Subpicosecond transient excitation of atomic vapor and the measurement of optical phase

The transient behavior of a frequency-swept optical pulse transmitted through a resonant vapor cell is observed by an optical sampling technique with ˜20-fsec time resolution. The observed 200-fsec transients are the fastest intensity sampling measurement ever made on an atomic vapor and provide a precise determination of the time- varying phase of the pulse. The observed phase shows deviations from a linear frequency sweep, which may account for previous limits on pulse compression. © 1986 Optical Society of America.