  Direct compression of femtosecond optical pulses from a Ti:sapphire laser
oscillator was realized with a cholesteric liquid crystal acting as a nonlinear
1D periodic Bragg grating. With a 6-um thick sample, the pulse duration could
be compressed from 100 to 48 femtoseconds. Coupled-mode equations for forward
and backward waves were employed to simulate the dynamics therein and good
agreement between theory and experiment was obtained.
