Delocalization of focused intense ultra-short laser pulses in air and transparent solids

Ti:Al₂O₃ lasers emitting pulses with duration τ = 100-140 fs at basic wavelength λ = 800 nm were used in most of the experiments. Gaussian laser beams were focused either in atmospheric air (helium, argon) or inside the bulk of silicon or diamond samples with approximately equal spot radius r_{b ≈}10-15um. In the case of silicon target by means of OPA λ was shifted to 1200 nm. Measurements of scattered light were performed calorimetrically. Variation of medium refractive index (Δn) was controlled by pump-probe setup combined with sensitive interferometer.