The Fabry-Parot etalon can be widely used in the lidar for Doppler wind measurement and aerosol detection. Due to the very wide application of the FP etalon, the standard transmission curve of the F-P is a very important parameter. The general FP etalon measures the transmittance curve by tuning the wavelength of the laser source or tuning the angle of incident light. The FP etalon generally measures the transmittance curve of the etalon by tuning the wavelength of the laser source or use the frequency comb source. Moreover, the tuning of the wavelength and the angle of incident light are nonlinear, and the measurement accuracy is insufficient, and the frequency comb source is very expensive. This paper proposes a new method for testing the transmittance curve of a FP etalon using a similar frequency comb source. The whispering gallery mode is a typical similar frequency comb laser source which has multiple frequency components, but not equal intervals. The spacing of the frequency of the whispering gallery mode is not equal, but the spacing of the frequency can be determined. So, the transmittance curve of the FP etalon can be measured at one time. And the frequency interval and spectral range are tunable easily. This new method greatly reduces the cost of measuring transmission curve, improve measurement accuracy and effectiveness and has great theoretical and practical value.
As the increasing demands of the environmental protection, meteorological monitoring, ecological detection and other fields, lidars are needed to simultaneously measure a variety of atmospheric parameters (especially simultaneous measurement of various pollutants, such as volatile organic solvent VOCs). Multi-wavelength Raman lidar, differential absorption lidar (DIAL) and high spectrum resolution lidar (HSRL) can be implemented these fields. But either technique needs multiple laser sources to meet their requirements. This paper proposes a new lidar based on Frequency Comb Light Source, which can provide multiple frequency components through a single light source for simultaneously measuring various multiple atmospheric parameters. The frequency comb laser light source is used to emit seed light of frequency ωc from the seed laser, and then after passing through the frequency comb laser, a series of equally spaced spectral frequency components are emitted centered on ωc; then emitted into the atmosphere, and the laser reacts with the atmosphere. The echo signal enters the receiving optical path through the telescope, and is sent through the beam splitter or the discriminator to detect by the detector. Based on different pollutants have different absorption cross sections, similar differential absorption lidar(DIAL), the λon and λoff can be determined. The lidar using the frequency comb light source can be easy designed into a compact structure, which is convenient to carry and maintain. It’s also a very advantageous for the lidar miniaturization and industrialization with a wide application prospect.
As the core component of lidar, APD detector is used to realize photoelectric conversion of laser echo signal. The detector needs to work at a stable temperature to ensure its application performance. A high gain amplifier circuit is designed. The temperature signal is collected by the MCU and the semiconductor refrigerator is controlled. The precision control of the temperature is realized through the PID algorithm. The adjustable high voltage module is integrated, and the APD bias voltage and temperature can be controlled through the serial port of the MCU. Reducing the volume of the APD detector, ensuring the wide temperature range of the detector and improving the integration degree of the lidar.
Because of the existence of blind zone and transition zone, the application of backscattering lidar in near-ground is limited. The side-scatter lidar equipped with the Charge Coupled Devices (CCD) can separate the transmitting and receiving devices to avoid the impact of the geometric factors which is exited in the backscattering lidar and, detect the more precise near-ground aerosol signals continuously. Theories of CCD side-scatter lidar and the design of control system are introduced. The visible control of laser and CCD and automatic data processing method of the side-scatter lidar are developed by using the software of Visual C #. The results which are compared with the calibration of the atmospheric aerosol lidar data show that signals from the CCD side- scatter lidar are convincible.
A system for collecting data of Side-Scatter lidar based on Charge Coupled Device (CCD),is designed and implemented. The system of data acquisition is based on Microsoft. Net structure and the language of C# is used to call dynamic link library (DLL) of CCD for realization of the real-time data acquisition and processing. The software stores data as txt file for post data acquisition and analysis. The system has ability to operate CCD device in all-day, automatic, continuous and high frequency data acquisition and processing conditions, which will catch 24-hour information of the atmospheric scatter’s light intensity and retrieve the spatial and temporal properties of aerosol particles. The experimental result shows that the system is convenient to observe the aerosol optical characteristics near surface.
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