SUB-20-FS PULSES TUNABLE ACROSS THE VISIBLE FROM A BLUE-PUMPED SINGLE-PASS NONCOLLINEAR PARAMETRIC CONVERTER

Femtosecond pulses with center wavelengths between 470 and 750 nm are generated in a single-stage type I BBO optical parametric amplifier pu mped by a frequency-doubled 1-kHz Ti-sapphire amplifier. A high-qualit y white-light continuum is used as the seed. Pulse durations as short as 16 fs and pulse energies of as much as 11 mu J are observed. The qu antum efficiency is similar to 25% for both 7- and 40-mu J pump pulses . This unique combination of ultrashort pulse duration and high conver sion is made possible by noncollinear phase matching that permits a su fficiently large amplification bandwidth. Simultaneously the group vel ocities of the signal and the idler are effectively matched. As a resu lt widely tunable sub-20-fs pulses can be generated in a nonlinear cry stal as thick as 2 mm. (C) 1997 Optical Society of America.