Ld Pumped All-solid-state Laser Thermal Effect And Mode-locking Characteristics Of Study

High power diode pumping all-solid-state lasers have recently attracted much more interest for their unique merits, such as long lifetime, compact structure, high stability and optical-optical conversion efficiency, etc. It employs diode laser as the pump source instead of conventional Helium or Xenon flashlamp, leading to a significant improvement of efficiency, reliability and beam quality, and thus called the revolution of the laser history. 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 theory of thermal effects and a comparison of thermal characteristics between conventional cystal and compositve cystal are detailed investigated. The focal length of the laser crystal is obtained by calculating the temperature and temperature distribution in the crystal. SESAM cw-mode loking Nd:GdYVO₄ and Nd:YVO₄ lasers are set up and tested in this thesis. The contents can be outlined as follows:1. Large thermal gradient arises from the heat deposition within a very small volume near the pumping facet of the laser crystal in longitudinally pumped system, resulted in thermal lensing and strongest aberrations at the pumping facet. Low temperature reservation of the pumping surface and the crystal body could be adopted to relieve thermal effects and improve laser performance. This can be done by using diffusion bonding of doped laser crystal to a nondoped crystal. The focal length and the temperature distribution in the Nd:YVO₄/YVO₄ composite laser crystl are obtain theoretically based on the numerical heat analysis to the end-pumped anisotropic laser crystal, The end-pumped Nd:YVO₄/ YVO₄ composite crystal laser was set up and tested with z cavity for evaluating the above calculation, The maximum output power of 9.87 W at 1064 run was obtained at the pumping power of 16.5 W. The highest optical-optical conversion efficiencies were up to 60% at 1064nm.2. The structure of a passive mode-locking device LT-GaAs is discribed and its performance of Q-switching mode-locking is invested by using a Nd:YVO₄/YVO₄ composite crystal. Q-switched mode-locking pulse with modulation depth of 100% was available. The output power of 2.2 W was achieved at the pumping power of 14 W, and the optical to optical efficiency was 15.7%.3. The structure of a passive mode-locking device LT-InGaAs is discribed and its performance of mode-locking is examined by using a Nd:YVO₄ as laser crystal. The threshold power for Q-switching and Q-switched mode-locking were 2 W and 3.1 W respectively. Q-switched mode-locking pulse with modulation depth of 100% was available at the incident pumped power of 5.6 W. The Q-switching envelope with repetition rate of 62.5 KHz and pulse duration of 600 ns was obtained. At 6.4 W of the incident pumping power, stable cw mode locking with a 5.1 pulse duration at a repetition rate of 113MHz was detected. The output power of 2.29 W was achieved at the pumping power of 12 W, and the highest optical to optical efficiency was 19.1%.4. 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. The problem of conventional laser of two beams output has been solved. A stable mode-locking laser output is obtained in experiment. The maximum average output power of 1.6 W and 2.5 W were obtained at the pumping power of 10 W with the transmission of the output couple are 3% and 10% respectively. The optical to optical conversion efficiencies were up to 16% and 25%.5. The broader fluorescence emission spectrum bandwidth of Nd:Gd_xY_1-xVO₄ is～2nm, double as Nd:YVO₄(Gd:YVO₄), Nd:Gd_xY_1-xVO₄ has a relatively smaller emission cross-section and a longer upper-level lifetime, which might lead to attendency for the laser to be driven into the Q-switched mode-locked regime with a mode-locked pulse in a Q-switch envelope. Using GaAs crystal grown at low temperature as the output couple, the characteristic of OML and ML Nd:Gd_0.5Y_0.5VO₄ laser is studied. At 6.4W of the incident pump power, stable continuous-wave mode locking with a 5.1 pulse duration at a repetition rate of 113 MHz was detected. The average output power is 1.49W. The maximum average output power of 2.29W and optical to optical efficiency was 24.8% are obtained at the pumped power of 12 W.