Abstract
Noncritical type‐I phase matching at room temperature has been observed in KNbO3 for λpm=860 nm using the nonlinear optical coefficient d32=−40‖d11 (SiO2) ‖. By increasing the crystal temperature up to 180 °C the phase‐matching wavelength is increased to λpm=950 nm. At room temperature the efficiency for second‐harmonic generation was 15% for a power density Iω =0.5 MW/cm2 of the fundamental and for a crystal length l=5.74 mm.