Pulse duration effect on the distribution of energetic particles produced by intense femtosecond laser pulses irradiating solids

The energy distribution of hot electrons produced by a very short, intense laser pulse (I=2/4x10(18) W/cm(2), 60 fs, lambda =800 nm, obliquely inciden t p polarized) is investigated theoretically via particle simulation and ex perimentally via measurements of the electron distribution in the MeV regio n and the Doppler-shifted emission spectrum of fast ions. This energy distr ibution is shown to be greatly different from the known two-temperature dis tribution. The hot electrons with energies near the maximal (similar to2 Me V) constitute the distribution with an effective temperature T-h considerab ly higher than that of lower-energy electrons, which dominate the emission of energetic ions. The temperature scaling with the laser intensity differs from the known T(h)similar toI(1/2). (C) 2001 American Institute of Physic s.