Ultrafast induced absorption dynamics in flux-grown KTiOPO/sub 4/

Summary form only given. KTiOPO/sub 4/ (KTP) is a ferroelectric nonlinear optical crystal with large second-order nonlinearities and it is attractive for fabrication of quasi-phasematched structures, suitable for frequency conversion applications throughout the visible to mid-infrared optical spectrum. However, experiments employing high-intensity visible light have revealed formation of color-centers in KTP, with broad absorption spectrum spanning from below 400 nm up to 650 nm and the relaxation time of the order of tens of minutes. The color-center formation has been attributed to the capture of free electrons and holes by the native defects (Ti/sup 4+/-Vo) and impurities (Fe/sup 3+/), respectively. We report on the femtosecond time-resolved transmission spectroscopy in KTP which revealed surprisingly large absorption increase over a broad spectral range in the visible, induced by the ultraviolet (UV) pump, and the full recovery of only 1.2 ps.