Quasi phase matching through periodic step structure: modeling of frequency conversion in consideration of heat influence

摘要

Periodic inversion of spontaneous polarization in a ferroelectric substrate has realized quasi phase matching (QPM) and thereby revolutionized nonlinear optics. In this paper, we report on the heat influence on the frequency conversion in birefringence phase matching (BPM) by use of BaB_2O_4 (BBO) crystals as preparatory for efficient generation of the second harmonics (SHs) by QPM we suggest. Indeed, QPM is achieved normally by polarization inversion, but we suggest the periodic step structure to achieve QPM. Polarization inversion is generally formed by superimposed voltage. However, the shorter wavelength region is, the shorter inversion cycle is. Therefore, if the vacuum ultraviolet (VUV) region is treated, it becomes more difficult to form periodic inversion and the accuracy is more necessary. Accordingly, it is necessary to consider the influence of crystal's heat, caused by absorption of laser, which affects frequency conversion. We discuss validity of analytical approach about crystal's heat and frequency conversion by comparing between both results of experiment and simulation with BBO crystals.