X-ray harmonic generation by orthogonally polarized two-color fields: Spectral shape and polarization

Abstract

Orthogonally polarized two-color fields, typically with a frequency ratio of 2:1, only rarely of 3:1, have been utilized for a variety of purposes. Driving high-order harmonic generation (HHG), the former yield linearly and the latter elliptically polarized harmonics. With emphasis on the 3:1 frequency ratio, we investigate the shape of the HHG spectrum for the fundamental frequency being in the midinfrared range (2200 nm). Depending on the relative phase between the two field components, a plethora of spectral shapes can be realized. For a suitable phase, the harmonic power can be concentrated within the highest 10% of the spectrum. The results are analyzed in terms of quantum orbits. For the 3:1 case, the scheme suggests an efficient table-top source of elliptically polarized soft x rays.