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Journal of Physics B: Atomic, Molecular and Optical Physics - latest papers
Latest articles for Journal of Physics B: Atomic, Molecular and Optical Physics
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Coenhancement of optical transmission and Faraday effect with magnetic plasmonic nanopillars
Coenhancement of optical transmission and the Faraday effect are always the goals to pursue for photoelectric devices, while the current research almost concentrated on the properties based on gratings and photonic crystal structures. Nanopillars (NPs) are structures with a relatively simple preparation that have been widely used in many fields, where the Faraday effect has been rarely studied. In this work, a Faraday rotator in the wavelength range of 500–800 nm is proposed based on bismuth–iron garnet (BIG) with magnetic plasmonic NPs structure, in which the hemispherical shaped silver covered on top and silica used as the substrate for enhancement effect. Through this rotator, two peak values for both Faraday rotation angle and transmittance can be achieved, no matter what the wavelength changes are. The transmittance, Faraday rotation angle, and figure of merit (FOM) can be controlled by tuning the thickness and lattice constant of the BIG NPs, the radius of the silver hemisphere, and the external magnetic field. Furthermore, the physics mechanism of the large Faraday effect and extraordinary optical transmission is explained by employing the electric field distribution diagrams. Finally, the optimized FOM simply can be raised to 0.9, achieving well overall performance in the visible light range. The results have certain values for achieving simpler and better performance of magneto-optical devices under visible wavelength range, such as optical isolators and magneto-optical sensors.
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Competing excitation quenching and charge exchange in ultracold Li-Ba+ collisions
Hybrid atom-ion systems are a rich and powerful platform for studying chemical reactions, as they feature both excellent control over the electronic state preparation and readout as well as a versatile tunability over the scattering energy, ranging from the few-partial wave regime to the quantum regime. In this work, we make use of these excellent control knobs, and present a joint experimental and theoretical study of the collisions of a single 138Ba+ ion prepared in the metastable states with a ground state 6Li gas near quantum degeneracy. We show that in contrast to previously reported atom-ion mixtures, several non-radiative processes, including charge exchange, excitation exchange and quenching, compete with each other due to the inherent complexity of the ion-atom molecular structure. We present a full quantum model based on high-level electronic structure calculations involving spin-orbit couplings. Results are in excellent agreement with observations, highlighting the strong coupling between the internal angular momenta and the mechanical rotation of the colliding pair, which is relevant in any other hybrid system composed of an alkali-metal atom and an alkaline-earth ion.
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Fine-structure changing collisions in 87Rb upon D2 excitation in the hyperfine Paschen-Back regime
We investigate fine structure changing collisions in 87Rb vapour upon D2 excitation in a thermal vapour at 75 ∘C; the atoms are placed in a 0.6 T axial magnetic field in order to gain access to the hyperfine Pashen-Back regime. Following optical excitation on the D2 line, the exothermic transfer 5P 5P occurs as a consequence of buffer-gas collisions; the 87Rb subsequently emits a photon on the D1 transition. We employ single-photon counting apparatus to monitor the D1 fluorescence, with an etalon filter to provide high spectral resolution. By studying the D1 fluorescence when the D2 excitation laser is scanned, we see that during the collisional transfer process the quantum number of the atom changes, but the nuclear spin projection quantum number, , is conserved. A simple kinematic model incorporating a coefficient of restitution in the collision accounted for the change in velocity distribution of atoms undergoing collisions, and the resulting fluorescence lineshape. The experiment is conducted with a nominally ‘buffer-gas free’ vapour cell; our results show that fine structure changing collisions are important with such media, and point out possible implications for quantum-optics experiments in thermal vapours producing entangled photon pairs with the double ladder configuration, and solar physics magneto-optical filters.
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XFEL SASE pulses can enhance time-dependent observables
X-ray free electron lasers (XFELs) have emerged as powerful sources of short and intense x-ray pulses. We propose a simple and robust procedure which takes advantage of the inherent stochasticity of self-amplified stimulated emission (SASE) pulses to enhance the time-resolution and signal strength of the recorded data. Notably, the proposed method is able to enhance the average signal without knowledge of the signal strength of individual shots. Simple metrics for the probe pulses are introduced, such as an effective pulse duration applicable to SASE pulses characterised in the time domain using e.g. an X-band transverse cavity. The approach is evaluated using simulated and real pulse data in the context of ultrafast electron dynamics in a molecule. Utilising H2 as a model system, we demonstrate the efficacy of the method theoretically, successfully enhancing the predicted nonresonant ultrafast x-ray scattering signal associated with electron dynamics. The method presented is broadly applicable and offers a general strategy for enhancing time-dependent observables at XFELs.
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Nanoplasma formation and expansion ignited by an intense FEL: a study using pump-probe electron spectroscopy
We demonstrate real-time observations of nanoplasma formation and expansion using intense extreme-ultraviolet (XUV) and near-infrared (NIR) pump–probe electron spectroscopy. We identified the formation of a nanoplasma by the sudden enhancement of low-energy electron emission within a few tens of femtoseconds after XUV excitation, which indicates considerable heating of the clusters by the NIR field. We probed the subsequent expansion of the nanoplasma by monitoring the transient resonant enhancement of high-energy electron emission. The dependence of the resonance on the XUV intensity is explained by the expansion speed of the XUV-induced nanoplasma.