  We quantify the dependence of the single-shot ablation threshold on the angle
of incidence and polarization of a femtosecond laser beam, for three dissimilar
solid-state materials: a metal, a dielectric and a semiconductor. Using the
constant, linear value of the index of refraction, we calculate the laser
fluence transmitted through the air-material interface at the point of ablation
threshold. We show that, in spite of the highly nonlinear ionization dynamics
involved in the ablation process, the so defined transmitted threshold fluence
is universally independent of the angle of incidence and polarization of the
laser beam for all three material types. We suggest that angular dependence of
ablation threshold can be utilized for profiling fluence distributions in
ultra-intense femtosecond laser beams.
