Study On Characteristics Of Laser-diode-pumped Electro-optic Q-switched And Doubly Q-switched Laser

Laser-diode pumped solid-state lasers have wide applications in the fields such as telecommunication, detection, medical, military and information processing, due to its advantages such as all solid state, simplicity, stability, high efficiency and beam quality.Electro-optic (EO) Q-switch is essential component of the pulsed laser. A reasonable selection of EO materials is the effective approach of improving performance on Q-switch. A beta barium borate (β-BaB₂O₄) crystal has been used to EO Q-switch laser-diode pumped solid-state lasers, resulting in stable, low insertion losses, high laser damage threshold and average power operation.In this dissertation, by using the fiber-coupled laser-diode as the pump source, YVO₄/Nd:YVO₄ crystals as the gain mediums, BBO EO modulator and Cr⁴⁺:YAG saturable absorbers as Q-switch, and typeⅡphase-matching KTP crystal as frequency doubling crystal, we have studied the performance of the actively Q-switched laser, doubly Q-switched laser, and intracavity frequency doubled doubly Q-switched Laser, respectively. In addition, the research on beam quality of doubly Q-switched laser has been carried out. Meanwhile, the coupling rate equations under Gaussian wave approximation have been established to theoretically analyze the properties of the above mentioned Q-switched lasers. The main contents of this dissertation include:1. Laser-diode pumped actively Q-switched YVO₄/Nd:YVO₄ 1064 nm laser by using BBO EO modulator has been realized. At the maximum incident pump power of 15 W and the pulse repetition rate of 2 kHz, the obtained single pulse energy and the pulse duration are 0.93 mJ with and 9.9 ns, respectively, corresponding the pulse peak power 93.64 kW. (2.1)2. Considering the time function of EO modulator, the transversal and longitudinal distributions of the intracavity photon density, the population-inversion density, a new rate equation model describing the run of actively Q-switched laser with EO modulator has been established. The numerical solutions of the equations are consistent with the experimental results. (2.2)3. Using the plane-plane cavity, laser-diode pumped doubly Q-switched YVO₄/Nd:YVO₄ 1064 nm laser with both BBO EO modulator and Cr⁴⁺:YAG saturable absorber has been realized. At a maximum incident pump power of 15 W and an EO Q-switch repetition rate of 2 kHz, the stable laser pulses with the pulse duration 4.3 ns and the pulse peak power 74.42 kW are obtained. Considering the ground-state population density of Cr⁴⁺:YAG saturable absorber, the theoretical analysis has been performed and is consistent with the experimental results. (3)4. Using the three-mirror-folded cavity, laser-diode pumped doubly Q-switched YVO₄/Nd:YVO₄/KTP 532 nm green laser with both BBO EO modulator and Cr⁴⁺:YAG saturable absorber has been realized. Considering the nonlinear loss due to the intracavity second harmonic wave conversion, the theoretical analysis has been performed and is consistent with the experimental results. (4)5. We have developed a laser beam parameters analyzer based on area array sensor to measure M factor for laser-diode pumped solid-state lasers. The experimental results match the theoretical prediction. (5)The main innovations of this dissertation are as follows:1. We have firstly presented the performance of laser-diode pumped doubly Q-switched YVO₄/Nd:YVO₄ 1064 nm laser with both BBO EO modulator and Cr⁴⁺:YAG saturable absorber experimentally and theoretically.2. Laser-diode pumped doubly Q-switched YVO₄/Nd:YVO₄/KTP 532 nm green laser with both BBO EO modulator and Cr⁴⁺:YAG saturable absorber has been presented experimentally and theoretically for the first time.