OPTICS COMMUNICATIONS

A periodically-poled flux-grown KTP crystal was used for first order quasi-phase-matched (QPM) second harmonic generation of a Nd:YAG laser. The normalized conversion efficiency of the 1 cm long, 0.5 mm thick sample was 1.28% W-‘. A lower limit on the nonlinear coefficient of KTP, d,, 2 14.9) 1.5 pm/V was derived from these measurements. The temperature and wavelength tuning coefficients near 1064 nm were determined. The same device was also used for third order QPM frequency doubling of 784 nm light, and the normalized conversion efficiency in this case was 0.12 % W- ‘. 0 1997 Elsevier Science B.V. Quasi-phase-matched second harmonic generation is achieved by periodic reversal of the sign of the nonlinear coefficient to compensate for the phase velocity mismatch between the fundamental and second harmonic waves [I]. The main advantages of QPM nonlinear processes are higher efficiency obtained by choosing the larger, diagonal elements of the,$‘) tensor which are not accessible to birefringent phase-matching and the possibility to noncriti