Abstract

Frequency-modulation spectroscopy is among the best techniques for sensitive absorption measurements with cw lasers, but its extension to pulsed lasers has been problematic. Some years ago, Gallagher and coworkers used very large FM sideband offsets, typically 10–20 GHz, to obtain FM spectra by using a multimode dye laser.¹ We report an improved approach, using pulsed amplification to produce transform- limited, temporally smooth pulses that are especially well suited for FM spectroscopy and other techniques requiring a well-defined optical phase. This approach offers much higher spectral resolution, a better- defined optical phase, and a much smaller modulation frequency that allows more sensitive and flexible detection. We are also exploring new methods for digital signal processing that will extend the capabilities of conventional arrangements using balanced mixers.

© 1995 Optical Society of America