Efficient third-harmonic generation in partly periodically poled KTiOPO4 crystal

A partly periodically poled KTiOPO4 (KTP) crystal has been designed to integrate quasi-phase-matched second-harmonic generation (QPM SHG) with sum-frequency generation in one crystal for generating a third-harmonic beam. The highest conversion efficiencies of 45% and 3% have been achieved in our experiments for QPM SHG and third-harmonic generation, respectively, by use of picosecond laser pulses at 1.327 mum. We have also discovered that periodically poled KTP has slightly different indices (n(z)) from bulk KTP. (C) 2001 Optical Society of America.