| Ultraviolet laser has wide applications in processing dustry, detection, biological and other fields, due to its charaeters of shorter wave, good capability of focusing, high photon energy, small area of light spot, weak diffraction effects, high-resolution, etc. The current study of solid-state ultraviolet laser use double-frequency and sum-frequency to obtain high peak power UV laser output outside the resonant cavity, all traditional frequency technology is used single sum-frequency crystal for frequency conversion, there are some limitations in improving the UV output power and conversion efficiency, Therefore, this article proposed a scheme that use double sum-frequency crystal to achieve third harmonic generation to obtain UV. Based on this method, experiment used Nd:YAG crystal as gain medium,1064nm and 532nm through sum-frequency crystal achieved interaction outside resonant cavity, received 355nm UV light high peak output power. The main contents were completed as follow:(1)By comparing several common nonlinear crystals, selected the KTP crystal for double-frequency. On the basis of phase matching conditions of double-frequency and Conversion efficiency equation analyze the factors how to influence optimum length of KTP and how to improve double-frequency conversion efficiency in harmonic process.(2) By comparing several common nonlinear sum-frequency crystals, selected the LBO crystal for sum-frequency. On the basis of phase matching conditions of sum-frequency and frequency of three-wave coupled equations, analyze the feasibility of using double LBO to achieve the process of sum-frequency. Conversion efficiency equations of sum-frequency were combined, the relationship between single/double LBO optimal photon number ratio, fundamental laser beam divergence and walk-off angle with optimal crystal length and sum-frequency conversion efficiency were simulated in the process of sum-frequency. Calculated in theory, single/double LBO crystal achieved sum-frequency to produce different sum-frequency conversion efficiency in the output process of 355nm UV laser, and compared.(3) Based on the theory analysis of unit technology, experimental research was carrying on.355nm UV laser was obtained with maximum pulse energy 44.28mJ, pulse width 10.08ns, peak power 4.39MW, sum-frequency conversion efficiency (1064nmâ†'355nm) is up to 18.2%. |
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