DIRECT MEASUREMENT OF THE SPECTRAL PHASE OF FEMTOSECOND PULSES

We measure the spectral phase of femtosecond optical pulses using a ti me-frequency analog of Young's double-slit interference. A pair of nar row slits in an opaque sheet selects two spectral frequencies from the femtosecond pulse spectrum in a zero-dispersion pulse stretcher. Meas urement of the temporal phase of a family of beat frequencies obtained over a range of slit spacings yields the desired spectral phase direc tly. We demonstrate this technique by accurately measuring the quadrat ic phase added to 80-fs optical pulses by a 6.5-cm block of BK-7 glass .