Observation of backward effective third-harmonic generation by cascading completely quasi-phase-matched backward second-harmonic and sum-frequency generation in periodically-poled potassium titanyl phosphate waveguide

摘要

Recently, we achieved backward second-harmonic generation (SHG) in periodically-poled bulk LiNbO{sub}3 (PPLN).1 We have improved the conversion efficiency by about an order of magnitude by using long laser pulses. Here, we report our new results of backward SHG by using periodically-poled potassium titanyl phosphate (PPKTP) waveguide. More importantly, we report our results on first observation of backward third-harmonic generation (THG) due to completely quasi-phase-matched cascaded SHG and sum-frequency generation (SFG) in PPKTP waveguide. This is the first time to achieve backward effective THG where both of SHG and SFG are quasi-phase-matched. Previously, we observed backward THG in PPLN by cascading SHG and SFG. However, only one of these two constituent processes is quasi-phase-matched.