Research On All-solid-state Tm:YAP Laser

The 2μm laser is in the atmospheric window,human eye safety,strong absorption of water molecules and polymer materials,etc.Therefore,the 2μm laser has a wide range of uses in medical treatment,atmospheric monitoring,lidar,laser processing and other fields.At the same time,in scientific research,the wavelength of 2μm laser can be extended to 2-5μm through optical parametric oscillation technology,which is of great research significance as a pump source for 3-5μm laser.Therefore,the all-solid-state Tm:YAP laser is studied in this paper.The main work is as follows:（1）The characteristics of Tm:YAP laser crystal were studied.According to the energy level structure of Tm:YAP laser crystal,the rate equation of Tm:YAP CW laser is analyzed.The thermal lensing effect of Tm:YAP laser crystal was studied,and the change of thermal focal length of Tm:YAP crystal under different conditions was calculated by MATLAB software.And the experimental measurement method of the thermal focal length of laser crystal is summarized.（2）Two types of Tm:YAP CW lasers with a convex-concave cavity and a flat-concave cavity were experimentally built.When the pump power of the convex-concave cavity laser is about 6 W,the laser reaches the threshold of light output.When the pump power is increased to 16.5 W,the laser output maximum power is 3.33 W,the slope efficiency is 28.7%,and the stability of the output power can reach 0.92%.When the pump power of the plano-concave cavity laser is about 6 W,the laser reaches the light output threshold.When the pump power rises to 13 W,the laser output maximum power is 2.13 W,the slope efficiency is 27.8%,and the output power stability is 2.25%.Comparing the two groups of experiments,it is found that the laser output efficiency of the convex-concave cavity is higher and the stability is better.Selecting a better convex-concave cavity laser to measure the spectrum and spot shape of the output laser,The central wavelength of the output light is 1997 nm～1999 nm,and the spectral width at half maximum is 5.18 nm.The light spot is approximately circular and belongs to the TEM₀₀mode.（3）Research on SESAM mode locking principle and dispersion and dispersion compensation.The variation of the nonlinear refractive index on SESAM with the pulse flux on SESAM under different conditions is calculated.The Tm:YAP crystal is anisotropic,and the second-order dispersion of the three axes of the Tm:YAP crystal in the 2μm band was calculated,all of which were negative.After calculation,it can be seen that the dispersion produced by the silicon prism pair in the 2μm waveband is positive,and the second-order dispersion produced by the silicon prism when the distance L between the vertices of different prism pairs is calculated.When L=63μm,the second-order dispersion produced by the silicon prism pair and Tm:YAP crystal is similar in value.（4）Design of Tm:YAP mode-locked laser.Firstly,the stable region of the convex-concave cavity laser built in the experiment and the radius distribution of the spot in the cavity are simulated;In addition,for the mode-locked folded cavity laser,the effects of the L1 and L2 lengths,folding angles,and thermal focal lengths on the folded arm on the stable area and the spot size on the SESAM were simulated.Finally,the light spot distribution at each position in the folded cavity is obtained.