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We demonstrate efficient generation of a mid-IR source at 3.2 microns using a PPSLT OPO with intracavity PPSLT difference frequency mixing (DFM) crystal. This wavelength is the best suitable for ultrasonic-generation in CFRP.

More than 300mW of 355nm generation was confirmed by cascaded configuration from 1064nm pulsed laser by using PP-LBGO (LaBGeO5) without walk-off. Measured temperature tolerances are 8.4 K-cm, which is almost double of Type-II LBO.

Second harmonic UV (350nm) generation was demonstrated by periodically poled LaBGeO5 (PPLBGO) for the first time. PP structures were fabricated with 5.5μm periodicity. The phase-matching-wavelength agreed fairly well with the calculation from reported Sellmeier’s equation.

Temperature-induced backswitching in near-stoichiometric LiTaO3 QPM devices was investigated. Backswitching consistently occurred due to heat treatment. We found two effective methods for fixing of fine periodically poled structure, they are edge-cutting method and ion implantation.

We investigated the saturation space-charge field by directly measuring photovoltaic current and photoconductivity in series of undoped (61 mol% Li2O in the melt) and Mg-doped (0.5, 1, 1.2,1.4 mol%) near-stoichiometric LiTaO3 crystals, where the two z-planes of crystals were coated with Au and a DC field was applied along the z-axis of the samples in a vacuum chamber. The wavelength (UV/visible) dependence of photovoltaic coefficient, specific photoconductivity, and saturation space-charge field were presented. The saturation space-charge field decreases with increasing the concentration of MgO and decreasing wavelength. The minimum space-charge field is only 40 V/m with the wavelength of 350 nm in the 1.4 mol % Mg-doped LiTaO3 because of huge increase of photoconductivity.

Near-stoichiometric LiNbO3:Tb, Fe crystals have three different types of energy levels suitable for two-color nonvolatile hologram recording. We investigated two-color multiplexed recording in the crystals. Hologram recording by use of 850nm recording beams and a gating light of visible wavelengths starting from the UV-pre-exposed colored state was suitable for multiplexing. By taking into account the dynamic behavior of sensitivity and erasure time constant owing to the gradual decrease of UV-induced absorption during writing, we could record 100 multiplexed hologram pages with nearly equal strength. An M/# of ~0.33 was obtained and the multiplexed holograms showed very stable nonvolatile readout characteristics.

We report that nearly stoichiometric LiNbO3 doped with small amount of MgO exhibit better material properties than conventional congruent crystals. Improvements are demonstrated with high photorefractive damageresistance at 532 nm to intensities as much as 8MW/cm2, low 180° ferroelectric domain switching field of 3.4 KV/mm, short absorption edge of 302 nm, and small scattering losses.