Investigation On The Influence Of Bbo Thermal-Induced Dephasing In266nm Ultraviolet Laser Conversion Efficiency

266nm UV laser has a wide range of applications in many fields of laser processing, medical, precision measure and others because of its advantages in wave length, small diffraction effects, high single-photon energy, and high resolution and so on. In the process of access to266nm UV laser by fourth harmonic using nonlinear crystals, nonlinear crystals will absorb part of the light energy. It induced the temperature rise in the direction of the light through in crystal, and destroyed the phase-matching conditions of BBO crystal that lead to phase mismatching. This effect severely restricted266nm UV laser output power and conversion efficiency. This thesis studied on the influence of BBO crystal thermal-induced dephasing in266nm UV laser conversion efficiency by theoretical analysis and experimental verification. The main research contents are as follows:(1) Based on heat conduction theory at first, the heat physical processes of BBO crystal in fourth harmonic were analyzed, and then the physical and mathematical models of temperature distributions that becaused by internal energy absorption were established. The temperature distributions of BBO crystal in fourth harmonic and the influence of different conditions were simulated by using MATLAB software.(2) For the temperature distributions in crystal, the processes of phase mismatching in BBO crystal with fourth harmonic were analyzed as well the physical and mathematical models of phase mismatching caused by temperature shift were established, and the phase mismatching distributions in the crystal were simulated. Double-frequency theory in combination on this basis, the influence of BBO crystal thermal-induced dephasing in266nm UV laser conversion efficiency was analyzed, the changes of the conversion efficiency were also simulated under different waist radius as well as the532nm input power.(3) Depending on the theories and simulations above, an experimental platform of266nm UV laser was set up for studying on the influence of BBO crystal thermal-induced dephasing in266nm UV laser conversion efficiency and the related experiments were studied on. Ultimately266nm UV laser was obtained with0.04W when the input power of the532nm laser was0.97W with the repetition frequency of10kHz and the pulse width of19ns, fourth harmonic conversion efficiency (532nmâ†'266nm) is4.12%.