Thermally induced dephasing in periodically poled KTP frequency-doubling crystals

Abstract

A thermally induced spatial and temporal dephasing model of second-harmonic generation has been developed to describe the conversion efficiency and its degradation of periodically poled potassium titanium phosphate (PPKTP) in a cw, single-pass frequency conversion system. The model confirms the experimental data that show that second-harmonic power greater than 800 mW (15 kW/cm2) causes two-photon nonlinear absorption, leading to time-dependent photochromic damage in PPKTP. This added absorption degrades the conversion efficiency from an initial value of 19% to an unrecoverable asymptotic value of ∼8% in 2 h at 145 kW/cm2 of pump intensity through thermal detuning phase mismatch.