Spatial distribution of carrier-envelope phase for femtosecond pulsed laser beam profile determined by asymmetric spectral interferometry.

The spatial distribution of the carrier-envelope phase (CEP) for a femtosecond laser pulse from a regenerative amplifier was measured by a method based on the spectral interferometric technique. Our results show that the spatial distribution of the carrier-envelope phase from an ultrafast regenerative amplified laser is stable from pulse to pulse, but the difference between different locations within the laser profile is significant. In contrast, the CEP spatial distribution for the beam profile from the oscillator is homogenous within the experimental error. We attribute the observed spatial CEP distribution to the discrepancy between the dispersion of group velocity and phase velocity when the laser pulse passes through the dispersive optical elements, which can be corrected by a prism.