Energy distribution of electrons ejected from a copper target in a femtosecond laser field of 1017 W/cm2

The energy distribution of electrons ejected from laser-induced plasma was measured using a magnetic spectrometer. The spectrometer was developed for quantitative analysis using an imaging plate. The efficiency of the imaging plate for detecting energetic electrons was calibrated using a transmission electron microscope, which accelerates electrons into energies between 80 and 200 keV. The kinetic energy distribution of electrons, which are ejected towards the backward direction, was measured on a copper bulk target irradiated with an infrared 60 fs laser. The obtained effective electron temperature in the energy range between 60 and 200 keV corresponded to approximately 130 keV at an intensity of 3.3x10(17) W/cm(2). This temperature was consistent with a scaling of 100[Ilambda(2)/10(17) (W mum(2)/cm(2))](1/3) keV by Beg [Phys. Plasma 4, 447 (1997)] derived from resonance absorption. (C) 2004 American Institute of Physics.