High-order harmonic generation (HHG) is a nonlinear process that converts intense radiation, typically in the infrared domain, into high-frequency light [1]. It can be understood as a sequence of three steps: (1) tunnel ionization induced by the strong field, (2) laser-driven acceleration of the electron in the continuum, and (3) recombination with the parent ion, resulting in the emission of harmonic radiation [2]. Since there is a well-defined relationship between the duration of the electron round-trip and the energy released upon recombination, the harmonic spectrum records a movie of the dynamics induced in the ion [3].<br/><br/>Imaging sub-femtosecond chiral dynamics is a recent achievement of HHG spectroscopy [4-6]. The first implementation of chiral HHG (cHHG) exploited the chirality of elliptically polarized light for probing ultrafast chiral dynamics in propylene oxide and fenchone [4]. One could expect that increasing the ellipticity of the driving field would enhance the chiral response of the system. However, as the polarization is modified from linear to circular, the electron round-trip deviates from a straight line and thus the electron misses recombination with the core. This difficulty can be overcome by using bi-elliptical driving fields [5-7].<br/><br/>In this symposium, I will present our theoretical work on cHHG. First, I will show that bi-elliptical light can induce strong chiral response in the harmonic spectra of chiral molecules in a broad range of harmonic numbers and ellipticities [5,6], thus enabling ultrafast imaging of chiral dynamics at the level of electrons. Our calculations include accurate photo-recomination matrix elements, evaluated in the framework of density functional theory [8], and full coherent orientational averaging. I will also discuss how one can control and enhance the chiral response in cHHG by tailoring the driving field, in particular by tuning its frequency, intensity and ellipticity, showing that cHHG is a promising technique for chiral recognition, chiral discrimination and ultrafast imaging of chiral dynamics.

High harmonic generation in chiral media: from chiral discrimination to ultrafast imaging of molecular chirality

256th National Meeting (2018)

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