Abstract

By sweeping the frequency of a diode laser beam near the cesium resonance frequency, followed by propagation through a short length of cesium vapor, we obtained periodic peaks with peak-to-average ratios near 5 at pulse repetition rates up to a gigahertz. Light in the wings of a strong atomic absorption line of an alkali metal vapor encounters large group velocity dispersion. A frequency modulation in an off-resonance cw beam passing through the vapor consequently develops an amplitude modulation. For certain combinations of laser and vapor parameters, a sinusoidally frequency modulated beam can be made to develop peaks. We generated pulse trains in a frequency modulated single mode diode laser tuned to the cesium absorption line near 852 nm, which we observed by using a fast p-i-n photodiode and a sampling oscilloscope. The frequency of a diode laser was sinusoidally modulated with a sweep of about a gigahertz and a period of a few nansoseconds by introducing a small modulation into the laser pump current. We observed the formation of sharp peaks with a width of about one-tenth of the modulation period and a peak-to-background ratio of approximately 5.

© 1992 Optical Society of America