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

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Abstract
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.