Study On Single-longitudinal-Mode Ho:YAP Ring Laser

2?m single longitudinal mode?single frequency?laser plays an important role in laser ranging,laser medicine,lidar and other fields.Because CO₂ has a strong absorption band in 2?m bands,2?m laser has another important application,that is,it can be used as differential absorption lidar and Doppler wind lidar seed laser.In order to satisfy the requirement of single longitudinal mode,high power and narrow linewidth,Ho:YAP ring laser is designed in this paper.To meet the requirement of narrow linewidth,a ring cavity with a cavity length of 1318 mm is designed;to meet the requirement of single longitudinal mode,the single longitudinal mode output of laser is realized by using the principle of optical rotator and half wave plate;and to meet the requirement of high power,Ho crystal with doped ions is used as working material.The specific research of this paper is as follows:Firstly,the advantages and disadvantages of several single-frequency output schemes will be analyzed by studying the status quo of these schemes,and then the scheme of inserting isolators?mainly composed of rotator?or acousto-optic Q into planar annular cavity will be put forward.Secondly,the properties of Ho:YAP crystal will be studied,the thermal expansion and thermal conductivity of Ho:YAP crystal will be analyzed,the energy level transition of Ho and the energy level rate equation will be established,the emission cross section and absorption cross section of Ho:YAP crystal will be studied,and the absorption and emission spectra of Ho:YAP crystal will be analyzed,which provides a theoretical basis for the following research.On the basis of the above research,the ring cavity of the laser will be studied.In order to meet the requirement of single longitudinal mode of single frequency laser,a rotator and a half wave plate are added to the ring cavity to make the single frequency output of the ring cavity laser.Therefore,the oscillation mode of the laser,the working principle of the rotator and the half wave plate are studied.Due to the requirement of wavelength tunability in differential absorption lidar,the single-frequency wavelength tuning is carried out by using standard gauge.The simulation of the inclination angle of standard gauge and standard gauge with different thickness is carried out,which provides a theoretical basis for wavelength tuning later.In order to meet the requirement of narrow linewidth of single-frequency laser,a four-mirror eight-shaped ring resonator with a total length of 1318 mm will be studied,and the spot size of the ring resonator with different crystal thermal focal lengths will be studied,so as to facilitate the later research.Finally,the experimental part of Ho:YAP ring-cavity laser will be started.The construction of ring-cavity laser will be studied.When the ring-cavity operates bidirectionally,the bidirectional output power of the crystal center under three different pumping faculae will be compared,and the bidirectional output power under three different output mirrors transmittance will be compared.The wavelength and Fabry-Perot?F-P?spectra of three different output mirrors are analyzed.The single-frequency power of three different output mirrors will be compared when the ring cavity operates unidirectionally.When the output mirror transmittance is 15%,the maximum single-frequency power is 345 mW,the beam quality factor?M ²?is 1.04,and the slope efficiency is 22.5%.When the maximum single frequency power is 345 mW,four kinds of gauges with different thickness are selected for wavelength tuning.Among them,the gauge with thickness of 0.3 mm has the largest wavelength tuning range,ranging from 2116.35 nm to 2119.75 nm.When the transmittance of the output mirror is 15%,the change of F-P spectrum is studied when the single-frequency wavelength is tuned under the standard gauge with thickness of 0.3 mm.It is concluded that the number and spacing of single longitudinal modes of F-P spectrum change with the change of wavelength.