Optical studies of laser-induced gray-tracking in KTP

We have studied gray-tracking induced by a pulsed and polarized 532-nm lase r beam in flux grown KTiOPO4 (KTP) crystals. Transmission spectra measured under polarized light give different results: gray-tracking leads to an inc rease in the initial anisotropy of the linear optical properties of KTP, an d the polar axis is the most sensitive to this process. The dynamics of rel axation of gray-tracking is anisotropic and depends on the wavelength under analysis. We show a possible induced modification of the crystal surface a nd also the existence of an intensity above which gray-tracking reaches the saturation point. We then measure the temperature above which gray-trackin g no longer exists.