Study for environmentally-friendly wavelength-converted ultraviolet laser

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We here investigate the fabrication technology of fine-period twins in quartz for quasi-phase-matched wavelength conversion to VUV light. To form fine stable twins, it is essential to reduce the stored elastic energy in stress application because the energy triggers backswitching (BS) of the formed twins. For estimating the energy stored in twin walls, we developed a method to measure BS stress. If we use the sufficiently low decreasing rate, the BS stress is turned out to be lowered by 50% as the temperature decreases. The extrapolated curve indicates the BS stress should be lower than zero, meaning twins could survive even at zero stress. The guideline is established for stabilization. We also measured the coercive stress for twins and obtained the step width dependence of the stress. As the step width becomes narrower, more stress is required for switching. Furthermore, we designed and fabricated stress-maintaining module and achieved stable fine twin structures with 9.6 um period.