Abstract

An apparatus for doing picosecond, narrowband infrared spectroscopy is presented. The procedure, based on a 540 Hz regenerative amplifier, uses a gated up-conversion technique. Spectral resolution of 1 cm⁻¹ is achieved by difference-frequency mixing the output of a narrowband, sync-pumped, grating dye laser, which is pumped by residual light from the regenerative amplifier, with 532 nm laser light in LiI0₃. The output is narrowband infrared with a relatively high intensity compared to a cw source and is easily tunable over 500 cm⁻¹ around 5 u. Time resolution of ps is achieved by a gated up-conversion technique. We plan to improve our resolution to fs by compressing out the laser light used for gating. The high repetition rate of the regenerative amplifier, in concert with synchronized phase-sensitive detection, provide outstanding signal-to-noise values. Detection of pump-induced transmission changes of the probe pulse of less than one part in a thousand has been demonstrated. This sensitivity is needed to do transient, vibrational spectroscopy where the typical ratio of vibrational cross-sections to electronic cross-sections is about 10⁻³. We have applied our system to experiments on ligand dissociation of CO from carboxymyoglobin.

© 1990 Optical Society of America