Ultraviolet generation by first-order frequency doubling in periodically poled KTiOPO4

First-order quasi-phase-matched frequency doubling at 780 nm in a 1-mm-thic k periodically poled KTiOPO4 crystal with an inverted-domain period of 2.95 mu m has been demonstrated for the first time to the authors' knowledge. A normalized conversion efficiency of 1.1% W-1 cm(-1) has been obtained in c w mode. Experiments show that group-velocity walk-off prevents efficient fr equency doubling of femtosecond pulses in KTiOPO4 in the UV spectral range. However, because of the large optical nonlinearity, periodically poled str uctures can be efficiently used for frequency doubling of cw and pulsed las ers with pulse lengths as short as similar to 1 ps. (C) 1998 Optical Societ y of America.