LAUSR

The physical reason for the difference between the small-scale self-focusing of nanosecond and femtosecond pulses is that the typical intensity of the latter is three orders of magnitude higher, i.e., TW/cm2 versus GW/cm2. This causes a significant shift of the growth-rate maximum of the Bespalov–Talanov instability to the region of high spatial frequencies. During free propagation, a decrease in the spectral density of noise and the self-filtering of the beam lead to the noise-density decrease in the region of the maximum growth rate and, therefore, slowing of the self-focusing development. This is shown to shift the restriction on using the transmissive optical elements in the superpower lasers towards high powers.