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Development of a near-infrared tunable diode laser absorption spectrometer for trace moisture measurements in helium gas
摘要： There is a demand for water vapor or moisture measurement in gas mixture at trace level from industries like combustion studies, semi-conductor industry, environmental studies, cryogenic services, etc. There are few principles, direct or indirect, to measure moisture—each having individual limitations. Among all, the chilled mirror hygrometer is very accurate but response time is poor; therefore, it is suitable for calibration purposes not for online measurement. An instrument based on near-infrared absorption spectroscopy has been developed and discussed in this article. In this instrument, the laser is modulated with both sinusoidal and slower linear scan, split into two beams: an intense one is passed only through air and the other one through air and the absorption cell of 50 cm length. The balanced detection technique is adopted between the two beams called the reference and the measurement channels, respectively, and the difference signal between the two undergoes the 2-f lock-in detection. This method is good for elimination of moisture present in air and any common-mode noise present in both the channels and as well determines the splitting ratio keeping the absorption cell in vacuum. This method also eliminates the 1-f component present in the signal, which causes asymmetry in the two wings of the 2-f absorption spectra. For computation of absorption spectra, it is found that the Hitran database is sufficient to predict for air as the base gas but Exomol should be used in the cases where helium is the base gas. Simulation and experiment both were performed at different concentration and pressures and the results are found in good agreement for the central spectrum with little difference in wings’ peak. The sensitivity of this instrument achieved at 100 mb pressure in the absorption cell for helium as the base gas with refresh rate of 625 Hz is ～17 ppmv and ～4 ppmv for direct and 2-f measurement, respectively. The applicability of the instrument for air as the base gas is also shown in the paper.
关键词： trace moisture measurements,near-infrared,tunable diode laser absorption spectrometer,helium gas
更新于2025-09-12 10:27:22
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Enhanced terahertz radiation of photoconductive antenna fabricated on GaAs-on-sapphire
摘要： The terahertz (THz) radiation properties of a photoconductive antenna (PCA) fabricated on a GaAs-on-sapphire (GoS) substrate are reported at sub-THz band. The GaAs layer with a thickness of approximately 1 μm was directly deposited on a sapphire wafer by means of molecular beam epitaxy. A butterfly-shaped antenna structure was then fabricated on the GoS substrate by photolithography, and the device was tested as the emitter of an in-house built THz time-domain spectrometer. The performance of this antenna was compared with a commercial one, which had an identical antenna structure but was fabricated on low-temperature-grown GaAs (LT-GaAs). The results showed that the GoS-based PCA radiated an enhanced THz field, which could be as much as 1.9 times that of the LT-GaAs-based PCA, indicating that GoS could be a promising photoconductive material. In addition, the optical transparency of the sapphire substrate allows the device to be illuminated from the backside, which is crucial for THz near-field imaging applications where the sample is usually in close proximity to the front surface of the PCA device.
关键词： photoconductive antenna,molecular beam epitaxy,THz time-domain spectrometer,terahertz,GaAs-on-sapphire
更新于2025-09-12 10:27:22
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Synthesis of ZnO nanoparticles in polyvinyl alcohol solutions using laser assisted synthesis in solution (LASiS) method
摘要： ZnO nanoparticles are widely studied because of their superior properties so they are widely used in various applications. Structural modification with the right synthesis method is the key to getting superior properties. In this experiment, Laser Assisted Synthesis in Solution (LASiS) method was used to synthesize ZnO nanoparticles. The LASIS method was carried out using a metal plate Zn as a target placed in a solution of polyvinyl alcohol (PVA) with different concentrations, namely 1%, 2%, 3% and 4%. This laser ablation has caused a solution of gray colloidal ZnO nanoparticles. Different PVA concentrations do not affect the color of the produced ZnO nanoparticle solution. The properties and structure of ZnO nanoparticles were characterized using UV-Vis spectrophotometer, Zetasizer spectrometer, and Transmission Electron Microscopy (TEM). The UV visible absorbance spectrum shows the maximum absorption characteristics of ZnO nanoparticles observed at a wavelength of 344 nm. The maximum absorbance value rises by increasing the concentration of PVA and reaching the maximum value at a concentration of 3%. These ZnO nanoparticles have a size around 80 nm. TEM analysis shows that ZnO nanoparticles have a spherical shape and have good crystallinity based on SAED measurements. This property is due to the role of PVA in the synthesis process.
关键词： ZnO nanoparticles,polyvinyl alcohol,UV-Vis spectrophotometer,Zetasizer spectrometer,LASiS method,Transmission Electron Microscopy
更新于2025-09-12 10:27:22
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Atomic Force Microscope Guided SERS Spectra Observation for Au@Ag-4MBA@PVP Plasmonic Nanoparticles
摘要： Recently polymer encapsulated surface-enhanced-Raman-scattering (SERS) probes with internal noble metal core–shell structure has found growing applications in biomedical applications. Here we studied the SERS spectra of Au@Ag–4MBA@PVP (4MBA: 4-mercaptobenzoic acid; PVP: polyvinylpyrrolidone) plasmonic nanoparticles produced from a chemical reduction method. By linking the atomic force microscope (AFM) with the homebuilt confocal Raman spectrometer thus to use AFM images as guidance, we realized the measurement of the SERS spectra from separated nanoparticles. We investigated the cases for single nanoparticles and for dimer structures and report several observed results including SERS spectra linearly scaled with laser power, abrupt boosting and abnormal shape changing of SERS spectra for dimer structures. Based on the finite element method simulation, we explained the observed ratio of SERS signals between the dimer structure and the single nanoparticle, and attributed the observed abnormal spectra to the photothermal effect of these plasmonic nanoparticles. Our study provides valuable guidance for choosing appropriate laser power when applying similar SERS probes to image biological cells.
关键词： SERS probes,AFM imaging,confocal Raman spectrometer,SERS spectra,photothermal effect,plasmonic nanoparticles
更新于2025-09-11 14:15:04
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Study on Detecting Dielectric Properties of Typical Electrical Insulation Materials by Terahertz Wave Spectroscopy
摘要： The dielectric properties of the electrical insulation materials is of great importance to the safe operation of the power system. As a promising technique in the field of material testing and with the very adaptive physical modeling of wave transmission process, terahertz wave was used to measure the dielectric properties of five commonly used insulation materials by two methods in this paper. When excluding the echo pulse from the reference signal and the sample signal, a better signal-noise ratio and a wider effective frequency band of spectrums can be obtained. Alternatively, the dielectric properties can also be achieved by separating the main pulse and echo pulse from the sample signal. The latter method makes the sampling of reference signal unnecessary. Furthermore, the dielectric properties of materials were also measured on a relative lower frequency band (1Hz-1MHz) by the broadband dielectric spectrometer. Compared with a relatively lower frequency band, due to the polarization, the dielectric constant of the tested insulation materials was lower on the terahertz band while the dielectric loss tangent was generally higher except the epoxy resin.
关键词： Dielectric properties,Terahertz wave,Insulation materials,Broadband dielectric spectrometer
更新于2025-09-11 14:15:04
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[IEEE 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Paris, France (2019.9.1-2019.9.6)] 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Spectroscopic characterization at THz frequencies of glucose-based biomaterials: paramylon, paramylon-ester and cellulose
摘要： The terahertz (THz) spectroscopy of paramylon (β-1,3-glucan) and paramylon-ester extracted from microalgae called as Euglena have been studied by Fourier Transform Infrared Spectrometer (FT-IR) in a frequency range from 0.3 to 9 THz. The absorption spectra of paramylon were analyzed by comparing them with cellulose that has a similar long-chain -(C6H10O5)n-structure with paramylon. The differences in absorption features between paramylon and cellulose may be caused by their different chain structures. The broad absorption spectra of paramylon-ester can be attributed to some sort of disorder of long-chain molecular vibration modes due to the substitution of propionyl chloride and long-chain acid chloride by esterification.
关键词： microalgae,Euglena,paramylon-ester,paramylon,cellulose,terahertz spectroscopy,Fourier Transform Infrared Spectrometer
更新于2025-09-11 14:15:04
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Photonic Chip-Based Soliton Microcomb Driven by a Compact Ultra-Low-Noise Laser
摘要： Photonics chip-based soliton microcombs have been used in many applications including LIDAR, spectroscopy, coherent communication and astronomical spectrometer calibration [1]. Current-initiated soliton microcombs have been demonstrated [2, 3] recently, signifying improvements in the fabrication of high-Q Si3N4 microresonators. However, both approaches suffer from limited input laser power, thus only demonstrated single-soliton at repetition rates above 149 GHz, which are challenging to detect with commercially available photodetectors. Here we demonstrate a single-soliton generation in 100-GHz-FSR Si3N4 microresonators fabricated using the photonic Damascene reflow process [4], yielding the intrinsic Q-factor exceeding 15 million [5]. Using a compact hybrid laser with narrow linewidth, low relative intensity noise (–160 dBc/Hz at foffset=100 kHz) and high output power up to 100 mW [6], different comb states are observed by simply changing the current of the laser diode, without the need of complex tuning mechanism such as a single sideband modulator [7]. As the laser noise is directly transferred to the soliton comb line, this low-noise laser can be utilized in applications where the phase noise is a critical parameter, e.g. low-noise microwave generation or coherent communication. The experimental setup shown in Fig. 1 (a) consists of an ULN laser operated by a current source and temperature controllers to tune its frequency and power. After the light is coupled into the Si3N4 photonic chip via double inverse nano tapers [8], the temperature of FBG/GC is changed to align the laser wavelength to the resonance of the microresonator. The laser diode current is increased (≈ 330 mA) until soliton existence range is sufficiently long. This is indicated by transmission signal directly observed after the chip on the photodetector (Fig. 1 c). Due to high-Q factor of the Si3N4, the soliton state can be accessed via simply frequency forward tuning [9], without the need of any complex soliton tuning mechanism. Further, different comb states are observed, i.e. modulation instability, multi-soliton state and single-soliton state, via laser diode current tuning. The coherence properties of the soliton-comb teeth is asserted by performing a heterodyne beatnote measurement using a reference laser with a short-time linewidth of 10 kHz (Fig. 1b). The soliton spectrum is fitted with a sech2 function corresponding to a 3 dB bandwidth of ≈19.3 nm and a ≈131.5 fs pulse.
关键词： astronomical spectrometer calibration,Photonics chip-based soliton microcombs,photonic Damascene reflow process,low-noise microwave generation,Si3N4 microresonators,LIDAR,compact hybrid laser,coherent communication,single-soliton generation,spectroscopy
更新于2025-09-11 14:15:04
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Secondary Fluorescence in WDS: The Role of Spectrometer Positioning
摘要： Secondary fluorescence (SF), typically a minor error in routine electron probe microanalysis (EPMA), may not be negligible when performing high precision trace element analyses in multiphase samples. Other factors, notably wavelength dispersive spectrometer defocusing, may introduce analytical artifacts. To explore these issues, we measured EPMA transects across two material couples chosen for their high fluorescence yield. We measured transects away from the fluorescent phase, and at various orientations with respect to the spectrometer focal line. Compared to calculations using both the Monte Carlo simulation code PENEPMA and the semi-analytical model FANAL, both codes estimate the magnitude of SF, but accurate correction requires knowledge of the position of the spectrometer with respect to the couple interface. Positioned over the fluorescent phase or otherwise results in a factor of 1.2–1.8 of apparent change in SF yield. SF and spectrometer defocusing may introduce systematic errors into trace element analyses, both may be adequately accounted for by modeling. Of the two, however, SF is the dominant error, resulting in 0.1 wt% Zn apparently present in Al at 100 μm away from the Zn boundary in an Al/Zn couple. Of this, around 200 ppm Zn can be attributed to spectrometer defocusing.
关键词： defocusing,secondary fluorescence,spectrometer positioning,wavelength dispersive spectrometer,electron microprobe
更新于2025-09-10 09:29:36
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[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia, Spain (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - UAV-BASED INTEGRATED MULTISENSOR PAYLOAD FOR HIGH RESOLUTION IMAGING
摘要： This paper describes the development of a multisensor UAV-based imaging platform. A sensor package consisting of a LiDAR, imaging spectrometer, and RGB camera were integrated with an inertial navigation system. This package is currently being flown on a hexacopter. A number of data acquisition missions have been conducted with this platform, including the imaging of a small active rotational mass movement, a wetland estuary, and several vineyards.
关键词： SfM point cloud,UAV,imaging spectrometer,LiDAR,INS
更新于2025-09-10 09:29:36
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High Resolution Binary Zone Plate in Double-Sided Configuration for Terahertz Radiation Focusing
摘要： A double-sided phase-reversal binary zone plate is numerically investigated and experimentally characterized at the frequency of 1 THz. The double-sided zone plate has a novel design based on a binary phase-reversal zone plate, in which the total zone thickness is split in two halves located at a distance optimized by means of numerical simulations. The samples are fabricated by a three-axis milling technique on slabs of an ultralow-loss cyclo-olefin polymer. The lenses’ characterization at the frequency of 1 THz is performed by means of a THz time-domain spectrometer, in terms of both focal length and spatial resolution. The focusing properties of the double-sided zone plate are compared with those of a conventional binary zone plate. The double-sided zone plate features 2.4 times smaller focal spot, 1.25 times higher focusing efficiency, and an approximately 10λ0 longer depth of field than the conventional binary configuration.
关键词： knife-edge technique,time-domain spectrometer,terahertz radiation,Diffractive lenses
更新于2025-09-10 09:29:36