Focusability of a femtosecond laser pulse after the Treacy compressor with diffraction gratings with small-scale and large-scale non-flatness.

Analytical expressions for the focal intensity (Strehl ratio) were obtained for both small-scale and large-scale variations in the surface profile of the compressor diffraction grating substrate. The validity of the expressions is confirmed by numerical simulations. It is shown that for small (much less than the beam diameter)-scale variations with rms of less than 10 nm of their influence can be neglected. Numerical simulations confirmed that quadratic aberrations (defocus and astigmatism) can be suppressed by rotating the fourth grating; and therefore, grating manufacturers should ignore these aberrations to minimize higher orders.