Lattice-parameter determination from the interaction of short femtosecond laser pulses with crystalline solids

A novel method for determining the lattice parameter in a crystalline solid from the harmonic emission spectra reflected in laser-solid layers interactions is proposed. Radiated emission at high-order harmonic numbers is observed from thin crystalline layers illuminated by short femtosecond elliptically polarized laser light. The radiation mechanism presented here accounts for optical emission effects when free electrons in the material, ionized by the action of an applied external radiation field, are driven to large oscillation amplitudes and harmonics are generated by the electronic response to the periodic lattice potential. Perturbations in the electron motion inside the material due to the ion cores give rise to harmonic emission. In this work, the condition for radiation--the resonance condition--is found analytically through an exact expression for the electron displacement. The analytic prediction is supported by results obtained by solving numerically the electromagnetic force equations for electrons moving in the lattice potential.