Interferometric circular dichroism in photoelectron momentum distributions

We study polarization effects in photoionization of achiral matter and report on two types of circular dichroism driven by a pair of time-delayed copropagating broadband pulses. Both being of interferometric nature, they manifest in the photoelectron momentum distribution (PMD) and vanish for fully time overlapping pulses having the same carrier-envelope phase. The first type, called atomic interferometric circular dichroism (AICD), is demonstrated in photoionization of the H atom or ${\mathrm{H}}_{2}$ aligned along the pulse propagation direction $\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{\mathbf{k}}\ensuremath{\parallel}\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{\mathbf{R}}$. It is shown to be directly visualized through mirroring effects from two key interferograms created in the PMD within two polarization schemes: (i) spiral patterns produced by a pair of counterrotating circularly polarized pulses and (ii) tuning-fork-like patterns driven by linearly and circularly polarized pulses. The second type is dubbed molecular interferometric circular dichroism (MICD) as it occurs in molecular photoionization within the configuration $\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{\mathbf{k}}\ensuremath{\perp}\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{\mathbf{R}}$. However, while the MICD occurs in polarization scheme (i), it is shown to interplay with the molecular-symmetry-mixed dichroism [Phys. Rev. Lett. 123, 143202 (2019)] in scheme (ii). Switching the helicities or ordering of the two pulses is shown to be consistent with time-reversal symmetry, except when $\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{\mathbf{k}}\ensuremath{\perp}\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{\mathbf{R}}$ in scheme (ii). Exhibiting an inversion symmetry, characteristic of unpolarized targets, the manifestation of the AICD and MICD in the PMD can serve as target chirality identification in life and chemical science. Our predictions based on nonstationary quantum-mechanical calculations are within the reach of current attosecond or femtosecond laser technology, making this study timely for experimental verification.