High-order harmonic radiation from solid layers irradiated by subpicosecond laser pulses.

Abstract

High-order harmonic radiation from a thin solid layer illuminated by a subpicosecond laser pulse is investigated. For laser intensities ${\mathit{I}}_{\mathit{L}}$ and wavelengths ${\ensuremath{\lambda}}_{\mathit{L}}$ with ${\mathit{I}}_{\mathit{L}}$${\ensuremath{\lambda}}_{\mathit{L}}^{2}$>${10}^{14}$ W \ensuremath{\mu}${\mathrm{m}}^{2}$/${\mathrm{cm}}^{2}$, free electrons oscillate with amplitudes \ensuremath{\delta} extending over many lattice periods ${\mathit{l}}_{\mathit{c}}$ of the solid and, due to interaction with the lattice, radiate a spectrum of harmonics with a sharp cutoff at ${\mathit{n}}_{\mathrm{max}}$\ensuremath{\simeq}2\ensuremath{\pi}\ensuremath{\delta}/${\mathit{l}}_{\mathit{c}}$. 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.