Fourth harmonic generation of DKDP crystal

Deuterated dihydrogen phosphate(DKDP) crystals of different deuterium contents were cut for type-I non-critical phase-matching with the direction at 90 to the crystal z axis and at 45 to the crystal x axis， and then measured in the fourth harmonic generation experiments with fundamental wavelengths of 1 064 nm and 1 053 nm， respectively. The optimum deuterium content of DKDP crystal was confirmed by measuring the relation between deuterium content and phase-matching angle. The results indicate that DKDP crystal can not achieve non-critical phase matching by adjusting its deuterium content at room temperature with the fundamental wavelength of 1 064 nm. However， at the fundamental wavelength of 1 053 nm， the optimum deuterium content of DKDP crystal is 85%， to achieve non-critical phase matching at room temperature.