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Circularly polarized high-harmonic generation with a bicircular laser field

Focus

The standard experimental configuration for high-harmonic generation (HHG) -- the highly nonlinear process by which a gas of atoms or molecules irradiated by a strong laser pulse emits an electromagnetic radiation composed of integer multiples of the driving field -- consists of a linearly polarized source. Yet, with the progresses in laser technologies and advances in our understanding of such strong laser-matter interactions, it was soon realized that alternative polarizations/laser configurations could be used as means to probe and control the physical processes at play. In this perspective, here we investigate the question of high-harmonic generation with a bicircular laser pulse, i.e., composed of two circularly polarized color components. Applied to molecular systems, instead of the standard electric dipole selection rules, which cannot be invoked because of the absence of angular momentum conservation for the field-free dynamics, we show that spectral properties are connected to discrete dynamical symmetries. Compared with numerical simulations, we show that molecular systems offer a robust framework for circularly polarized harmonics, which orders and helicities (left or right polarized) are accurately predicted with our theory.

Associated publications

Circularly polarized harmonic generation by intense bicircular laser pulses: electron recollision dynamics and frequency dependent helicity

posted Nov 14, 2016, 8:51 AM by François Mauger   [ updated Nov 14, 2016, 8:51 AM ]

Abstract

Numerical solutions of time-dependent Schrödinger equations for one and two electron cyclic molecules Hnq+ exposed to intense bichromatic circularly polarized laser pulses of frequencies ω1 and ω2, such that ω12=n1/n2 (integer) produce circularly polarized high order harmonics with a cut-off recollision maximum energy at and greater than the linear polarization law (in atomic units) Nmω1=Ip+3.17Up, where Ip is the ionization potential and Up=(2E0)2/4ω2 is the ponderomotive energy defined by the field E0 (intensity I=cE02/8π) from each pulse and mean frequency ω=(ω12)/2. An electron recollision model in a rotating frame at rotating frequency Δω=(ω12)/2 predicts this simple result as a result of recollision dynamics in a combination of bichromatic circularly polarized pulses. The harmonic helicities and their intensities are shown to depend on compatible symmetries of the net pulse electric fields with that of the molecules.

Reference

A. Bandrauk, F. Mauger and KJ Yuan – Circularly polarized harmonic generation by intense bicircular laser pulses: Electron recollision dynamics and frequency dependent helicity –  Journal of Physics B: Atomic, Molecular and Optical Physics 49, 23LT01 (2016)

Circularly polarized molecular high harmonic generation using a bicircular laser

posted May 13, 2016, 10:40 PM by François Mauger   [ updated May 13, 2016, 11:09 PM ]

Abstract

We investigate the process of circularly polarized high harmonic generation in molecules using a bicircular laser field. In this context, we show that molecules offer a very robust framework for the production of circularly polarized harmonics, provided their symmetry is compatible with that of the laser field. Using a discrete time-dependent symmetry analysis, we show how all the features (harmonic order and polarization) of spectra can be explained and predicted. The symmetry analysis is generic and can easily be applied to other target and/or field configurations.

Reference

F. Mauger, A.D. Bandrauk, and T. Uzer - Circularly polarized molecular high harmonic generation using a bicircular laser - Journal of Physics B: Atomic, Molecular and Optical Physics 49, 10LT01 (2016)

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