The Ld End-pumped Laser Crystal Thermal Effects And Characteristics Of Passively Mode-locked Study

Diode-pumped all-solid-state lasers(DPSL) has lots of advantages, such as compact structure, high stability and optical-optical conversion efficiency. It is widely used in national defence, photoelectron industry, communication, medical treatment and sanitation. Laser crystal is the core of diode-pumped all-solid-state lasers, which decide the output characteristics of laser. In recent years, in endeavoring to obtain higher output powers from continuous-wave end-pumped solid-state lasers, one must consider thermal effects that will impact optical performance. With the development of high power diode lasers, high power DPSSL has become one of the main objectives of current research and development activities within the laser community. Research of DPSSL has mainly concentrated on scaling of output power, while remaining of a high spatial beam quality. The main problem hindering scaling of diode-pumped solid-state lasers is heat deposition within the laser medium. The thermal effect of circular-face Nd:YAG, rectangular-face Nd:YVO₄ has been calculated. The focal length of the laser crystal is obtained by calculating the temperature and temperature distribution in the crystal. GaAs mode locking Nd:GdYVO₄ laser is set up and tested in this thesis. The contents can be outlined as follows:1. The history and progress of diode-pumped solid-state lasers are reviewed; and the characters of the diode-end-pumped solid-state laser are presented; then the dissertation presents the crystals of fitting diode-end-pumped.2. The thermal effect theory of circular-face laser crystal was analysed. By using this theory, the temperature distribution in laser crystal was obstained. The thermal conduct model of laser crystal was established.Using Possion equation, the temperature distribution in laser crystal was obstained, and the OPD induced by end-face deformation and total OPD were caculated. Based on the former calculation, we obtained the focal length of laser crystal with different pumping power. The experimental result was obtained, and it almostly coincides with the caculated result.For the first time, we obtained that end-pumped resonators with one highly reflective coating directly on the laser crystal can aggravate its thermal effect. The study shows that, for the solid-state laser with high power, the OPD induced by end-face deformation has a large influence on thermal effect of laser crystal. The thermal conduct model of cylindrical laser crystal was established.Using Possion equation, the temperature distribution in laser crystal was obstained with different Nd ion concentration and pumping radius.The study shows that in the same condition when the Nd ion concentration increase, the central temperature of Nd:YAG crystal's pumped face will rise and the temperature of crystal central axis will reduce faster. For the same ctystal, when the pumping radius decrease, the central temperature of Nd:YAG crystal will rise.3. Transient thermal profile in pulse and end-pumped anisotropic laser crystal had been firstly investigated numerically in this paper. By builting a thermal model with treatinig the repetitive thermal load as a square function of time, the dynamics of thermal buildup and temperature distribution in laser crystal was obtained. When the incidence pump power is fixed, The temperature distribution reachs the quasi-steady-state and remains the oscillatory behaviour, the repetitively oscillatory amplitude is inversely proportion to f . Adopt the means in , we can obtain the focal length of the crystal change with time, associate with the rate equations, the dynamics process of laser setup will obtained, this work is in progress. Although a Nd:YVO₄ crysal was taken for example in our calculations, the result suitable for other anisotropic laser crystal similarly.4. Passively Q-switched mode-locking Nd:GdYVO₄ laser is successfully demonstrated by using a piece of GaAs crystal grown at low temperature as the passively saturated absorber as well as the output coupler. The fundamental properties of Nd:GdYVO₄ laser are investigated. The maximum average output power of 3.5W are obtained by using plainsphere when the incident pumping power 10W, which corresponds to an optical-optical coversion efficiency of 35%; The threshold power for Q-switching mode-locked is 1.2W, the maximum average output power of 1.72W was obtained by using GaAs when the incident pumping power was 10W, mode-locked pulse train with a repetition rate of～113MHz was achieved. At the incident laser pumping power of 7W, Q-switching mode-locked with modulation depth is 100%.5. According to the principle of mode-locking and the performance of SBR, an one beam of light output laser equipment with SBR passively mode-locking Nd:YVO₄ laser is set up. A stable mode-locking laser output is obtained in experiment. The maximum average output power of 2.5 W is obtained at the pumping power of 10 W with the transmission of the output couple is 10%. The optical to optical conversion efficiencies is up to 28.6%.