Ultraviolet generation by first-order frequency doubling in periodically poled KTiOPO_4

First-order quasi-phase-matched frequency doubling at 780 nm in a 1-mm-thick periodically poled ${\mathrm{KTiOPO}}_4$ crystal with an inverted-domain period of $2.95 \mathit{\mu }\mathrm{m}$ has been demonstrated for the first time to the authors’ knowledge. A normalized conversion efficiency of $1.1\% {\mathrm{W}}^{-1} {\mathrm{cm}}^{-1}$ has been obtained in cw mode. Experiments show that group-velocity walk-off prevents efficient frequency doubling of femtosecond pulses in ${\mathrm{KTiOPO}}_4$ in the UV spectral range. However, because of the large optical nonlinearity, periodically poled structures can be efficiently used for frequency doubling of cw and pulsed lasers with pulse lengths as short as $\sim 1 \mathrm{ps}$.