diagnosis will be discussed.

Conducting polymers are potentially useful materials in sensor applications. Polyaniline is one of the most promising of these materials due to high conductivity and plasma frequencies as high as the mid-infrared. The application of this material is still limited because of low conductivity. In this paper, we chemically prepared a composite of co-doped polyaniline with hydrochloric acid and MSA (methane sulfonic acid) in aqueous solution with both colloidal and nano-graphite. Solutions of the composite material were prepared in m-cresol and NMP (N-mthyle-2-pyrrolidone), which are common organic solvents. This approach resulted in material with conductivity higher than either intrinsic polyaniline or graphite alone. The solution of the composite was spin coated on suitable substrates. The thicknesses of the films were measured using atomic force microscope (AFM). Fourier transform infrared spectra (FTIR) and micro-Raman spectra were collected to confirm the composition and determine the infrared thickness. Surface plasmon resonances for grating patterns of this composite material were calculated using experimental determined infrared (IR) ellipsometry data. The goal is to identify a material which has potential application for surface plasmons resonance sensing with high sensitivity and selectivity in IR range.

We demonstrate the potential use of silver nanorod (AgNR) array substrates for on-chip separation and detection of chemical mixtures by ultra-thin layer chromatography (UTLC) and surface enhanced Raman spectroscopy (SERS). The capability of the AgNR substrates to separate different compounds in a mixture was explored using a mixture of the food colorant Brilliant Blue FCF and lactic acid, and the mixtures of Methylene Violet and BSA at various concentrations. After the UTLC process, spatially-resolved SERS spectra were collected along the mobile phase development direction and the intensities of specific SERS peaks from each component were used to generate chromatograms. The AgNR substrates demonstrate the capability of separating Brilliant Blue from lactic acid, as well as revealing the SERS signal of Methylene Violet from the massive BSA background after a simple UTLC step. This technique may have significant practical implications in actual detection of small molecules from complex food or clinical backgrounds.

Naphthalene has been identified by the National Research Council as a serious health hazard for personnel working with jet fuels and oil-based sealants containing naphthalene. We are developing a family of miniature, self-contained, direct reading personal exposure monitors (PEMs) to detect, differentiate, quantify, and log naphthalene and other volatile organic compounds (VOCs) in the breathing zone of the wearer or in the hands of an industrial hygienist with limits of detection in the low parts per billion (ppb) range. The VOC Dosimeter (VOCDos) described here is a PEM that provides real-time detection and data logging of exposure as well as accumulated dose, with alarms addressing long term and immediate exposure limits. We will describe the sensor, which employs optical methods with a unique excitation source and rapidly refreshable vapor concentrator. This paper addresses the rapidly increasing awareness of the health risks of inhaling jet fuel vapors by Department of Defense (DOD) personnel engaged in or around jet fueling operations. Naphthalene is a one to three percent component of the 5 billion gallons of jet fuels used annually by DOD. Naphthalene is also a component of many other petroleum products such as asphalt and other oil-based sealants. The DOD is the single largest user of petroleum fuels in the United States (20% of all petroleum fuel used). The VOCDos wearable sensor provides real-time detection and data logging of exposure as well as accumulated dose. We will describe the sensor, which employs endogenous fluorescence from VOCs accumulated on a unique, rapidly refreshable, patent-pending concentrator, excited by a unique deep ultraviolet excitation source.

Detection and identification of gas species using tunable laser diode laser absorption spectroscopy has been performed using vertical cavity surface emitting lasers (VCSEL). Two detection methods are compared: direct absorbance and wavelength modulation spectroscopy (WMS). In the first, the output of a DC-based laser is directly monitored to detect for any quench at the targeted specie wavelength. In the latter, the emission wavelength of the laser is modulated by applying a sinusoidal component on the drive current of frequency ω, and measuring the harmonics component (2ω) of the photo-detected current. This method shows a better sensitivity measured as signal to noise ratio, and is less susceptible to interference effects such as scattering or fouling. Gas detection was initially performed at room temperature and atmospheric conditions using VCSELs of emission wavelength 763 nm for oxygen and 1392 nm for water, scanning over a range of approximately 10 nm, sufficient to cover 5-10 gas specific absorption lines that enable identification and quantization of gas composition. The amplitude and frequency modulation parameters were optimized for each detected gas species, by performing two dimensional sweeps for both tuning current and either amplitude or frequency, respectively. We found that the highest detected signal is observed for a wavelength modulation amplitude equal to the width of the gas absorbance lines, in good agreement with theoretical calculations, and for modulation frequencies below the time response of the lasers (<50KHz). In conclusion, we will discuss limit of detection studies and further implementation and packaging of VCSELs in diode arrays for continuous and simultaneous monitoring of multiple species in gaseous mixtures.

US EPA's Clean Air Act lists 187 hazardous air pollutants (HAP) or airborne toxics that are considered especially harmful to health, and hence the measurement of their concentration is of great importance. Numerous sensor systems have been reported for measuring these toxic gases and vapors. However, most of these sensors are specific to a single gas or able to measure only a few of them. Thus a sensor capable of measuring many of the toxic gases simultaneously is desirable. Laser photoacoustic spectroscopy (LPAS) sensors have the potential for true broadband measurement when used in conjunction with one or more widely tunable laser sources. An LPAS gas analyzer equipped with a continuous wave, room temperature IR Quantum Cascade Laser tunable over the wavelength range of 9.4 μm to 9.7 μm was used for continuous real-time measurements of multiple gases/chemical components. An external cavity grating tuner was used to generate several (75) narrow line output wavelengths to conduct photoacoustic absorption measurements of gas mixtures. We have measured various HAPs such as Benzene, Formaldehyde, and Acetaldehyde in the presence of atmospheric interferents water vapor, and carbon dioxide. Using the preliminary spectral pattern recognition algorithm, we have shown our ability to measure all these chemical compounds simultaneously in under 3 minutes. Sensitivity levels of a few part-per-billion (ppb) were achieved with several of the measured compounds with the preliminary laboratory system.

MR-i is an imaging version of the ABB MR series Fourier-Transform spectroradiometer. This field instrument generates spectral datacubes in the MWIR and LWIR. It is designed to acquire the spectral signatures of rapidly evolving events. The MR-i is modular and can be configured in different ways. One of its configurations is optimized for passive standoff measurements of gases in differential mode. In this mode, the instrument is equipped with a dual-input telescope to perform optical background subtraction. The resulting signal is the differential between the spectral radiance entering each input port. With that method, the signal from the background is automatically removed from the signal of the target of interest. The spectral range of this configuration extends in the VLWIR (cut-off near 14 μm) to take full advantage of the LW atmospheric window.

Investigations on the seafloor in the arctic area are of great scientific interest as well as of progressive economic importance. Therefore, measurements in the water column and of sediments were carried out by applying different analytical methods. In JCR 253 arctic cruise a microsystem diode laser with reflection Bragg grating emitting at 671 nm was introduced and integrated into an optode housing which was laboratory pressure tested up to 200 bar. The connection to the mobile spectrometer is realized through an optical fiber. All performed measurements were carried out on the James-Clark-Ross research vessel during a three week experiment in August 2011. Conventional Raman spectra and SERS spectra of arctic surface water and sediment acquired from locations around 78° N and 9° E will be presented. Selected SERS substrates developed for SERS measurements in sea-water were tested for their capability to detect different substances in the water down to very small (pmol/l) concentrations. Additionally, the applicability of shifted excitation Raman difference spectroscopy (SERDS) and a combination of SERS with SERDS for analytical applications during sea-trials for in-situ analyses of sea-water and sediments will be discussed.

The maintenance and repair of reinforced concrete structures, especially those submerged in the sea-water, require effective inspection and monitoring techniques for assessing the state of corrosion in reinforcement material. An underwater inspection system was developed which is able to monitor the reinforcement corrosion. The system is ROV equipped with the sealed tube neutron generator (NG). By rotating the NG and by using the associated alpha particle technique it is possible to measure the concrete cover depth together with the reinforcing bar diameter. The possibility to estimate the carbon and chloride content in the concrete was investigated. Iron plates of different thickness, covered by 6 cm thick concrete block, were successfully detected and the thickness of the concrete cover was estimated. In addition, reinforced bar of one and three centimeters in diameter was identified and measured.

To investigate the optimal gold colloid film properties for the in-situ detection of polycyclic aromatic hydrocarbon (PAH) in water using 671 nm excitation wavelength, gold substrates with selected sizes of gold nanoparticles were prepared. Heating of (3-aminopropyl)trimethoxysilane (APTMS) methanol solution allowed to control the surface plasmon resonance for surface enhanced Raman spectroscopy (SERS). Shifted excitation Raman difference spectroscopy (SERDS) was applied for effective background removal. Results for pyrene in aqueous solution demonstrate that there is a dependence of SERS activity on the size of gold nanoparticles even though their surface plasmon resonances are almost same and close to the excitation wavelengths, and also confirmed that the improved self-assembly method using controlling the temperature of APTMS solution way can work well. Appling the substrate with the average gold nanoparticles size of 35 nm, different concentrations of pyrene in aqueous solution were detected with SERS supported by SERDS technique. Raman signals of pyrene up to 5 nmol/l on this substrate can be obtained. The quantitative analysis shows the SERS intensities increase with the increasing concentration of pyrene, which is the foundation of quantitative analysis of pyrene in aqueous solution.

A solar-powered, battery-operated, atmospheric-pressure, self-igniting microplasma the size of a sugar-cube developed on a hybrid, 3d-chip is described. Rapid prototyping of the 3d-chip; some fundamental aspects and a brief characterization of its background spectral emission using a portable, fiber-optic spectrometer are discussed.

The detection of pollutant chemicals in water, from waste water up to drinking water, is of worldwide interest. Fast response chemical sensors based on Raman spectroscopy are well suited for a rapid identification and quantification of such substances. Because of the weak Raman scattering intensity surface-enhanced Raman scattering (SERS) was applied to achieve the high sensitivity necessary for trace detection. In the European Commission project SENSEnet, a SERS sensor based on a naturally grown Ag nanoparticle ensemble was developed and adapted for in-situ detection of polycyclic aromatic hydrocarbons (PAHs) in water. Silver nanoparticle ensembles with surface plasmon resonance (SPR) wavelengths around 488 nm were prepared under ultrahigh vacuum condition by Volmer-Weber growth on quartz plates. The laboratory set-up for Raman spectroscopy contains a microsystem frequency-doubled diode-laser which generates two emission wavelengths, 487.61 nm and 487.91 nm, thus the system was configured also for shifted excitation Raman difference spectroscopy (SERDS). The optical output power is up to 20 mW. The SERS substrate is located inside a flow-through cell which provides continuous flow conditions of an analyte solution. The SERS spectra were recorded using a laboratory spectrograph with a back-illuminated deep depletion CCD-detector. We present an atomic force microscopic image of the developed SERS substrates as well as results for the SERS activity and the limit of detection of selected PAHs, e.g. pyrene, in water with respect to the SPR wavelength. SERS/SERDS measurement of water samples containing mixture of several PAHs (e.g. pyrene and fluoranthene) down to the detection limit of 2 nmol/l will be discussed.

The US Congress has passed legislation dictating that all government agencies establish a plan and process for improving energy efficiencies at their sites. In response to this legislation, Oak Ridge National Laboratory (ORNL) has recently conducted a pilot study to explore the deployment of a wireless sensor system for a real-time measurement-based energy efficiency optimization framework within the steam distribution system within the ORNL campus. We make assessments on the real-time status of the distribution system by observing the state measurements of acoustic sensors mounted on the steam pipes/traps/valves. In this paper, we describe a spectral-based energy signature scheme that interprets acoustic vibration sensor data to estimate steam flow rates and assess steam traps health status. Experimental results show that the energy signature scheme has the potential to identify different steam trap health status and it has sufficient sensitivity to estimate steam flow rate. Moreover, results indicate a nearly quadratic relationship over the test region between the overall energy signature factor and flow rate in the pipe. The analysis based on estimated steam flow and steam trap status helps generate alerts that enable operators and maintenance personnel to take remedial action. The goal is to achieve significant energy-saving in steam lines by monitoring and acting on leaking steam pipes/traps/valves.

An efficient large-scale recycling approach of particulate solid wastes is always accomplished according to the quality of the materials fed to the recycling plant and/or to any possible continuous and reliable control of the different streams inside the processing plants. Processing technologies addressed to recover plastics need to be extremely powerful, since they must be relatively simple to be cost-effective, but also accurate enough to create high-purity products and able to valorize a substantial fraction of the plastic waste materials into useful products of consistent quality in order to be economical. On the other hand, the potential market for such technologies is large and the boost of environmental regulations, and the oil price increase, has made many industries interested both in "general purpose" waste sorting technologies, as well as in developing more specialized sensing devices and/or inspection logics for a better quality assessment of plastic products. In this perspective recycling strategies have to be developed taking into account some specific aspects as i) mixtures complexity: the valuable material has to be extracted from the residue, ii) overall production: the profitability of plastic can be achieved only with mass production and iii) costs: low-cost sorting processes are required. In this paper new analytical strategies, based on hyperspectral imaging in the near infrared field (1000-1700 nm), have been investigated and set up in order to define sorting and/or quality control logics that could be profitably applied, at industrial plant level, for polyolefins recycling.

The synthesis, spectroscopic characterization and complexing properties of calixarene-based fluorescent sensors are reported. The calixarene bearing four dansyl fluorophores (Calix-DANS4) exhibits a very high affinity for the detection of lead. A fluorimetric micro-device based on the use of a Y-shape microchannel was developed and allows lead detection with a 5 ppb detection limit. For mercury detection, a fluorescent molecular sensor containing a calixarene anchored with four 8-quinolinoloxy groups (Calix-Q) has been synthesized. The absorption and fluorescence spectra of this sensor are sensitive to the presence of metal cations. An efficient fluorescence quenching is observed upon mercury complexation because of a photoinduced electron transfer from the fluorophore to the bound mercury. Calix-Q shows a high selectivity towards Hg²⁺ over interfering cations (Na⁺, K⁺, Ca²⁺, Cu²⁺, Zn²⁺, Cd²⁺ and Pb²⁺) and a 70 ppb sensitivity.

The research presented in this paper improves potential for the application of surface-enhanced Raman scattering (SERS) in remote detection and analysis. Remote (stand-off) Raman sensing, with its ability to "fingerprint" analyte based on their unique vibrational spectra, offers great potential to address the challenging analytical problem of identifying unknown substances in low concentrations in the form of vaporous emissions or clouds. An inexpensive nebulizer/spray chamber was designed to study the mixing of aerosolized SERS (surface-enhanced Raman scattering) active nanostructures with a vapor phase analyte, the fluorophore Rhodamine 6G (R6G). Improved signal intensities (EF=200) are gained via SERS. Vapor phase mixing of the analyte and substrate is rapid (< 5 seconds).

CELiS (Compact Eyesafe Lidar System) is a tactical elastic lidar system commissioned by the Strategic Environmental Research and Development Program (SERDP) for the purpose of air quality environmental compliance issues surrounding the offroad use of wheeled and tracked vehicles. A complete CELiS instrument weighs less than 300 lbs., is less than 2 cubic meters in volume and uses 700 W of 120V AC power. CELiS has a working range of better than 2km and a range resolution of 5m.

We investigate our recently demonstrated remote air laser by studying the directional backwards and forward emission at 845nm while monitoring the atomic oxygen excitation using a microwave scattering technique. We study the high gain achieved by focusing an UV laser in air in order to produce and excite the oxygen atoms responsible for the stimulated emission, which is strongly dependent on the optical parameters of the pump. The standoff air laser can be used as a remote detector for molecular and atomic species which affect the optical propagation of the pump laser either directly or via optical stimulation.

This paper explores the performance of current remote sensing methods for estimation of fine particulate matter (PM_2.5, diameter < 2.5μm) in the New York City area (40.821°N, 73.949°W) during 2010. We analyze the relationship between surface PM2.5 mass concentration and column aerosol optical depth (AOD) at 500-nm by using the synergy measurements of surface in-situ, AERONET-sunphotometer, lidar and NOAA-GOES satellite. The regression slopes and correlation coefficients between PM_2.5 and AOD show the good performance in summer and indicate dramatic monthly variation which are associated with the seasonal differences of PBL-heights, fine-mode contribution to the total AOD and aerosol volume-to-extinction ratio. Additionally, the relationship of PM_2.5 and fine-mode AOD shows higher correlations than the PM_2.5 and total AOD (R² _total = 0.5011, R² _fine = 0.6132, R² _coarse = -0.0235). Also, when considering the lidar-derived PBL-heights in the different months and removing aloft layer and cloudy cases, the PM_2.5 estimations using AOD show improvements during the cold months; furthermore, the correction on aerosol volume-to-extinction ratio results in better estimations of fine particulate matter concentrations and therefore confirms the importance of including these parameters into air quality models. Moreover, the AOD data from NOAA-Geostationary Operational Environmental Satellites (GOES) are initially evaluated by comparing with AERONET-AOD, and further illustrate the good correlation with PM_2.5 concentration.

Water vapor is the most important atmospheric greenhouse gas, but its variability and distribution, particularly the vertical profile, are not well known due to a lack of reliable long-term observations in the upper troposphere and stratosphere. Additional design and testing is necessary to extend Water Vapor Sensor System (WVSS) sensitivity to water vapor from a threshold of 100 ppmv to 2.8 ppmv to support operational and climate applications. Laser photoacoustic spectroscopy (LPAS) technique can extend the sensitivity to this level without extending absorption chamber path or using expensive laser emitting at stronger absorption line. A laser photoacoustic spectroscopy sensor based on inexpensive telecommunication style packaged, fiber-coupled near IR distributed feedback (DFB) laser diodes was developed to quantify concentrations of water vapor (H2O), CO2, and methane in ambient air. The LPAS sensor assembled in a compact package was designed for airborne, real-time measurements of atmospheric components. A resonant photoacoustic cell is used to increase the photoacoustic signal, electrical modulation is applied to replace mechanical chopper, and wavelength modulation spectroscopy is used to minimize the interfering background signal from window absorption in the sample cell. The minimum detection sensitivities (1σ) of 5 ppm at 1.39 μm (5 mW) for water vapor, 6 ppm at 1.6 μm (15 mW) for CO₂, and 3 ppm at 1.6 μm (15 mW) for methane, are reported.

The employment of nanowires is a very powerful strategy to improve gas sensor performance. We demonstrate a gas sensor device, which is based on silicon chip-to-chip synthesis of ultralong tin oxide (SnO₂) nanowires. The sensor device employs an interconnected SnO₂ nanowire network configuration, which exhibits a huge surface-to-volume ratio and provides full access of the target gas to the nanowires. The chip-to-chip SnO₂ nanowire device is able to detect a H₂ concentration of only 20 ppm in synthetic air with ~ 60% relative humidity at room temperature. At an operating temperature of 300°C a concentration of 50 ppm H₂ results in a sensitivity of 5%. At this elevated temperature the sensor shows a linear response in a concentration range between 10 ppm and 100 ppm H₂. The SnO₂-nanowire fabrication procedure based on spray pyrolysis and subsequent annealing is performed at atmospheric pressure, requires no vacuum and allows upscale of the substrate to a wafer size. 3D-integration with CMOS chips is proposed as viable way for practical realization of smart nanowire based gas sensor devices for the consumer market.

Pumps are widely used in chemical analysis. For instance, they are used to help transport liquid samples from a beaker to an instrument, for example for sample introduction. Pumps can also used to evacuate chambers used for mass spectrometry. For miniaturized, portable analytical instruments, miniaturized pumps are ideally suited. In this paper, a micropump with no moving parts that relies on the Venturi effect has been rapidly prototyped by imprinting fluidic channels on inexpensive polymeric substrates. The micropump was first evaluated for potential vacuum applications (e.g., for portable mass spectrometers). Subsequently, it was evaluated for its ability to transfer liquids in microfluidic channels (for possible use as a sample delivery vehicle to an appropriate sample introduction system).

We present the detection of volatile organic compounds directly in their vapor phase by surface-enhanced Raman scattering (SERS) substrates based on lithographically-defined two-dimensional rectangular array of nanopillars. The type of nanopillars is known as the tapered pillars. For the tapered pillars, SERS enhancement arises from the nanofocusing effect due to the sharp tip on top. SERS experiments were carried out on these substrates using various concentrations of toluene vapor. The results show that SERS signal from a toluene vapor is strongly influenced by the substrate temperature, and the toluene vapor can be detected within minutes of exposing the SERS substrate to the vapor. A simple adsorption model is developed which gives results matching the experimental data. The results also show promising potential for the use of these substrates in environmental monitoring of gases and vapors.

We present the use and characterization of a Single Photon Avalanche Detector (SPAD) for shot-noise-limited imaging at ultra-low light-level. Many demanding photonic applications, such as fluorescence laser scanning microscopy, require the acquisition of very weak optical signals, generally composed by few photons mostly in the visible and near infrared wavelength. Conventional photo detector that utilizes analog current integration is generally not able to detect such low intensity signal due to the excessive noise at low signal levels. In this paper, we demonstrate shot-noise-limited imaging by scanning and using N-photon photo-detection implemented with a Single Photon Avalanche Detector. We choose a LabView based approach, extending the methods of N-photon photo-detection. In our implement, the number of TTL pulses received from the Single Photon Avalanche Detector within the duration of the pixel dwell time is recorder by a LabView pre-programmed instrument and then wrote into a pre-allocated image array, using the pixel clock and line sync signals to determine the position within the image. Experiments show that our N-photon photo-detection exhibits extreme sensitivity even down to single photon level. This characteristic of the ultra-sensitivity makes this scheme very suitable for low signal levels in fluorescence laser scanning microscopy. Related with the dynamic range, the maximum count rate of our N-photon photo-detection scheme reaches 106 counts per second (cps) while maintaining high detection efficiency. It has also been demonstrated that the thermoelectrically cooled Single Photon Avalanche Detector neutralizes dark counting noise of detector and thus obtain a nearly shot-noise-limited imaging performance.

Terahertz time domain spectroscopy (THz-TDS) is a new kind of nondestructive detection method, frequency of terahertz wave spans from a few tens of GHz to several THz, which is used to detect material because of its strong identification, it can supply rich vibration information caused by intermolecular and large intra-molecular. Ammonium sulfamate (AMS) is a kind of herbicide, it has special value for many woody plants, which can prevent annual weeds. The excess use of pesticide is a huge threaten for human health in recent years, thus the research on detection of pesticide has absolutely important meaning, in this paper, pure AMS and mixture samples of AMS and orange are measured using THz-TDS, and their absorption coefficient are calculated by the model, which is put forward based on Fresnel equation. We qualitatively analyze the absorption coefficient spectra of pure AMS, which is useful for us to identify the pesticide in agriculture products. Meanwhile, we measured 14 mixture samples of AMS and orange, the weight ratio of mixtures are from 0% to 59.9%. Nine samples are considered as calibration set and the other five samples are regarded as prediction set, to quantitatively analyze the concentration of AMS by the partial least squares (PLS), the result shows that the prediction error is less then 4.5%, in addition, the relationship of the average absorption and weight ratio are absolutely linear. The experiment demonstrates that THz-TDS is promising and efficient to quantitatively detect the component of mixtures, and it has important reference value for the detection of pesticide in agriculture food.

Open path IR gas detectors are a mainstay in the oil and gas industry. They are used in a variety of instances to identify gas accumulations or monitor gas cloud migrations. In offshore installations, open path optical gas detectors are used to monitor drilling and production operations, crude oil separation, compression, and exhaust and ventilation systems. Because they can monitor a perimeter or fence line, they are ideally suited for detecting gas in open facilities, where point gas detectors would be difficult or expensive to deploy. Despite their widespread use, open path optical gas detectors are rarely employed to detect low level concentrations of combustible gases. Standard models are typically set to alarm at 50% LEL-m (50% LEL extended over one meter), providing sufficiently early warning when gas accumulations occur. Nevertheless, in cases in which a combustible gas is diluted quickly, such as ventilation exhaust ducting, it may be necessary to set the detector to alarm at the lowest predictable level. Further, interest in low level infrared gas detection has been growing as gases such as CH₄ and CO₂ are greenhouse gases. The present paper describes a mid-wave infrared (MWIR) open path system designed to detect combustible and carbon dioxide gas leaks in the parts-per-million-meter (ppm-m or mg/cm²). The detector has been installed in offshore platforms and large onshore facilities to detect a variety of flammable gases and vapors. Advantages and limitations of the system are presented. False alarm immunity and resilience to atmospheric interferences are also discussed.