| Mid-infrared (MIR) laser technology is widely used in many fields, such as atmospheric detection, military field, remote sensing technology and biological analysis, with hundreds of publications devoted to it in the few years. As the rapid development of PPLN and quasi phase matching technology, OPO PPLN has become the main direction of the research of mid-infrared laser technology, and it is the main method of the current generation of mid-infrared laser. Mid-infrared is a atmospheric transmission window, which 1.5-4.3 band covers many gas absorption peak and mid-infrared band belongs to the fundamental frequency of the gas absorption peak and absorption efficiency compared with near-infrared ultraviolet 2 to 3 orders of magnitude. The accuracy and the distance of the measurement can be greatly improved by using the mid-infrared absorption test. In this letter, we use the PPLN crystal to carry on the optimization design of the OPO cavity. Get the W level in the mid-infrared wide tuning (1.5-4.3 micron) output. At the same time, the DFB signal is amplified by the optical fiber amplifier, which is used as the source of the OPO pump, and the frequency of the output of the 2.6-4.3 micron can be swept. It is the first prototype in our country that can be frequency-sweep-able, wide tuning and high power output. We designed the engineering prototype, and successfully applied it to the tunable diode absorption spectroscopy (TDLAS) and demodulate the second harmonic signal.The main content of the thesis are as follows:1. Introduced the development of nonlinear laser, mid-infrared laser and gas detection.2. Elaborated the basic principle of optical parametric oscillator; explained the theories of the different types of the optical parametric oscillator; deduced the optical parametric oscillator threshold and gained conditions calculated wavelength tuning range; finished the theoretical design of cavity. In this paper, the principle of mid-infrared application in gas detection field is introduced, as well as the theoretical explanation of TDLAS detection method.3. Researched on the infrared and OPO cavity, and then, built the continuous ring cavity OPO in the experimental stage. Experimental design:the fiber amplifier as the pump source, multi-channel cycle MgO:PPLN for laser frequency conversion materials and analysis experimental results, laser measurement indicators:3.3 microns output power is 4W (pump 19W), laser linewidth (5MHz); wavelength tuning:idle frequency light, signal light 1.5-4.3 continuously tunable. and the output of the 2.6-4.3 micron can be frequency sweep able.4. On the basis of the above experimental results, we finished our engineering design, which included the design of laser optical path, the blessing of the lens, OPO motor position, furnace temperature control design and the elegant appearance design. In order to approve its stability, the overall temperature control and shock treatment had been taken into account. With this, it can be used in the scientific research and applied to many fields like environmental protection field, protection field and etc.5. Carried out the field gas absorption test with this prototype. Adopting the laser remote measurement, a telemetry platform is set up to test the remote sensing experiment of methane in 70m,400m,850m air. The results of the experiments are analyzed and it shows the detection accuracy is ppb.6. Summary and outlook. |
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