  We propose to extend coherent laser cooling from narrow-band to broad-band
transitions by using trains of ultrashort broadband pulses. We study
analytically two possible methods to reduce the momentum spread of a
distribution by several units of photon momentum in a single spontaneous
emission lifetime. We report on numerical simulations of one-dimensional laser
cooling of a two-level system with realistic parameters. The technique
introduced here is of high interest for efficient laser cooling of fast species
with short lifetime such as positronium.
