Origin and implication of ellipticity in high-order harmonic generation from aligned molecules

Abstract

We address theoretically and numerically the possibility of observing ellipticity in high-order harmonic generation (HHG) from aligned molecules driven by linearly polarized fields-a subject of controversy in the recent literature with significant implications. To that end we develop a numerical method for solution of the electronic dynamics and extend a recently developed theory of HHG from aligned molecules. Our numerical results are in good agreement with recent experimental data. The theory explains analytically several observations of polarization experiments. We note the conditions under which ellipticity can be observed and the information content of elliptically polarized harmonics regarding the molecular system.

Ellipticity of odd-even harmonics from oriented asymmetric molecules in strong linearly polarized laser fields

“…HHG can be well described by a three-step model [3,4] and has been shown to have promising applications in attosecond physics [5,6] and ultrafast imaging of molecular orbitals [7][8][9], Previous studies on HHG mainly focus on the power spectra of the harmonics emitted along the laser polarization (i.e., the parallel harmonics). Recently, great attention has been paid to the polarization of harmonics from aligned symmetric molecules, such as H2 + [10] and N2 [11][12][13][14]. Experimental and theoretical studies show that the elliptical polarization state of harmonics can be generated from aligned molecules irradiated by a linearly polarized laser field.…”

“…Experimental and theoretical studies show that the elliptical polarization state of harmonics can be generated from aligned molecules irradiated by a linearly polarized laser field. The possible origin of the ellipticity of HHG has been attributed to the multielectron effect [11], the Coulomb effect [13,14], twocenter interference [10], and quantum-mechanical uncertainty of the electron motion [15], As this polarization of HHG is closely related to not only the parallel harmonics and the harmonics emitted perpendicular to the laser polarization (i.e., the perpendicular harmonics) but also the phase of the harmonics, it provides other deep insights into the mechanism of the molecular HHG [16].…”

Probing the origin of elliptical high-order harmonic generation from aligned molecules in linearly polarized laser fields

“…Controversially, a theory including multiple electronic continuum dynamics predicts elliptical HHG from aligned CO 2 [15]. In general, according to the selection rules [16], elliptical harmonic radiation is expected unless the molecular alignment is parallel or perpendicular to the driving laser polarization. The widely used strong-field approximation (SFA), however, cannot predict this ellipticity of HHG at all because only the parallel component Since the mechanism of the elliptical HHG is still under debate and largely unknown, it is most desirable and timely to perform a fully ab initio study to explore and clarify the origin of the ellipticity.…”

Observation of the field-free orientation of a symmetric-top molecule by terahertz laser pulses at high temperature

“…Such phenomena play also a role in quantum computing [11] and high-order harmonic generation [12,13,14,15]. In this setting, molecular alignment and orientation can be identified as crucial prerequisites before exploring more complex control scenarios [16,4].…”