Study of KTiOPO4 gray-tracking at 1064, 532, and 355 nm

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.