Study Of Diode-pumped Doubly Q-switched Nd: GdVO₄ Lasers

In the same resonator, Actively Q-switched lasers with AO modulator can obtain stable pulse train output with high peak power and wide pulse duration; Passively Q-switched lasers with Cr⁴⁺:YAG saturable absorber can generate shorter pulse, but the pulse repetition rate is usually not very stable and the pulse peak power is lower. The Q-switched laser only with an AO modulator or Cr⁴⁺:YAG saturable absorber is known as single Q-switched laser. When an AO modulator and Cr⁴⁺:YAG saturable absorber are simultaneously used in the cavity, known as doubly Q-switched laser. It can obtain more symmetric and shorter pulse with stable repetition rate and high pulse peak power. In this doubly Q-switched laser, the AO Q-switch is used to control the pulse repetition rate and allow the laser medium to store energy to ensure that the population inversion is fully saturated. The Cr⁴⁺:YAG saturable absorber is used to generate shorter laser pulse through the nonlinear saturable absorption characteristics. The dissertation presents the characteristics of the pulse obtained from the purely and doubly Q-switching laser of ground frequency,the doubly Q-switching laser of doubly frequency. The continent of the dissertation is as follows:1. The history and development of diode pumped solid state Q-switched lasers are reviewed. The advantages of doubly Q-switched laser are summarized. The Q-switched technology is summarized from all round. The main continents of the dissertation are discribed briefly.2. Characteristics of Nd:GdVO4,Cr⁴⁺:YAG saturable absorber and AO Q-switcher are researched, and their important parameters are given at the meantime. The theory of the AO Q-switched and the rate equation of passively Q-switched laser considered the Gaussian spatial distribution of the photon density is given. Some experiments are made about LD end-pumped Nd:GdVO4 AO Q-switched laser and passively Q-switched laser of 1064 nm, some researches about pulse width, average output power, peak power are presented, some conclusions are received. 3. The rate equation of doubly Q-switched laser is given when the spatial variations of the population-inversion density of the gain medium, the ground-state poulation density of the SA, the Gaussian spatial distribution of the photon density, the turnoff time of the AO Q-switch are considered. Theoretical analyses about pulse width is presented, and compared with the pulses of purely AO Q-switched and passively Q-switched lasers. Some experiments are made about LD end-pumped AO,Cr⁴⁺:YAG doubly Nd:GdVO4 laser of 1064 nm. When the incident pump power is 7.7 W, the repetition rate of AO is 10 kHz, the transmittance of output coupler is 20% at 1064 nm, the initial transmittance of Cr⁴⁺:YAG is 70%, the shortest pulse width of 18 ns is obtained. And the shortest pulse profiles of the three kind Q-switched lasers are compared.4. Some researches and analysis about frequency doubling and phase matching are made. Characteristics of nonlinear frequency doubling crystal KTP is researched. Some experiments are made about LD end-pumped doubly Nd:GdVO4/KTP,AO Q-switcher and Cr⁴⁺:YAG green laser of 532 nm for the first time. The pulse width,average output power,peak power of the experiments are researched.