High Harmonic Generation and the Lorentz Drift

Benjamin Galloway, University of Colorado, Boulder

We present a semi-classical study of the effects of the Lorentz force on electrons during high harmonic generation driven by near- and mid-infrared lasers with wavelengths from 800 nm to 20 μm and at intensities ≈ 1015 W/cm2. The transverse extent of the longitudinal Lorentz drift is compared for both Gaussian focus and waveguide geometries. Both geometries exhibit a longitudinal electric field component that cancels the magnetic component of the Lorentz drift in some regions of the focus once each full optical cycle. We show that the Lorentz force contributes a super Gaussian scaling which acts in addition to the usual high harmonic flux scaling of λ-(5-6) due to quantum diffusion. We predict that the high harmonic yield will be reduced for driving wavelengths greater than 6 μm and that the presence of dynamic spatial mode asymmetries results in the generation of even harmonic orders – a peculiarity in this field. However, in contrast to previous work, we show that under realistic conditions with a focal spot of finite size, the recollision process does not shut off completely even for very long wavelengths and recollision energies greater than 15 keV.

Abstract Author(s): B. Galloway, D. Popmintchev, M.M. Murnane, H.C. Kapteyn, T. Popmintchev