High-risk liquid chemicals inadvertently enter the surrounding environment during production, storage, transportation, and use, posing a serious threat to ecosystems and human health. How to quickly detect chemical contaminants has become an urgent problem to be solved. In this paper, a new method of short-wave infrared 0.9-1.7 μm hyperspectral imaging telemetry based on liquid crystal tunable filter (LCTF) is proposed to replace the traditional contact non-imaging sampling analysis method. The dichloromethane liquid is characterized and combined with the envelope method and correlation coefficient algorithm for identification imaging. It can achieve remote sensing identification and distribution of four toxic liquids within a short distance of 0.5-1.5 meters, with a spectral resolution of up to 30 nm and a recognition accuracy of 99%. It is a fast and accurate method for detecting surface chemical agents and toxic and hazardous substances on contaminated surfaces. Shorten the time of chemical reconnaissance and improve the efficiency of environmental perception.
Raman lidar is an active remote sensing technology that has been widely applied in fields such as laser atmospheric transmission, global climate prediction, aerosol radiation effects, and atmospheric environment. Raman lidar has the ability to measure target distances and provide spatial depth resolution. It offers high sensitivity and a long detection range without the need for cooperative targets. In this study, a pulsed laser with a wavelength of 355 nm and a single-pulse energy of 350mJ was used as the light source. The spectrometer system employed a blazed grating and a narrowband filter. Signal acquisition was performed using a 450 mm diameter Cassgrain telescope, and a single-photon detector was utilized to enhance the extraction and detection of Raman signals. Outdoor telemetric measurements of dimethyl methylphosphonate (DMMP) gas were conducted. In the vehicle moving mode, target gases could be detected up to a distance of 1.8 km. In the stationary mode, target gases could be detected up to a distance of 5 km.
The fields of safety production, environmental monitoring, public safety, and other areas all benefit greatly from the use of gas detection technologies. The infrared image can represent the spatial distribution of the gas cloud and the background, allowing for long-distance and non-contact detection during hazardous chemical accident rescue. One of the major challenges in gas detection based on infrared imaging is how to choose and gather the spectral information of the gas. It determines the properties of the complete imaging system, including its complexity, the kinds of gases that may be detected, and the sensitivity of the detection. In this paper, a gas detection system based on multispectral infrared imaging was designed, which used short pass and long pass filters to separate light. It was composed of imaging optical system, uncooled focal plane detector, filter wheel and data acquisition and processing system. The rotating filter wheel was used to separate the radiation of the object to obtaining images with different spectral information. Using image processing techniques like image subtraction and spectral angle mapping, the diffusion zone of a gas was estimated. The identified gas cloud was color-mapped in the infrared image. The infrared image had a resolution of 640 × 512, and the time from gas leakage to warning was less than two seconds. The working band of the system was 6.5-14.5 μm, and the real time detection of NH3, SF6, CH4, SO2 was realized.
KEYWORDS: Mirrors, Interferometers, Signal detection, Spectroscopy, FT-IR spectroscopy, Control systems, Michelson interferometers, Infrared spectroscopy, Control systems design, Computer programming
Michelson interferometer is one of the core technologies of time-modulated Fourier transform infrared spectrometer. And the control effect of the interferometer moving mirror has a very important influence on the instrument performance. In this paper, based on the double pendulum interferometer, the control technology of its moving mirror is studied. According to the basic principle of double pendulum interferometer, the general scheme of hardware system design is proposed. And under the guidance of the overall scheme, the modular design of the control system is carried out. There are mainly laser detection modules, main control module, motor drive module, etc. The moving mirror control algorithm is designed in the lower computer software, and the speed of the moving mirror is controlled using the compound control algorithm formed by the combination of incremental PID control and feed-forward control. The control effect of the moving mirror is improved. The upper computer software uses LabVIEW to design and test the control effect of the control system. The test results show that the relative speed error of the moving mirror based on the double pendulum interferometer is better than ±0.35%, and the stability is high, which can meet the requirements of the interference system index.
A radio-frequency (RF) intensity-modulated light source at 532 nm was built for underwater ranging. The intensity of a narrow-linewidth laser at 1064 nm from a NPRO (Non Planar Ring Oscillator) was modulated via a Mach-Zehnder electrooptical modulator. The modulation frequency was tuned from 10 MHz to 2.1 GHz. The intensity-modulated light was amplified via a 2-stage laser diode-pumped Yb3+ doped large-mode-area fiber amplifier. A 15 mm long magnesium oxide doped periodically-poled lithium niobate (MgO: PPLN) nonlinear crystal was used to convert the 1064 nm light into 532 nm light via frequency doubling. The maximum output power at 532 nm was 2.56 W, the highest efficiency from the fundamental to second harmonic generation (SHG) was 22.6%. The watt level 532 nm light source was applied in underwater ranging experiments. Different modulation frequencies were applied to measure the distance of an object in the water. The turbidity of the water was changed by adding Mg(OH)2 powder, ranging accuracy of 6 cm was obtained at 2.5 m distance when the attenuation coefficient of the water was 1.72 m-1. In turbid water, higher modulation frequency was preferable for obtaining higher ranging accuracy.
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