Wide acceptance angle of second harmonic green generation by periodically poled potassium niobate

Summary form only given. Potassium niobate (KN) is expected as a nonlinear crystal for the high-power green laser, since it does not show optical damage under high power density at room temperature. However, its critical phase matching suffers from narrow angle acceptance (/spl Delta//spl theta/ = 0.03 deg/cm), which deteriorates the transversal beam shape. We fabricated periodically poled potassium niobate (PPKN) for green generation and SHG characteristics were compared with the conventional angle-cut KN (/spl theta/ = 71, /spl phi/ = 90, L = 5 mm). Additional 90-degree thin domain walls were generated near the pattern edge. The angle /spl theta/ acceptance was 0.96 deg/cm which was 38 times wider than that of angle-cut KN (0.025 deg/cm). The beam shape was almost circular in contrast to the highly elliptical one for the angle-cut KN. No photorefractive or other degradation was observed at room temperature. No degradation was observed under a high power intensity Q-switched Nd:YLF laser with power under peak power density 200 KW/mm/sup 2/ at 1 kHz.