Geometrical limitations in grating pair pulse compression.
Optical-pulse compression using gratings has become a standard technique for producing ultrafast pulses outside a laser cavity. Short pulses produced by a mode-locked laser are focused into an optical fiber. There, self-phase modulation and group velocity dispersion act to broaden the bandwidth of the pulse and impart to it a negative chirp. A pair of diffraction gratings are placed following the fiber. Different frequencies follow different paths through the grating pair; if they are properly oriented, the gratings can compensate for the linear chirp of the pulse. In this way the spectral components of the pulse are compressed in time. The net effect of the system is to produce an output pulse that is shorter than the input pulse because of the additional frequencies generated in the fiber.