Increase in the temperature of a laser plasma formed by two-frequency UV — IR irradiation of metal targets

An experimental investigation was made of a laser plasma formed by successive irradiation of a metal target with 30-ps UV and IR laser pulses. The UV prepulse, of 266 nm wavelength, was of relatively low intensity (~10¹² W cm^–2), whereas the intensity of an IR pulse, of 10.6 μm wavelength, was considerably higher (~3 × 10¹⁴ W cm^–2) and it was delayed by 0 — 6 ns (the optimal delay was 2 ns). Such two-frequency UV — IR irradiation produced a laser plasma with an electron temperature 5 times higher than that of a plasma created by singe-frequency IR pulses of the same (~3 × 10¹⁴ W cm^–2) intensity.