DISPERSED FEMTOSECOND PULSES IN THE VICINITY OF FOCUS

Temporal and spatial intensity distribution of a femtosecond laser bea m having angular dispersion was studied in the focal plane of an achro matic lens. The appropriate diffraction integrals are calculated for s patially homogeneous pulses with square, Gaussian and secant hyperboli c temporal shapes. The temporal dependence of the illumination in the focus is shown to have parabolic shape independently of the input puls e shape. Physical explanation of this phenomenon is also presented.