We observed backward second-harmonic and backward third-harmonic generation in a periodically poled KTiOPO<sub>4</sub> waveguide using nanosecond laser pulses. The highest conversion efficiency achieved for the backward second-harmonic generation, occurring at the 25th-order grating, was ~0.6% . The backward third-harmonic generation was the result of mixing the pump beam with the forward or the backward second-harmonic beam. Conversion efficiency of ~0.4% was achieved at a pump wavelength of 1233.7 nm, where the two constituent nonlinear processes are both quasi-phase matched.
© 1999 Optical Society of America
Xinhua Gu, Maxim Makarov, Yujie J. Ding, Jacob B. Khurgin, and William P. Risk, "Backward second-harmonic and third-harmonic generation in a periodically poled potassium titanyl phosphate waveguide," Opt. Lett. 24, 127-129 (1999)