HIGH-ORDER HARMONIC RADIATION FROM SOLID LAYERS IRRADIATED BY SUBPICOSECOND LASER-PULSES

High-order harmonic radiation from a thin solid layer illuminated by a subpicosecond laser pulse is investigated. For laser intensities I(L) and wavelengths lambda(L) with I(L)lambda(L)2 > 10(4) W mum2/cm2, free electrons oscillate with amplitudes delta extending over many lattice periods 1, of the solid and, due to interaction with the lattice, radiate a spectrum of harmonics with a sharp cutoff at n(max) congruent-to 2pidelta/l(c). Laser pulses (of order 100 fs) shorter than the lattice disintegration time are required. The harmonics emission crucially depends on electron correlations. Competing spontaneous atomic radiation is discussed.