Attosecond-resolved photoionization of chiral molecules (2004.05010v1)

Abstract: Chiral light-matter interactions have been investigated for two centuries, leading to the discovery of many chiroptical processes used for discrimination of enantiomers. Whereas most chiroptical effects result from a response of bound electrons, photoionization can produce much stronger chiral signals that manifest as asymmetries in the angular distribution of the photoelectrons along the light propagation axis. Here we implement a self-referenced attosecond photoelectron interferometry to measure the temporal profile of the forward and backward electron wavepackets emitted upon photoionization of camphor by circularly polarized laser pulses. We found a delay between electrons ejected forward and backward, which depends on the ejection angle and reaches 24 attoseconds. The asymmetric temporal shape of electron wavepackets emitted through an autoionizing state further reveals the chiral character of strongly-correlated electronic dynamics.

Attosecond-Resolved Photoionization of Chiral Molecules

This paper presents a comprehensive paper on the ultrafast photoionization dynamics of chiral molecules, specifically focusing on the temporal resolution achieved through attosecond photoelectron interferometry. Chiral molecules exhibit interesting light-interaction properties, where the asymmetry in electron emission can be probed using photoelectron circular dichroism (PECD). The authors implement a self-referenced technique using circularly polarized laser pulses on camphor, a chiral molecule, to measure the temporal delay between electron wavepackets emitted forward and backward during photoionization.

Key Findings

1. Attosecond Delay Measurement: The experiment reveals delays reaching up to 24 attoseconds between forward and backward emitted electrons, influenced by ejection angles and indicative of chiral character in electron dynamics through an autoionizing state. This delay was previously elusive due to the technological limitations in measuring ultrafast electron dynamics.
2. Photoelectron Interferometry: Utilizing two phase-locked laser fields allows the separation of measurement-induced effects from intrinsic molecular delays. This method facilitates the accurate assessment of differential attosecond photoionization delays with a precision of 2 attoseconds, by controlling light pulse chirality.
3. Theoretical Implications: The PECD signals, which emerge due to electron scattering influenced by the molecular chiral potential, can be two orders of magnitude stronger than conventional chiroptical effects. These results provide insights into the underlying processes of enantio-specific ionization dynamics.
4. Differential Wigner Delays: The paper reveals the existence of asymmetric Wigner delays in the photoionization, even in randomly oriented samples, thus highlighting subtle features such as differential Cooper minima which survive the averaging effects over molecular orientation.
5. Resonant Photoionization Dynamics: A detailed exploration of dynamics in the presence of autoionizing resonances is conducted. The interference of direct and indirect ionization pathways results in unique quantum mechanical signatures, showing strong asymmetric electron wavepackets.
6. Self-Referenced Delay Decoupling: By controlling chirality of ionizing and probe pulses separately, the authors efficiently decouple intrinsic photoionization delays from measurement-induced delays, providing a more accurate depiction of the electron emission time.

Implications

The implications of this research are manifold. Practically, the findings contribute to developing advanced spectroscopic techniques for studying chiral molecules, relevant in fields such as pharmaceuticals and biochemical sensing. Theoretically, the detailed investigation of asymmetric electron dynamics presents benchmarks for quantum theories of molecular photoionization, pushing the boundaries of our understanding of multielectron dynamics and offering new perspectives for control schemes in quantum systems.

Future Directions

This work opens avenues for further exploration in various molecular systems beyond camphor, extending to other chiral complexes and potentially larger biomolecules. The demonstrated ability to resolve ultrafast electron dynamics and the subtle effects of molecular orientation suggest future developments could include more refined techniques for orientation-specific photoelectron measurements. Moreover, the exploration of ultrafast symmetry breakings presents potential applications in technological innovations involving chiral materials, such as chiral spintronics and superconducting devices.

The research underscores the advancements in attosecond photoelectron spectroscopy and its potential to revolutionize the paper of chiral molecules, enhancing our understanding of fundamental light-matter interactions.