Backward second-harmonic and third-harmonic generation in a periodically poled potassium titanyl phosphate waveguide

We observed backward second-harmonic and backward third-harmonic generation in a periodically poled KTiOPO4 waveguide using nanosecond laser pulses. T he highest conversion efficiency achieved for the backward second-harmonic generation, occurring at the 25th-order grating, was similar to 0.6%. The b ackward third-harmonic generation was the result of mixing the pump beam wi th the forward or the backward second-harmonic beam. Conversion efficiency of similar to 0.4% was achieved at a pump wavelength of 1233.7 nm, where th e two constituent nonlinear processes are both quasi-phase matched. (C) 199 9 Optical Society of America.