Spin conservation in high-order-harmonic generation using bicircular fields

Abstract

We present an alternative theoretical model for a recent experiment [A. Fleischer et al., Nature Photon. 8, 543 (2014)] which used bichromatic, counter-rotating high intensity laser pulses to probe the conservation of spin angular momentum in high harmonic generation. We separate elliptical polarizations into independent circular fields with definite angular momentum, instead of using the expectation value of spin for each photon in the conservation equation, and we find good agreement with the experimental results. In our description the generation of each individual harmonic conserves spin angular momentum, in contrast to the model proposed by Fleischer et al. Our model also correctly describes analogous processes in standard perturbative optics. * e.pisanty11@imperial.ac.uk

Bicircular High-Harmonic Spectroscopy Reveals Dynamical Symmetries of Atoms and Molecules

“…When acting on an isotropic medium, the dynamical symmetry of the electric field translates into the emission of a comb of harmonics from which every third one, with frequency 3qω, is missing. The explanation of these selection rules has recently attracted considerable interest [23,[25][26][27]. We demonstrate that this property induces sensitivity to symmetry at two levels-the single-particle and the ensemble level.…”

Helicity reversion in high-order-harmonic generation driven by bichromatic counter-rotating circularly polarized laser fields

“…When the BCCP laser pulse is acting on an isotropic medium, in the frequency domain, a comb of high efficiency harmonic with frequency (3n±1)ω is radiated [7,[27][28][29]. According to the selection rules [26,[30][31][32][33], the harmonics with frequency (3n+1)ω have the same helicity as the fundamental while the (3n-1)ω harmonics have the same helicity as the second harmonic pulse (3nω is parity forbidden). Selecting harmonics with one kind of helicity would generate attosecond pulses with circular polarization.…”

Taking control of polarization

“…The channel (2; 1) is still allowed for the elliptically polarized blue driver -only its intensity is lower because there are fewer right-circularly polarized photons available for the process. Similar arguments apply to the higherorder processes [9].…”