Femtosecond-pulse cavity-dumped solid-state oscillator design and application to ultrafast microscopy

The construction, modeling, and performance characteristics of a new resona tor design for ultrafast cavity-dumped oscillators are presented. An acoust o-optic Bragg cell was incorporated at the end of the longer arm of a Ti:sa pphire oscillator rather than in the shorter arm as in several recent studi es. The new arrangement improves the pulse intensity stability of the oscil lator and significantly reduces the effort required in construction. The ex perimental findings are supported by comparison of the stability regions of the laser cavities based on the two different designs. To demonstrate the potential of cavity-dumped oscillators for spatially resolved ultrafast spe ctroscopy studies, the pulse duration is characterized at the focal plane o f two achromatic high-N.A. oil-immersion objectives with different amounts of flat-field correction. Transform-Limited pulse widths as short as 15 fs are obtained. To our knowledge, this is the shortest pulse duration measure d with true high-N.A. (N.A. > 1) focusing conditions. (C) 1999 Optical Soci ety of America OCIS codes: 110.0180, 140.4050, 140.3410, 140.7090, 300.6530 .