An adaptive pulse compressor is described, especially for use with ultrashort pulses, wherein the input pulses are modified in an iterative fashion, according to a feedback signal obtained from measurement of the output pulses. The feedback signal is programmed, by means of a programmable spatial light modulator, to allow for independent control of the individual spectral components of the incoming pulses, such that almost arbitrary phase functions can be realized to accomplish efficient compression. One of the main disadvantages associated with prior art pulse compressors, namely, the need for characterization of the uncompressed pulses, is thus eliminated. The compressor is thus capable of handling completely uncharacterized or partially characterized input pulses, or pulses from time varying sources.