Two different pulse compressors for relatively intense optical beams differ from the prior art both in employing a two-photon dispersion effect and in employing a different set of modulations than is conventional for "chirped" pulse compressors. The first one depends upon turning on and then turning off a two-photon dispersion effect of an atomic gaseous medium upon a first coherent beam from which the pulse is to be formed. The effect is turned on and off by the second beam within a time period not substantially more than the length of the medium divided by the dispersive group velocity of the first beam in the medium. The dispersion in effect allows energy to be concentrated in the medium by means of a temporary delay. The second device is analogous to that of U.S. Pat. No. 3,679,313 to R. L. Rosenberg, issued July 25, 1972, in employing overlapping "comb" patterns of modulation products but differs therefrom in that it replaces the dispersive interferometer with the two-photon dispersive gas medium and employs much wider frequency modulations. The first beam is chirped, or frequency-modulated, at a first rate; but the second beam is frequency-modulated at a rate sufficiently different from that of the first beam that the modulation product combs intermesh to provide two-photon interaction over the broadest possible frequency band.