| In this thesis, the laser characteristic of different orientations of YAG crystal andthe grazing incidence slab amplifier were investigated. The thermal inducedbirefringence and depolarization of different orientations of Nd:YAG and passivelyQ-switched output performances with Cr4+:YAG were researched both in theory andexperiment. A compact grazing incidence slab amplifier was designed and the highefficiency amplified output was obtianed.In order to reduce the depolarization loss and achieve the high stable passivelyQ-switched output, the thermal induced birefringence and depolarization of Nd:YAGand the saturable absorption characterstics of Cr4+:YAG with different orientationswere studied, respectively. The methods of improving the stability of passivelyQ-switched output, and passively Q-switched performances of Cr4+:YAG wereresearched. Effect on passively Q-switched output performances with differentparameters, anisotropic absorption charactersitics and prepumping parameters wereanalyzed. To obtain high efficient, compact and low cost passively Q-switched laseramplifier, the slab amplifier structure and laser crystal parameter were studied. Thediode pumped grazing incident slab amplifier was investigated and optimized both intheory and experiment. The high efficiency, high average power, narrow pulseduration and high beam quality output was achieved. The specific contents are asfollows.1. The thermal induced birefringence and depolarization characteristics ofNd:YAG with different orientations. The thermal induced birefringence anddepolarization of [111]-,[100]-and [110]-cut Nd:YAG rod and slab was analyzed intheory. The anisotropic properities of [100]-cut Nd:YAG crystal was also investigated.The thermal depolarization performance and self-polarization output of diode pumped[111]-and [100]-cut Nd:YAG crystal were researched in experiment. The researchresults demonstrated that the [100]-cut Nd:YAG crystal has some anisotropicproperties, and the linearly polarized output can be greatly improved by using[100]-cut Nd:YAG crystal as the gain medium.2. Passively Q-switched characteristics of Cr4+:YAG with different orientations.The passively Q-switched mechanism of Cr4+:YAG crystal, the influence ofQ-switched output stability were researched. The effect of output stability on the performance of anisotropic absorption of Cr4+:YAG, and the effect of outputfrequency continuous tuning range on the performance of prepump parameters werestudied. The effect of output pulse charactersitics on the performance of output mirrorreflectivity and initial transmission of Cr4+:YAG were investigated. The impact of theQ-switching time and rate on output amplitude stability and frequency stability wereanalyzed in theory. The effect of output amplitude stability and extinction ratio ofpolarization on the performance of pump polarization were also studied. Based on theabove research, the repetition frequency of20kHz, average power of0.5W, pulseduration of2.3ns with high stability was achieved. The research results demonstratedthat the output amplitude stability and extinction ratio of polarization can be greatlyimproved by adjusting pump polarization. What’s more, the passively Q-switchedoutput performances were compared by using [111]-and [100]-cut Nd:YAG rod asgain medium,[001]-and [110]-cut Cr4+:YAG as saturable absorber. Based on the thisresearch, the repetition frequency of100Hz, pulse energy of8.5mJ, pulse duration of13ns, extinction ratio of polarization of800:1, and pulse stability of97.2%wasachieved. The research results demonstrated that the high stable and extinction ratioof polarization with less depolarization loss can be achieved by using [100]-cutNd:YAG as gain medium and [110]-cut Cr4+:YAG as saturable absorber.3. The grazing incidenct slab amplifier. The structure of slab amplifier wasdesigned firstly. The distribution of temperature gradient and thermal lens of slabamplifier were analyzed. According to the theoretical simulation and experimentalcomparison, the structure of slab amplifier and parameters of slab were optimized.The repetition frequency of20kHz, average power of20W, and pulse duration of2.3ns with high beam quality and high efficiency of diode pumped grazing incidenctslab amplifier was achieved. The output pulse energy unstability was lower than3%.According to the theory and experiment research, high efficiency, high extinctionratio of polarization and high stability output of diode pumped Nd:YAG/Cr4+:YAGpassively Q-switched laser could be achieved. What’s more, the high efficientamplified output could be obtained by using compact grazing incident slab amplifier. |
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