Study On Single-longitudinal- Mode Tm:YAG Ring Laser

2 ?m laser is eye-safe and it's at the absorption peak of water and CO2.What' more,2 ?m laser is located in the transparent window of the atmosphere.These advantages make the 2 ?m single-longitudinal-mode laser has important applications in narrow linewidth laser applications,such as doppler wind lidar,differential absorption lidar,high resolution spectroscopy,etc.In all single-longitudinal-mode laser implementation schemes,unidirectional ring laser based on faraday effect has obvious advantages in realizing narrow linewidth and wavelength tunable single-longitudinal-mode laser.The Tm3+-doped laser medium has a wider emission region in the 2 ?m band,which is conducive to achieving a tunable laser of wide range.Therefore,it is of great significance to study the single-longitudinal-mode Tm:YAG ring laser.Ceramics have many advantages over crystals,so,it is also meaningful to study single-longitudinal-mode ceramic laser.In view of this,the research of this paper can be summarized as the following.Firstly,the rate equations are established at the core of the quasi-three level system of the Tm:YAG laser.Based on the rate equations,the output characteristics of the Tm:YAG ring laser are numerically simulated,and the effect of the pump waist radius and the transmissivity of output mirror is given.The relationship between the thermal focal length of Tm:YAG crystal and pump parameter is studied by means of not only theoretical but also experimental measurements.Secondly,based on the working principle of the optical rotator,the realization method of unidirectional operation of ring laser is studied,and a scheme based on the coaction of an optical rotator,a half-wave plate and a mirror with polarized output is designed.The principle and numerical calculation in single-longitudinal-mode selection of Fabry-Perot(F-P)etalon are analyzed,and the appropriate thickness and tuning angle of the F-P are calculated.Using the ABCD law of Gauss beam and the stability requirement of the resonator,the design and demonstration of the ring cavity have been completed.Finally,the Tm:YAG ring laser is built,and the maximum output power is 930 m W under unidirectional operation.The optical-optical conversion efficiency and the slope efficiency corresponding to incident pump power are 6.84% and 11.9% respectively.The wavelength is 2014.06 nm,and the M 2 factor of the laser under maximum output power is about 1.10.The measurement of laser mode using scanning F-P interferometer shows that the output laser under unidirectional operation is single-longitudinal-mode.The insertion of F-P etalon in the cavity results in a wavelength tuning range of 2010.40 nm ~ 2017.59 nm(about 7.2 nm)and a power range from 673 m W to 872 m W.Using ceramic Tm:YAG as laser medium,the maximum output power of 363 m W is obtained under unidirectional operation,and the laser wavelength is 2014.47 nm.It is a singlelongitudinal-mode laser with a M 2 factor of 1.09.This paper is the first report on the single-longitudinal-mode Tm:YAG ring laser based on the Faraday effect.The highest power of wavelength-tunable Tm3+-doped single-longitudinal-mode laser is obtained at the same time.The study is of great significance in both academic research and practical application.