Interference microscopy study of the preplasma formed on an iron target surface exposed to high-power femtosecond laser pulses

The characteristic scale of spread of the plasma formed on the surface of a bulk iron target irradiated by a femtosecond laser pulse with an intensity of 10¹⁶ W cm^-2 is measured by timeresolved interference microscopy using femtosecond pulses emitted by a Cr : forsterite laser system with an intensity contrast of 10⁷. The chosen technique is demonstrated to be efficient in such measurements. It is shown experimentally that, as a result of laser pulse impact, the displacement of a plasma layer with a density exceeding critical does not exceed 30 nm.