Pump‐probe method for measurement of thickness of molten layer produced by ultrashort laser pulse

Pump‐probe technique provides an unique method for high precision measurement of ultrafast processes induced in material by ultrashort laser pulses. The time domain and space domain available for measurements are 0.1–1000 ps and 1–1000 nm, respectively. In this respect the pump‐probe technique noticeably extends to smaller scales the well‐known Doppler Velocity Interferometer System for Any Reflector (VISAR) and Optically Recording Velocity Interferometer System (ORVIS) methods, which have micron‐nanosecond accuracy. VISAR and ORVIS are widely used for study of wave dynamics in material plate having thickness from tens microns to several millimeters.

For the first time we apply pump‐probe technique for deep probing of ultrasonic melting of micron‐size aluminum film irradiated by ultrashort laser pump pulse. The pump with duration less than ∼1 ps may result in ultra‐high strain rate $V̇/V∼109–1010 s−1$ in such thin film. The experimental data and simulation analysis of material response and pressure wave dynamics are presented. The tensile strength of molten aluminum for different temperatures and strain rates was obtained.