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Generalized perspective on chiral measurements without magnetic interactions
摘要： We present a unified description of several methods of chiral discrimination based exclusively on electric-dipole interactions. It includes photoelectron circular dichroism (PECD), enantiosensitive microwave spectroscopy (EMWS), photoexcitation circular dichroism (PXCD), and photoelectron-photoexcitation circular dichroism (PXECD). We show that, in spite of the fact that the physics underlying the appearance of a chiral response is very different in all these methods, the enantiosensitive and dichroic observable in all cases has a unique form. It is a polar vector given by the product of (i) a molecular pseudoscalar and (ii) a field pseudovector specified by the configuration of the electric fields interacting with the isotropic ensemble of chiral molecules. The molecular pseudoscalar is a rotationally invariant property, which is composed from different molecule-specific vectors and in the simplest case is a triple product of such vectors. The key property that enables the chiral response is the noncoplanarity of the vectors forming such triple product. The key property that enables chiral detection without relying on the chirality of the electromagnetic fields is the vectorial nature of the enantiosensitive observable. Our compact and general expression for this observable shows what ultimately determines the efficiency of the chiral signal and if, or when, it can reach 100%. We also discuss the differences between the two phenomena, which rely on the bound states, PXCD and EMWS, and the two phenomena using the continuum states, PECD and PXECD. Finally, we extend these methods to arbitrary polarizations of the electric fields used to induce and probe the chiral response.
关键词： photoelectron-photoexcitation circular dichroism,electric-dipole interactions,field pseudovector,enantiosensitive microwave spectroscopy,photoexcitation circular dichroism,molecular pseudoscalar,chiral discrimination,photoelectron circular dichroism
更新于2025-09-23 15:23:52
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Progress in development of a new luminescence setup at the FinEstBeAMS beamline of the MAX IV laboratory
摘要： FinEstBeAMS is a new materials science beamline at the 1.5 GeV storage ring of the MAX IV Laboratory in Lund, Sweden. It has been built based on grazing incidence monochromatization of synchrotron light, which allows to cover a remarkably wide excitation energy range from ultraviolet to soft x-rays (4.5-1450 eV). A new mobile luminescence spectroscopy end station has been commissioned with design benefitting from the advantages of a high flux elliptically polarizing undulator light source. We report on the design of the luminescence end station, its technical realization and performance achieved so far. Special attention is paid to the experimental challenges for luminescence spectroscopy under grazing incidence excitation conditions. The first luminescence results obtained demonstrate a reliable performance of the advanced setup at FinEstBeAMS.
关键词： Luminescence spectroscopy,synchrotron radiation,wide gap compounds,VUV – XUV photoexcitation
更新于2025-09-23 15:23:52
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Directly photoexcited Dirac and Weyl fermions in ZrSiS and NbAs
摘要： We report ultrafast optical measurements of the Dirac line-node semimetal ZrSiS and the Weyl semimetal NbAs, using mid-infrared pump photons from 86 meV to 500 meV to directly excite Dirac and Weyl fermions within the linearly dispersing bands. In NbAs, the photoexcited Weyl fermions initially form a non-thermal distribution, signi?ed by a brief spike in the differential re?ectivity whose sign is controlled by the relative energy of the pump and probe photons. In ZrSiS, electron-electron scattering rapidly thermalizes the electrons, and the spike is not observed. Subsequently, hot carriers in both materials cool within a few picoseconds. This cooling, as seen in the two materials’ differential re?ectivity, differs in sign, shape, and timescale. Nonetheless, we ?nd that it may be described in a simple model of thermal electrons, without free parameters. The electronic cooling in ZrSiS is particularly fast, which may make the material useful for optoelectronic applications.
关键词： ultrafast optical measurements,electronic cooling,photoexcitation,Dirac line-node semimetal,thermalization,Weyl semimetal
更新于2025-09-23 15:21:01
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Attosecond Dynamics of Photoexcitation of the Hydrogen Atom by Ultrashort Laser Pulses
摘要： The dynamics of photoexcitation of the hydrogen atom in the discrete and continuous spectra under the action of laser pulses in the attosecond range of time and pulse durations has been analyzed using perturbation theory. It is shown that over time interval shorter than or on the order of pulse duration, the time dependence of the photoexcitation probability is generally oscillating by nature. It has been established that for certain values of parameters, the envelope of this dependence has a peak, the position of which is determined by the pulse duration and carrier frequency.
关键词： Perturbation theory,Photoexcitation,Hydrogen atom,Attosecond dynamics,Ultrashort laser pulses
更新于2025-09-23 15:19:57
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Sub-millisecond Control of Neuronal Firing by Organic Light-Emitting Diodes
摘要： Optogenetics combines optics and genetics to enable minimally invasive cell-type-specific stimulation in living tissue. For the purposes of bio-implantation, there is a need to develop soft, flexible, transparent and highly biocompatible light sources. Organic semiconducting materials have key advantages over their inorganic counterparts, including low Young’s moduli, high strain resistances, and wide color tunability. However, until now it has been unclear whether organic light emitting diodes (OLEDs) are capable of providing sufficient optical power for successful neuronal stimulation, while still remaining within a biologically acceptable temperature range. Here we investigate the use of blue polyfluorene- and orange poly(p-phenylenevinylene)-based OLEDs as stimuli for blue-light-activated Sustained Step Function Opsin (SFFO) and red-light-activated ChrimsonR opsin, respectively. We show that, when biased using high frequency (multi-kHz) drive schemes, the OLEDs permit safe and controlled photostimulation of opsin-expressing neurons and were able to control neuronal firing with high temporal-resolution at operating temperatures lower than previously demonstrated.
关键词： neurons,photoexcitation,electrophysiology,pulsed-operation,bioelectronics,organic light-emitting diodes,optical stimulation,optogenetics
更新于2025-09-11 14:15:04
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) formation: Comparison with
摘要： Superexcited states of H2S have been investigated with determining the cross sections for emission of dispersed and nondispersed atomic ?uorescence against the incident photon energy in the range 11–40 eV to address the ionization and excitation of the valence electrons. This method enables us to extract the discrete electronic state from the superposition with continuous electronic states. The cross sections for H(2p) formation have been put on an absolute scale. Ten superexcited states have been found, two in the range 13–15 eV are singly excited 2b?1 2 (mo) states with a single con?guration and the other eight states in the range 16–25 eV are doubly excited states with multiple con?gurations. State-resolved dipole oscillator strengths for H(2p) formation in the photoexcitation of H2S have been determined. Similar experiments have been performed for H2O. The state-resolved dipole oscillator strengths for H(2p) formation in the photoexcitation of H2S are ～10?3, whereas those in the photoexcitation of H2O range from ～10?3 to ～10?2. It is found that major fragment atoms are H(2p) atoms in the photoexcitation of H2O and S? in the photoexcitation of H2S. The superexcited states of H2O and H2S are compared based on the similarity and difference of the electronic structures. It turns out from the comparison that (i) the smaller values of the dipole oscillator strengths for H(2p) formation in the photoexcitation of H2S are related to the change of the major fragment atoms and (ii) the energy splitting of the doubly excited “4a?1 1 (mo(cid:4))” states of H2O. This enhancement is caused by the stronger electron correlation in H2S than in H2O. The similarity in shape is indicated between the inner valence band and inner shell band in the ?uorescence cross sections against the incident photon energy for H2S and H2O.
关键词： superexcited states,H2O,dipole oscillator strengths,electron correlation,H2S,double photoexcitation
更新于2025-09-09 09:28:46
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Measuring Complex for the Diagnostics of the Quality of Light–Emitting Heterostructures According to Photoelectric and Optical Responses Under Local Photoexcitation
摘要： We propose an automated measuring complex for the diagnostics of the lateral homogeneity of semiconductor heterostructures by measurements and analysis of the photoelectric and optic responses to their local photoexcitation in static and dynamic modes. The electronic-mechanical and optical positioning systems guarantee the illumination of local region of the investigated structure with a minimum diameter of the spot of 14 μm and a positioning accuracy of 10 μm. It is shown that the measuring complex can be used for the diagnostics of the quality of light-emitting heterostructures, transistors, solar cells, and photodiodes.
关键词： local photoexcitation,light-emitting heterostructures,photoelectric response,quality diagnostics,lateral heterogeneity,automated installation
更新于2025-09-09 09:28:46
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Non-equilibrium photoexcited carrier effects in a graphene-based Josephson junction
摘要： We studied the superconducting proximity effect under photoexcitation by illuminating a superconductor/monolayer graphene/superconductor (SGS) Josephson junction with monochromatic light at a wavelength of 1.31 lm. Although the critical current Ic can be controlled by the irradiation power P, its variation cannot be explained by modi?cation of the carrier density, which has been reported for semiconductor-based Josephson junctions. The estimated electron temperature of gra- phene is proportional to Pd, where d ’ 1=3. This relation clearly indicates that photogenerated non- equilibrium carrier dynamics are responsible for the variation of Ic with P. We suggest that the SGS junction can directly mediate interactions between the optical ?eld and the superconducting state.
关键词： electron temperature,photoexcitation,critical current,graphene,Josephson junction,superconducting proximity effect
更新于2025-09-09 09:28:46