| Summary: | 碩士 === 國立清華大學 === 光電工程研究所 === 93 === Because of the thermal-lensing effect, it is very difficult to keep the stability of the laser beam’s divergence angle in a high power solid state laser. With the increase in the input pump power, the thermal-lensing effect becomes severe.
This thesis discusses the stability of Nd:YAG and Nd:YVO4 in the resonance cavity. A stimulation program was built to predict the heat source formula in the crystal with the methods of Fresel’s propagation and Gaussian beam ABCD matrix method. We can, therefore, find the temperature profile in the crystal and calculate the focal length of the crystal after different time durations. Finally we discuss the stable condition of resonance cavity with the presence of the induced thermal-lensing effect. Under the input pump power of 0.5W, the induced focal length of Nd:YAG and Nd:YVO4 are estimated to be 431 m and 164 m, respectively. Therefore, we conclude that thermal-lensing effect has a greater impact on the laser systems based on Nd:YVO4 than on Nd:YAG.
On the other hand, to improve the lasing efficiency and stability, the heat dissipation structures are often required on the crystal. The comparison of the thermal-lensing effect with and without the heat dissipation structure is also presented.
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