Chiral effects appear in a wide variety of natural phenomena and are of fundamental importance in science, from particle physics to metamaterials. The standard technique of chiral ...discrimination—photoabsorption circular dichroism—relies on the magnetic properties of a chiral medium and yields an extremely weak chiral response. Here, we propose and demonstrate an orders of magnitude more sensitive type of circular dichroism in neutral molecules: photoexcitation circular dichroism. This technique does not rely on weak magnetic effects, but takes advantage of the coherent helical motion of bound electrons excited by ultrashort circularly polarized light. It results in an ultrafast chiral response and the efficient excitation of a macroscopic chiral density in an initially isotropic ensemble of randomly oriented chiral molecules. We probe this excitation using linearly polarized laser pulses, without the aid of further chiral interactions. Our time-resolved study of vibronic chiral dynamics opens a way to the efficient initiation, control and monitoring of chiral chemical change in neutral molecules at the level of electrons.
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. We implemented self-referenced attosecond photoelectron interferometry to measure the temporal profile of the forward and backward electron wave packets emitted upon photoionization of camphor by circularly polarized laser pulses. We measured a delay between electrons ejected forward and backward, which depends on the ejection angle and reaches 24 attoseconds. The asymmetric temporal shape of electron wave packets emitted through an autoionizing state further reveals the chiral character of strongly correlated electronic dynamics.
We performed angle-resolved photoemission spectroscopy (ARPES) of bulk 2HWSe2 for different crystal orientations linked to each other by time-reversal symmetry. We introduce a new observable called ...time-reversal dichroism in photoelectron angular distributions (TRDAD), which quantifies the modulation of the photoemission intensity upon effective time-reversal operation. We demonstrate that the hidden orbital pseudospin texture leaves its imprint on TRDAD, due to multiple orbital interference effects in photoemission. Our experimental results are in quantitative agreement with both the tight-binding model and state-of-the-art fully relativistic calculations performed using the one-step model of photoemission. While spin-resolved ARPES probes the spin component of entangled spin-orbital texture in multiorbital systems, we unambiguously demonstrate that TRDAD reveals its orbital pseudospin texture counterpart.
Photoionization of chiral molecules by circularly polarized radiation gives rise to a strong forward/backward asymmetry in the photoelectron angular distribution, referred to as photoelectron ...circular dichroism (PECD). Here we show that PECD is a universal effect that reveals the inherent chirality of the target in all ionization regimes: single photon, multiphoton, above-threshold and tunnel ionization. These different regimes provide complementary spectroscopic information at electronic and vibrational levels. The universality of the PECD can be understood in terms of a classical picture of the ionizing process, in which electron scattering on the chiral potential under the influence of a circularly polarized electric field results in a strong forward/backward asymmetry.
Performing ground-based submillimetre observations is a difficult task as the measurements are subject to absorption and emission from water vapour in the Earth's atmosphere and time variation in ...weather and instrument stability. Removing these features and other artefacts from the data is a vital process which affects the characteristics of the recovered astronomical structure we seek to study. In this paper, we explore two data reduction methods for data taken with the Submillimetre Common-User Bolometer Array-2 (SCUBA-2) at the James Clerk Maxwell Telescope (JCMT). The JCMT Legacy Reduction 1 (JCMT LR1) and The Gould Belt Legacy Survey Legacy Release 1 (GBS LR1) reduction both use the same software (starlink) but differ in their choice of data reduction parameters. We find that the JCMT LR1 reduction is suitable for determining whether or not compact emission is present in a given region and the GBS LR1 reduction is tuned in a robust way to uncover more extended emission, which better serves more in-depth physical analyses of star-forming regions. Using the GBS LR1 method, we find that compact sources are recovered well, even at a peak brightness of only three times the noise, whereas the reconstruction of larger objects requires much care when drawing boundaries around the expected astronomical signal in the data reduction process. Incorrect boundaries can lead to false structure identification or it can cause structure to be missed. In the JCMT LR1 reduction, the extent of the true structure of objects larger than a point source is never fully recovered.
Deep-sea hydrothermal vents are associated with seafloor tectonic and magmatic activity, and the communities living there are subject to disturbance. Eruptions can be frequent and catastrophic, ...raising questions about how these communities persist and maintain regional biodiversity. Prior studies of frequently disturbed vents have led to suggestions that faunal recovery can occur within 2-4 years. We use an unprecedented long-term (11-year) series of colonization data following a catastrophic 2006 seafloor eruption on the East Pacific Rise to show that faunal successional changes continue beyond a decade following the disturbance. Species composition at nine months post-eruption was conspicuously different than the pre-eruption 'baseline' state, which had been characterized in 1998 (85 months after disturbance by the previous 1991 eruption). By 96 months post-eruption, species composition was approaching the pre-eruption state, but continued to change up through to the end of our measurements at 135 months, indicating that the 'baseline' state was not a climax community. The strong variation observed in species composition across environmental gradients and successional stages highlights the importance of long-term, distributed sampling in order to understand the consequences of disturbance for maintenance of a diverse regional species pool. This perspective is critical for characterizing the resilience of vent species to both natural disturbance and human impacts such as deep-sea mining.
High-harmonic generation is typically thought of as a sub-laser-cycle process, with the electron’sexcursion in the continuum lasting a fraction of the optical cycle. However, it was recently ...suggested thatlong-lived Rydberg states can play a particularly important role in high harmonic generation by atomsdriven by the combination of the counterrotating circularly polarized fundamental light field and its secondharmonic. Here we report direct experimental evidence of very long and stable Rydberg trajectoriescontributing to high-harmonic generation in such fields. We track their dynamics inside the laser pulseusing the spin-orbit evolution in the ionic core, utilizing the spin-orbit Larmor clock. We confirm theireffect on harmonic emission both via microscopic simulations and by showing how this radiation can leadto a well-collimated macroscopic far-field signal. Our observations contrast sharply with the general viewthat long-lived Rydberg orbits should generate negligible contribution to the macroscopic far-field highharmonic response of the medium
We propose and implement a method to determine the absolute density profile of a gas jet producing high-order harmonics. By measuring the transverse profile of the fluorescence emitted by the plasma, ...we retrieve the local density in the gas jet. We use this technique during the optimization of the high-harmonics of 515 nm, 10 µJ, 130 fs pulses at 500 kHz and find that we can generate in absorption-limited conditions.
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