The dependence of the ratio between the second and first harmonic signals in wavelength-modulation spectroscopy is calculated for the precise absorption measurement that is applied to gas sensing. In the calculation, the amplitude modulation of the laser is considered as well as the frequency modulation. First, the dependence of signals on peak optical depth is discussed for the Lorentzian and Gaussian lines. Next, the dependence of signals on gas concentration is calculated in a weak absorption-limit. Finally, a numerical example is explained taking into consideration both peak optical depth and gas concentration. 相似文献
Monitoring the aquatic environment and the life of free‐floating organisms remains on the borderline of our technical capabilities. Therefore, our insights into aquatic habitats, such as, abundance and behavior of organisms are limited. In order to improve our understanding of aquatic life, we have developed a low‐cost inelastic hyperspectral lidar with unlimited focal depth and enough sensitivity and spatiotemporal resolution to detect and resolve position and behavior of individual submillimeter organisms. In this work, we demonstrate elastic as well as molecular ranging by using the water Raman band, and by observing fluorescence from chlorophyll and from dye‐tagged organisms. We present an aquatic laser‐diode‐based inelastic light detection and ranging (lidar) system with unprecedented sensitivity, spatiotemporal resolution and number of spectral bands. Our system offers new opportunities for quantitative in situ studies of aquatic organisms, and has the potential to considerably advance our understanding of biological life in aquatic systems.
We are building a long-range FM/cw nonscanning imaging lidar breadboard. This lidar system achieves ranging based on a frequency
modulation/continuous wave (FM/cw) technique, implemented by an amplitude modulated mid-IR diode laser transmitter with a
linear frequency modulation (LFM) of the subcarrier. Firstly, various schemes of light beam modulation are analyzed. Secondly,
we put forward a laser modulation scheme whose core was formed by a 1.55 μm electro-absorption modulated laser diode (EML) and an erbium-doped optical fiber amplifier (EDFA), then a corresponding
experimental system architecture and components for light beam modulation and detection are established. Finally, a corresponding
experiment of laser beam modulation is completed for the first time. In our experiment, the EML amplitude is modulated by
a 200 MHz to 800 MHz LFM signal, whose amplitude value is 2.05 V. The average output power of the modulated laser obtained
in the experiment is 10 W, peak power is 16.4 W, and the average modulation depth is 78%. The results of tests predict that
this laser modulation scheme is likely to improve the imaging range of the FM/cw lidar. 相似文献
The economic loss and the threat to personal safety caused by the leakage of hazardous chemical gases in natural gas stations, mining, industrial chemicals, manufacturing, gas pipeline transportation and other places are huge. It is extremely necessary to strengthen the real-time monitoring and warning of such hazardous chemical gas leaks. However, traditional detection methods have defects such as slow response, high maintenance cost, low efficiency, the need for close contact sampling and testing, and the inability to monitor in real time. In recent years, tunable diode laser absorption spectroscopy has become a key technology for trace gas detection, with the advantages of fast measurement response and strong wavelength selectivity. In order to realize real-time, long-distance and non-contact monitoring of hazardous chemical gas leakage and to improve monitoring efficiency and accuracy, a multi-component trace gas remote sensing system based on wavelength modulation spectroscopy is proposed. The core of the system is based on STM32 chip combined with a self-designed driver circuit to control the laser, and the second harmonic signals of methane, ammonia and acetylene are extracted separately by using different modulation frequencies to realize simultaneous, real-time and long-distance detection for the mixed gases. We use wavelength modulated spectroscopy with light intensity modulation amplitude normalization to make the remote sensing results free from the influence of the echo laser on the signal intensity. By comparing the direct absorption signal and the second harmonic signal of the gas concentration detected by the system, it is verified that the wavelength modulation technique has a significant noise suppression effect and can greatly improve the detection sensitivity and detection distance. Through calibration experiments, the measurement accuracy and lower detection limits of the system are evaluated. The experiments have shown that the lower detection limits of the system can reach 87 ppm·m, 212 ppm·m and 12 ppm·m for methane, ammonia and acetylene, respectively, and the measurement error is less than 10%. We tested the remote detection performance of the system over long distances, and the results showed that the remote detection distance can be up to 40 m. The system provides a multi-component, real-time, synchronous, high-sensitivity, long-distance and stable performance remote sensing solution for the research and application of laser trace gas detection, which can be widely used in gas monitoring and early warning of mine disasters, gas leakage monitoring and early warning of hazardous chemical field stations and transportation pipeline networks. 相似文献
ABSTRACT We analyze the influence of random errors and absorption shape fitting errors on gas concentration measurement in tunable diode laser absorption spectroscopy. We then propose a new data processing method according to the characteristic of random errors and fitting absorption shape. This method only uses the integral value within the half width at half maximum of the fitting absorption shape to determine the gas concentration in actual measurements. Meanwhile, the O2 transition at 13,150.197 cm?1 is selected to measure the O2 concentration using this method. Compared with the traditional method, the method established in this paper can accurately measure O2 concentration. 相似文献
Error determination is a critical issue in differential absorption lidar (DIAL). In this paper, some common error calculations are compared by applying them to a set of artificial data. First, three methods for the evaluation of the signal-to-noise ratio (SNR) of the lidar return have been examined. Then, the effect of the application to DIAL measurements of correction algorithms is investigated. The mean value and the standard deviation of the set of artificial data have been obtained from experimental determinations accomplished with our system. This was made possible by the shot-per-shot recording of the lidar return. The results of this study allows us to recommend a new method for the data analysis used in DIAL experiments: the SNR should be directly measured and all sources of statistical fluctuation have to be taken into account in the calculation of the final error. Otherwise such error could be underestimated, as suggested also by the disagreement of simultaneous measurements carried out by different systems. 相似文献
