The Experimental Researches Of Passive Q-switched Laser By LD Pumped

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. Cr⁴⁺:YAG crystal was invented in 1988. It is a new type laser crystal in near infrared ray. Its emission range is between 1.3¹.6μm. Cr⁴⁺:YAG crystal has good capability of heat exchange, steady physical and chemical character. It can generate passive Q-switching, passive mode-locking, self mode-locking by continuous or pulsed pumped. Cr⁴⁺:YAG crystal is attractive in light communications, medical applications, laser technology field.In this dissertation, by using the fiber-coupled laser-diode as the pump source, Nd:YVO₄ and Nd:YVO₄/YVO₄ composite laser crystls as the gain mediums, we have studied the performance of the output pulse width control in the passively Q-switched lasers with Cr⁴⁺:YAG and GaAs saturable aborbers, respectively. Meanwhile, the coupling wave rate equations are given to theoretically analyse the properties of the above-mentioned Q-switched lasers.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%.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%. 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 9.6 W was obtained at the pumping power of 26 W with the transmission of the output couple are 24% . The optical to optical conversion efficiencies was up to 36.9%.The thermal effect in rectangle-section laser crystal by high power eccentric-end pumped was investigated. And the eccentricity of rectangle-section (ERS) laser crystal eccentric-end-pumped was defined. The temperature field and temperature gradient field influenced by the ERS of diode laser were obtained by solving the poisson equation. Compared to the centre-end-pump, the maximal temperature fall ,the temperature gradient rise with the ERS increasing and the maximal thermal distortion will be migrated and strengthened, respectively.