LAUSR

Abstract The experimental and theoretical investigations of attosecond pulses diffraction describe one unexpected parabolic deformation of their intensity profile at few diffraction lengths. This deformation was called by some authors λ3 diffraction. In our previous works it was shown that this phenomenon can be solved analytically in the frame of linear non-paraxial evolution equation of the amplitude of the electrical field. In addition, by solving numerically this equation for phase-modulated femtosecond pulses (20–30 fs) we demonstrated that broad-band pulses also diffract in λ3 regime. Shortly, Fresnel's law does not work for broad-band laser pulses and their diffraction is similar to attosecond ones. On the other hand, by using diffraction grating or other optical dispersion elements the spectrum of the femtosecond pulse can be not only extended, but also the sign of the chirp parameter can be changed. In the present work, it is studied more precisely the influence of the sign and value of the chirp parameter on the linear evolution of phase-modulated femtosecond pulses.