Numerical simulation of harmonic generation by relativistic laser interaction with a grating.

The interaction of a femtosecond relativistic intensity laser pulse with a grating of subwavelength periodicity was simulated numerically. Strong coherent emission at the wavelength of the grating period and its harmonics was seen, nearly parallel to the target surface, due to relativistic electron bunches emanating from each protuberance. Normal and oblique incidence (30 degrees ) gave rise to trains of attosecond pulses and an efficiency greater than 10;{-4} was obtained for the 24;{th} harmonic (lambda approximately 16.7 nm) . Similarity theory gives optimum conditions for harmonic emission.