Photochromic ‘‘gray-track’’ damage occurring during 1064 nm second-harmonic generation (SHG) in KTiOPO4 is a significant limitation in many practical applications. Measurements of the evolution of gray-track damage during SHG, along with measurements of the 355 nm radiation simultaneously produced by non-phase-matched sum-frequency generation, are described. Comparison of these measurements with the gray-tracking induced by exposure to a single wavelength indicates that for the conditions investigated here, the gray-tracking during 1064 nm SHG is dependent only on the intensity of the 532 nm radiation. The dependence of the induced absorption on the 532 nm intensity is nonlinear, having a threshold of 80 MW/cm2, and an approximately linear increase for intensities above this threshold.

We report studies of photochromic damage induced in KTiOP04 single crystals by ultraviolet (UV) irradiation with peak intensities from 0.3 to 4.0 MW/cm'. The photochromic damage progressed to asymptotic values which were not linear with respect to UV intensity. Following UV exposure, transparency of damaged crystals recovered completely over tens of hours at room temperature, faster at elevated temperature. UV irradiation at significantly lower peak but higher average power did not produce damage. We also studied photochromic damage occurring during 1.064-pm second-harmonic generation. Fundamental infrared intensities ranged from 1.3 to 5.5 times larger than those producing highest nonlinear frequency conversion efficiency. Damage sites produced by the two methods exhibited similar absorption spectra.

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KTiOPO4 single crystals were grown from cerium-doped potassium phosphate fluxes. Cerium-doped crystals exhibited increased optical transmission relative to undoped material from the UV band edge to roughly 800 nm. Oxygen annealing was performed on undoped and cerium-doped crystals. The effects on transmission of oxygen annealing were qualitatively similar to those brought about by cerium doping although roughly five times smaller in magnitude. Cerium doping had no observable influence on the nonlinear optical coefficients but altered slightly the crystal’s birefringence.

LiNbO(3) waveguide substrates are terminated in out-of-plane 45 degrees -angled knife edges for the first time to our knowledge. This termination causes the guided wave to be totally internally reflected with excellent efficiency into or out of the waveguide surface, which allows new approaches for hybrid integration.