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How the methyl group position influences the ultrafast deactivation in aromatic radicals
摘要： Excited xylyl (methyl–benzyl) radical isomers have been studied by femtosecond time-resolved photoelectron spectroscopy and mass spectrometry. Depending on the substitution we find different deactivation channels after excitation into the D3(2A00) state (310 nm, 4 eV). While the ortho and para isomer exhibit deactivation rates similar to the benzyl radical, meta-xylyl sticks out and depletes twice as fast into the vibrationally hot ground state. We found that a ring deformation mode rather than the methyl pseudorotation enables access to a conical intersection, which is responsible for the faster deactivation. Transitions in the photoelectron spectrum can be assigned to several Rydberg series with mostly d angular momentum components. Absorption of two 4 eV photons triggers hydrogen loss reactions on a femtosecond timescale.
关键词： photoelectron spectroscopy,mass spectrometry,conical intersection,Rydberg states,femtosecond spectroscopy,ultrafast deactivation,xylyl radicals
更新于2025-09-19 17:15:36
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Evidence of ac-Stark-shifted resonances in intense two-color circularly polarized laser fields
摘要： We report on the appearance of a structure at low energies in the photoelectron momentum distribution of the hydrogen atom exposed to two-color counterrotating bicircular laser fields. These structures, which arise due to ac-Stark-shifted resonances, break the threefold symmetry, typical for the ω ? 2ω bicircular fields. We discuss the physical origin of this structure in terms of partial-wave interference between direct ionization channels and a resonant pathway, which passes through the ac-Stark-shifted state, and show how the underlying Rydberg state population depend on the field strength and pulse duration.
关键词： bicircular laser fields,Rydberg state population,ac-Stark-shifted resonances,photoelectron momentum distribution,hydrogen atom
更新于2025-09-19 17:13:59
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Rydberg-State-Resolved Resonant Energy Transfer in Cold Electric-Field-Controlled Intrabeam Collisions of NH <sub/>3</sub> with Rydberg He Atoms
摘要： The resonant transfer of energy from the inversion sublevels in NH3 to He atoms in triplet Rydberg states with principal quantum number n = 38 has been controlled using electric fields below 15 V/cm in intrabeam collisions at translational temperatures of ～1 K. The experiments were performed in pulsed supersonic beams of NH3 seeded in He at a ratio of 1:19. The He atoms were prepared in the metastable 1s2s 3S1 level in a pulsed electric discharge in the trailing part of the beams. The velocity slip between the heavy NH3 and the lighter metastable He was exploited to perform collision studies at center-of-mass collision speeds of ～70 m/s. Resonant energy transfer in the atom?molecule collisions was identified by Rydberg-state-selective electric-field ionization. The experimental data have been compared to a theoretical model of the resonant dipole?dipole interactions between the collision partners based on the impact parameter method.
关键词： NH3,resonant energy transfer,cold collisions,electric-field control,Rydberg states,He
更新于2025-09-12 10:27:22
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[IEEE 2019 Antenna Measurement Techniques Association Symposium (AMTA) - San Diego, CA, USA (2019.10.6-2019.10.11)] 2019 Antenna Measurement Techniques Association Symposium (AMTA) - Waveguide-integrated Rydberg Atom-based RF Field Detector for Near-field Antenna Measurements
摘要： We demonstrate simultaneous amplitude and phase measurements of a radio-frequency (RF) ?eld through the use of a Rydberg atom-based sensor embedded inside a waveguiding structure. This measurement uses the Rydberg atom-based sensor in a mixer con?guration, which requires the presence of a local oscillator (LO) RF ?eld. The waveguiding structure supplies the LO ?eld. The combined waveguide and Rydberg atom system is used to measure phase and amplitude in the near-?eld of a horn antenna to extract the far-?eld pattern.
关键词： far-field pattern,near-field antenna measurements,waveguide,Rydberg atom-based sensor,RF field measurements
更新于2025-09-12 10:27:22
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Symmetry of molecular Rydberg states revealed by XUV transient absorption spectroscopy
摘要： Transient absorption spectroscopy is utilized extensively for measurements of bound- and quasibound-state dynamics of atoms and molecules. The extension of this technique into the extreme ultraviolet (XUV) region with attosecond pulses has the potential to attain unprecedented time resolution. Here we apply this technique to aligned-in-space molecules. The XUV pulses are much shorter than the time during which the molecules remain aligned, typically <100 fs. However, transient absorption is not an instantaneous probe, because long-lived coherences re-emit for picoseconds to nanoseconds. Due to dephasing of the rotational wavepacket, it is not clear if these coherences will be evident in the absorption spectrum, and whether the properties of the initial excitations will be preserved. We studied Rydberg states of N2 and O2 from 12 to 23 eV. We were able to determine the polarization direction of the electronic transitions, and hence identify the symmetry of the final states.
关键词： transient absorption spectroscopy,extreme ultraviolet,attosecond pulses,molecular alignment,Rydberg states
更新于2025-09-11 14:15:04
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[IEEE 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018) - Paris, France (2018.7.8-2018.7.13)] 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018) - Measurement of the Rydberg Constant with Trapped Rydberg Atoms
摘要： A measurement of the Rydberg constant using cold circular Rydberg atoms is proposed. Since these atoms have long lifetimes, negligible quantum electrodynamics and no nuclear-overlap corrections, the measurement can shed new light on the “proton radius puzzle”. The atoms are trapped in an optical lattice. Transitions are driven using a lattice-modulation technique to perform Doppler-free sub-THz spectroscopy; the transition frequencies yield the Rydberg constant. The selected transitions are free of ?rst-order Zeeman and Stark shifts. Systematic uncertainties due to lattice-induced shifts, core-polarization, second-order Zeeman and Stark shifts, etc are estimated.
关键词： optical lattice,proton radius,sub-THz spectroscopy,Rydberg constant,precision measurements,Rydberg atoms
更新于2025-09-10 09:29:36
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Optical switching phenomenon in ladder type atomic system under varying wavelength mismatching effect with one due to a Rydberg transition
摘要： We present a theoretical study on probe field propagation through a three-level ? type system formed in an atomic vapor medium in presence of a strong control field. The model is based on density matrix method and is solved analytically, without neglecting any term in any power of probe and control Rabi frequencies, to find out the probe response under Doppler free condition as well as at room temperature. The probe response for a four-level ? type system is also determined analytically. Electromagnetically induced transparency is formed in the simulated probe response for both the level schemes. We also present the switching of probe field propagation from subluminal to superluminal as a function of probe detuning for different control transitions, one of which is to a Rydberg state. The switching window becomes asymmetric under detuned control field with the asymmetry depending on the wavelength mismatching factor between the control field and the probe field. Under strong probe regime probe propagation switches from superluminal to subluminal on resonance when the wavelength mismatch between the probe and the control field is increased, an effect which can be explained with the help of the analytical model that is free from any perturbative treatment.
关键词： wavelength mismatching effect,electromagnetically induced transparency,Rydberg state,optical switching,Ladder (?) type system
更新于2025-09-10 09:29:36
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Evolution of Atomic Entanglement for Different Cavity-Field Statistics in Single-Mode Two-Photon Process
摘要： We study the evolution of entanglement for a pair of two-level Rydberg atoms passing one after the other into an ideal cavity filled with a single mode radiation field. The atoms interact with the cavity field via two-photon transitions. The initial joint state of two atoms that enter the cavity one after the other is unentangled. Interactions intervened by the single mode cavity photon field brings out the final two-atom mixed entangled type state. We use the well known measure appropriate for the mixed states, i.e. the entanglement of formation to quantify the entanglement. We calculate the entanglement of formation of the joint two-atom state as a function of the Rabi angle, for the Fock state field, coherent field and thermal field respectively inside the cavity. The change in the magnitude of atomic entanglement with cavity photon number has been discussed.
关键词： cavity quantum electrodynamics,two-photon transitions,entanglement of formation,entanglement,Rydberg atoms
更新于2025-09-10 09:29:36
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[IEEE 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018) - Paris, France (2018.7.8-2018.7.13)] 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018) - High-Intensity Electric Field Measurements with Rydberg Vapors
摘要： Measurements of radio-frequency (RF) electric fields using EIT spectroscopy of Rydberg states in atomic vapors have garnered significant interest in recent years. Here we describe recent work extending the approach to measurements of high-intensity RF electric fields above 1 kV/m and continuous-frequency RF measurement capability.
关键词： RF,metrology,electric field measurements,quantum sensors,Rydberg atoms
更新于2025-09-10 09:29:36
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Photoluminescence properties of the entire excitonic series in
摘要： We investigated the photoluminescence spectra of Cu2O under photoexcitation at 3.05 eV across the violet band gap. The following three features were found: photoluminescence from blue and violet excitons; photoluminescence from yellow excitons of s, d, and f states in addition to p states with a quantum number up to ten; and emissions associated with the inelastic collision of the 1s yellow excitons. The first process is relevant for the separation of radiative and nonradiative decay rates. The second process likely indicates radiative enhancement of high Rydberg yellow excitons. The last process verifies up-conversion of 1s yellow paraexcitons into higher Rydberg states, which is a critical factor impeding the realization of a high-density paraexciton gas towards transition to the Bose-Einstein condensation.
关键词： photoluminescence,Rydberg states,excitons,Bose-Einstein condensation,Cu2O
更新于2025-09-10 09:29:36