Transmittance jump in a thin aluminium layer during laser ablation

A jump in the transmittance (from ∼0.1% to ∼50% for ∼1 ns) of an optical gate on a Mylar film (a thin aluminium layer on a Lavsan substrate) irradiated by nanosecond (10^-7–10^-8 s) pulses of a neodymium laser with an intensity up to 0.1 GW cm^-2 has been recorded. The mechanism of a fast (10^-10–10^-11 s) increase in the transmittance of the aluminium layer upon its overheating (without boiling) to the metal – insulator phase-transition temperature is discussed.