Abstract

We discuss our new femtosecond laser source which is tunable from the deep red to the mid-infrared.¹ This is the first cw-modelocked singly resonant optical parametric oscillator and, we believe, the most broadly tunable femtosecond (or cw) laser in existence. It is based on parametric conversion in KTiOPO₄ in a singly resonant, dispersion-compensated, and actively-stabilized cavity² which is sync-pumped intracavity by a standard CPM dye laser. The desire for broad tunability, cw operation, and femtosecond pulses dictates the use of a thin crystal with a singly resonant cavity and, therefore, pumping with very high-peak intensities such as exist in a CPM cavity. This adds complexity, but results in a device which should be tunable over its complete phasematching bandwidth of 3.5 × 10¹⁴ Hz(720-4.5μm). This source provides ca. 100 fs pulses continuously at 10⁸ Hz and mW average powers, diffraction-limited beams, and 3% rms noise; thus it is highly suited to typical pump-probe type measurements in condensed matter. Data characterizing the performance will be presented along with brief mention of the theory, design, alignment, and evaluation of alternative possibilities. Our first experimental results using this source for tunable ultrafast measurements of hot carrier dynamics in InGaAs and other compound semiconductors will be presented. A very broad range of semiconductors, color centers, and molecular systems may be accessed with this laser for both ultrafast and cw measurements.

© 1990 Optical Society of America