Research On Short Pulse Width High Repetition Frequency Slab Laser Amplifier With Bounce Geometry

High energy, high repetition frequency, short-pulsed solid state lasers have many advantages over processing including small thermal effected areas, high processing efficiency, lower cost, etc. Thus, they are widely applied in laser processing, nonlinear optics, medical tests and so on. However, since the gain for amplified spontaneous emission?ASE? is inversely proportional to the pulse duration and the severe thermal effects at high frequency repetition?larger than 1 kilohertz?, it is difficult for solid state lasers to obtain the laser outputs with high pulse energy, short pulse width?short to 1 nanosecond?, and high frequency repetition simultaneously. Thus, study on realization of high-energy, high-frequency-repetition, short-pulse-width solid state lasers has the important significance for practical applications.The research status of high energy short pulsed slab lasers at home and abroad was investigated and analyzed. Master Oscillator Power Amplifiers?MOPA? was selected as the way to achieve the goals. Study on the multi-passed amplification of high energy, high repetition frequency, short pulsed lasers based on bounce Nd:YVO₄ was accomplished. The pulse energy of 1mJ was obtained at a pulse repetition frequency of 7kilohertz and the pulse duration?FWHM? of 1.2ns. The main contents of this thesis were included as follows,Given amplified spontaneous emission?ASE?, the angle designed for multi-passing, the thermal effects, the geometrical shape of the bounce Nd:YVO₄ was designed. In order to cool the crystal effectively, bounce Nd:YVO₄ crystal was welded between two large heat sinks on its two vertical big non-light-passed surfaces.In order to obtain the amplified signal outputs with high gain, the multi-passed optical transforming system was designed. The side pumping with LD was adopted. The experiments of single-stage three-passed amplification were exercised.Based on the experimental results, the optimizations of the way of pumping and the methods of restraining ASE were achieved. The heat input was decreased by 30% by converting the Continual-Wave?CW? pumping to pulsed pumping. Besides, the power of ASE in the output of third-passed amplification was restrained from 4 watts down to 0.4 Watts by setting stops to lower the power density of pumping and to separate the optical paths within the pumping region, suppressing the effect of gain grating responsible for the increase of ASE.In order to restrain self oscillations?self excited emission oscillates between the inner surfaces of the crystal? in the crystal, Germanium with high absorption efficient in NIR region was sputtered on the non-light-passed surfaces of the crystal. The experimental studies on the effect of restraining self oscillations in crystal with and without Germanium was carried out and compared. The pulse energy of the passive Q-switched oscillator with Germanium-sputtered Nd:YAG was improved by 75% compared with that of the passive Q-switched oscillator with non-Germanium-sputtered Nd:YAG at the pump current of 67 A.