Theoretic Study On The Thermal Effects Of Solid-state Lasing Medium

High-Power solid-state lasers are of major interest for applications in materials processing and science research because of some advantages, such as high power scaling, high peak power, compact devices and the wavelength in the IR delivery through an optical fiber which is one of the major advantages of solid lasers when compared to CO2 lasers. However it is difficult to design a high power laser with good beam quality because there are thermal effects in the active medium. Thermal effects in the active medium are investigated systematically in this dissertation to improve the working characteristics of lasers, increase output power and improve beam quality. The main content of the research in this dissertation is composed of five parts: 1. Introduction. 2. Thermal effects in the rod active medium of solid lasers. 3. Thermal effects in the non-rod active medium of solid lasers. 4. Diffraction integral equations of toroidal-spherotoric mirrors resonator and the new method to solve the thermal effects in the tube laser. 5.Conclusion.1. In the part of introduction, the advantages of solid-sate are presented and the state of the development and research on the high power solid-state lasers and thermal effects in active medium are mentioned. Then the main content and purpose of this dissertation is given.2. The thermal effects of rod solid-state are studied. The active medium and the pump are analyzed and the origin of the thermal effects is opened out. Through studying the temperature distribution, stress distribution, refractive power and birefringence, the fact that the un-uniformity of temperature distribution is the origin of thermal stress, thermal lens and thermal birefringence is disclosed. To reduce the thermal effects, the un-uniformity of temperature distribution and the heat in the active medium should be lessened. Some thermal compensation methods such as rotator and self-adjusting lenses are mentioned.3. Geometry of active medium such as tube, disc and slab has advantage to decrease thermal stress, increase output power and improve beam quality. The temperature of inner wall and outer wall severely infect beam quality, and the cooling of the interface of tube laser should be enhanced. Pre-stress added on outer wall of tube can improve stress distribution, decrease stress and increase output power. Similarly tube self-adjusting lens is exploited to compensate for thermal lens. 4. In the same approximate manner as usual spherical mirror resonator (SMR), diffraction integral equations of toroidal-spherotoric mirror resonator (TMR ) that its axes are cylindrical distribution have been derived from Kirchoff-Fresnel integral formula. For designing optimum resonator and researching transverse mode of tube lasers, the equations of TMR provide the mathematical model. 5. We make conclusion on the whole study and prospect the following research on this study.In this dissertation, a good thought to resolve thermal effects of solid-state laser is mentioned, and a new idea to design a high-power solid-state laser with good beam quality is given.