Response of a two-level atom to a frequency-modulated optically coherent pulse train

We present an analytical expression for the response of a two-level atom to a frequency-modulated optically coherent pulse train. The optical beam has sinusoidal frequency modulation and its chopped to have a square-wave envelope. We assume that the laser pulse are short compared with the atomic-decay time, the pulse-repetition time, and the modulation period. With this short-pulse assumption we are able to use a method similar to Temkin's [J. Opt. Soc. Am. B 10, 830-839 (1993)] and solve the optical Bloch equations in closed form.