Harmonic radiation emission from periodic lattices irradiated by short-pulse elliptically polarized laser light - art. no. 046604

Radiated emission at high-order harmonic numbers is observed from thin crys talline layers irradiated by short femtosecond elliptically polarized laser light. The applied external radiation field drives the free electrons in t he material to large oscillation amplitudes and harmonics are generated by the electronic response to the periodic lattice potential. A model was modi fied by introducing a more general expression for the lattice force that by sharpening or by smoothing the potential in turn allows the strength of th e electronic perturbation to be varied. The electron motion is computed num erically by solving the electromagnetic force equation and by regarding the lattice potential as a perturbative source. For linearly polarized laser l ight the radiation spectra are characterized by emission lines forming a fl at plateau in the region of low harmonic orders with a sharp cutoff for hig her numbers. For circular polarization strong emission is found for two har monic numbers, the first in the low-harmonic region and the second around t he cutoff. By solving analytically the electron motion in an elliptically p olarized laser field, an exact expression for the electron displacement in all three spatial directions is found. The amplitude of the oscillations se ts the analytic form for calculating the peak harmonic numbers emitted from the laser-lattice interaction. The radiation effect studied here, if detec ted, might hold some potential as a diagnostic and could be used, in princi ple, as a method for determining the lattice parameter in crystalline struc tures.