Study On The Solide-state Broadband Tunable Laser And Its Application In Optical Gas Sensor

Nowadays,trace gas detection technology provides an effective method for the detection of trace gases.Due to its high discrimination and selectivity,optical gas sensor based on infrared absorption spectroscopy has been widely used in industry,medical and environmental pollution detection field.For these detection technology,the output power of the laser source directly determines the sensitivity and the minimum detection limit of the gas sensing system.The application of the solid laser source with high output power will be helpful to improve the gas detection capability of the optical sensing system.In addition,tunable solid-state lasers have the advantages of wide tuning range and narrow line width which can improve the selectivity of the sensor system.The beam quality of solid-state laser is higher,which will facilitate the optical system to couple the beam and reduce the optical noise.In optical gas sensing technology,the common laser source is semiconductor laser with low-power,and there are a few studies on optical sensing technology based on the wide-band tunable solid laser.Based on the above research background and significance,this paper is devoted to the study on the solid-state broadband tunable laser and its application in optical gas sensor.For this research,the broadband tunable solid-state laser which can be used in optical sensing technology was studied.the wavelength of the solid-state laser was selected as 2 ?m,covering the strong absorption spectrum of a variety of gases.The theory of the Tm:YAP laser with single longitudinal mode was analyzed theoretically.Then,the method of single longitudinal mode selection and frequency tuning of the laser are introduced.The research simulated the laser spectrum to determine the selection of the thickness and coating of the etlalons.The pattern matching of the pumping and oscillating light was analyzed by Zemax,and the structure parameters were determined,which lays a theoretical foundation for the experimental research.In the experiment of the solid-state laser,the output properties of the free-running Tm:YAP laser at 2 ?m were studied at first.The resonant cavity of the diode pump laser was selected as plane-concave cavity.Based on the results of the continuous-wave output properties,the stable and compact structure of the laser was designed by the SOLIDWORKS.Then,the output laser properties of the single longitudinal mode laser were studied experimentally.The frequency of the laser was coarse tuned by changing the angle of the etlalons.Near the gas absorption line,the frequency was fine tuned by controlling the temperature of Tm:YAP and the angle of the thick etalon.Scanning interferometer and wavemeter were used to measure the laser longitudinal mode and frequency.In the research of gas sensing technology,this paper firstly analyzes the theory of gas sensor system based on infrared absorption spectroscopy.Based on photoacoustic spectrometry?PAS?,the gas sensor system was set up experimentally,the laser soure of which was tunable solid-state laser studied in this paper.The intensity modulation of the input laser was carried out by a mechanical chopper.The microphone was used to convert the acoustic signal into an electrical signal,which was demodulated by the phase-locked amplifier to deduce the concentration of the measured gas?H₂O?.