Abstract
We derive here a new highly selective photoelectron-based chirality-sensing technique that utilizes 'locally-chiral' laser pulses. We show that this approach results in strong chiral discrimination, where the standard forwards/backwards asymmetry of photoelectron circular dichroism (PECD) is lifted. The resulting dichroism is much larger and more robust than conventional PECD, is found in all hemispheres, and is not symmetric or antisymmetric with respect to any symmetry operator. Remarkably, a CD of up to 10% survives in the angularly-integrated above-threshold ionization (ATI) spectra, and of up to 5% in the total ionization rates. We demonstrate these results through ab-initio calculations in the chiral molecules Bromochlorofluoromethane, Limonene, Fenchone, and Camphor. We also explore the parameter-space of the locally-chiral field and show that the observed CD is strongly correlated to the degree of chirality of the light, validating it as a measure for chiral-interaction strengths. Our results pave the way for highly selective probing of ultrafast chirality in ATI, can potentially lead to all-optical enantio-separation, and motivate the use of locally-chiral light for enhancing ultrafast spectroscopies.
Highlights
We derive here a highly selective photoelectron-based chirality-sensing technique that utilizes “locally chiral” laser pulses. We show that this approach results in strong chiral discrimination, where the standard forwards/backwards asymmetry of photoelectron circular dichroism (PECD) is lifted
Such a dichroism is obtained by subtracting the orientation-averaged photoelectron spectrum (PES) calculated from both enantiomers that interact with the same circularly polarized light (CPL), and integrating along one axis (which experimentally occurs in velocity map imaging (VMI) [6]): PECD(kx, kz )
We have reformulated the method of PECD to the use of noncollinear and bichromatic laser pulses that are locally chiral [30,40]
Summary
Dichroism arises in all hemispheres (i.e., forwards/backwards, up/down, left/right), and it is not purely symmetric or antisymmetric; that is, the resulting photoemission is in itself a chiral object This fundamental aspect leads to chiral dichroism of up to 10% that survives angular integration in ATI spectra, and up to 5% in the total ionization rates. In order to put our scheme into perspective, we first reformulate the main physical observable of PECD, which is a chiral dichroism observed in the angularly resolved PES from mirror-image enantiomers Such a dichroism is obtained by subtracting the orientation-averaged PES calculated from both enantiomers that interact with the same CPL, and integrating along one axis (which experimentally occurs in velocity map imaging (VMI) [6]): PECD(kx, kz ). By integrating over the energy in Eq (5) we obtain the discrimination in total photoelectron yield: IXD
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