Temporal and thermodynamic characteristics of plasma formation

An investigation was made of plasma formation accompanying the interaction with aluminum, iron, and VK-6 alloy targets of nanosecond radiation from a YAG:Nd³⁺ laser (E_max = 50 mJ, τ = 3–8 ns). The duration of the plasma formation process depended weakly on the laser radiation parameters [the power density was varied in the range 1–3 GW/cm², the pulse rise time in the range 2–8 ns, or the rate of rise of the power density in the range (1–8) X 10⁸ W · cm ^{– 2} · ns ^–1]. A study was made of the establishment of a local thermodynamic equilibrium in a plasma jet excited by radiation from nanosecond and picosecond (E = 30 mJ, τ = 40 ps) lasers. The maximum of the luminescence from an aluminum plasma excited by picosecond laser radiation was found to correspond to a local thermodynamic equilibrium. A local thermodynamic equilibrium could be absent in the case of excitation by nanosecond laser radiation.