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Photoexcitation
About: Photoexcitation is a research topic. Over the lifetime, 5874 publications have been published within this topic receiving 134733 citations.
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TL;DR: For photon energies exceeding 10 eV a new dissociation scheme is identified in which photoabsorption leads to a fast loss of the tyrosine side chain, which leads to the formation of a residual peptide that is remarkably cold internally.
Abstract: Until now, photodissociation studies on free complex protonated peptides were limited to the UV wavelength range accessible by intense lasers. We have studied photodissociation of gas-phase protonated leucine-enkephalin cations for vacuum ultraviolet (VUV) photons energies ranging from 8 to 40 eV. We report time-of-flight mass spectra of the photofragments and various photofragment-yields as a function of photon energy. For sub-ionization energies our results are in line with existing studies on UV photodissociation of leucine-enkephalin. For photon energies exceeding 10 eV we could identify a new dissociation scheme in which photoabsorption leads to a fast loss of the tyrosine side chain. This loss process leads to the formation of a residual peptide that is remarkably cold internally.
79 citations
TL;DR: This work reports the dynamics of photoinduced carriers in a free-standing MoS2 laminate using time-resolved optical pump-terahertz probe spectroscopy and provides a comprehensive understanding of the non-equilibrium carrier kinetics in a system of unscreened Coulomb interactions.
Abstract: We report the dynamics of photoinduced carriers in a free-standing MoS2 laminate consisting of a few layers (1-6 layers) using time-resolved optical pump-terahertz probe spectroscopy. Upon photoexcitation with the 800 nm pump pulse, the terahertz conductivity increases due to absorption by the photoinduced charge carriers. The relaxation of the non-equilibrium carriers shows fast as well as slow decay channels, analyzed using a rate equation model incorporating defect-assisted Auger scattering of photoexcited electrons, holes, and excitons. The fast relaxation time occurs due to the capture of electrons and holes by defects via Auger processes, resulting in nonradiative recombination. The slower relaxation arises since the excitons are bound to the defects, preventing the defect-assisted Auger recombination of the electrons and the holes. Our results provide a comprehensive understanding of the non-equilibrium carrier kinetics in a system of unscreened Coulomb interactions, where defect-assisted Auger processes dominate and should be applicable to other 2D systems.
78 citations
TL;DR: A series of dyad and triad donor-acceptor molecules in which 2J is measured directly as a function of incremental changes in their structures, which shows directly that the recombination rates in these molecules obey an exponential distance dependence.
Abstract: The spin−spin exchange interaction, 2J, in a radical ion pair produced by a photoinduced electron transfer reaction can provide a direct measure of the electronic coupling matrix element, V, for the subsequent charge recombination reaction. We have developed a series of dyad and triad donor−acceptor molecules in which 2J is measured directly as a function of incremental changes in their structures. In the dyads the chromophoric electron donors 4-(N-pyrrolidinyl)- and 4-(N-piperidinyl)naphthalene-1,8-dicarboximide, 5ANI and 6ANI, respectively, and a naphthalene-1,8:4,5-bis(dicarboximide) (NI) acceptor are linked to the meta positions of a phenyl spacer to yield 5ANI−Ph−NI and 6ANI−Ph−NI. In the triads the same structure is used, except that the piperidine in 6ANI is replaced by a piperazine in which a para-X−phenyl, where X = H, F, Cl, MeO, and Me2N, is attached to the N‘ nitrogen to form a para-X-aniline (XAn) donor to give XAn−6ANI−Ph−NI. Photoexcitation yields the respective 5ANI+−Ph−NI-, 6ANI+−Ph−NI-, ...
78 citations
TL;DR: In this article, the authors demonstrate ultrafast dynamical tuning of resonance in the terahertz (THz) frequency range in YBa_2Cu_3O_7-\delta (YBCO) split-ring resonator arrays excited by near-infrared femtosecond laser pulses.
Abstract: Through the integration of semiconductors or complex oxides into metal resonators, tunable metamaterials have been achieved by a change of environment using an external stimulus. Metals provide high conductivity to realize a strong resonant response in metamaterials; however, they contribute very little to the tunability. The complex conductivity in high-temperature superconducting films is highly sensitive to external perturbations, which provides new opportunities in achieving tunable metamaterials resulting directly from the resonant elements. Here we demonstrate ultrafast dynamical tuning of resonance in the terahertz (THz) frequency range in YBa_2Cu_3O_7-\delta (YBCO) split-ring resonator arrays excited by near-infrared femtosecond laser pulses. The photoexcitation breaks the superconducting Cooper pairs to create the quasiparticle state. This dramatically modifies the imaginary part of the complex conductivity and consequently the metamaterial resonance in an ultrafast timescale. We observed resonance switching accompanied with a wide range frequency tuning as a function of photoexcitation fluence, which also strongly depend on the nano-scale thickness of the superconducting films. All of our experimental results are well reproduced through calculations using an analytical model, which takes into account the SRR resistance and kinetic inductance contributed from the complex conductivity of YBCO films. The theoretical calculations reveal that the increasing SRR resistance upon increasing photoexcitation fluence is responsible for the reduction of resonance strength, and both the resistance and kinetic inductance contribute to the tuning of resonance frequency.
78 citations
TL;DR: In this article, the authors investigated the early relaxation dynamics of the equilibrated hydrated electron within the first 200 fs upon photoexcitation using photon echo techniques and showed that even for extremely short pulse durations, the signals obtained in photon echo spectroscopy can be described in the conventional way, provided care is taken of the spectral filtering effect and experimental beam arrangement.
Abstract: Employing photon echo techniques, we investigate the early relaxation dynamics of the equilibrated hydrated electron within the first 200 fs upon photoexcitation. The use of 5-fs laser pulses provided unprecedented temporal resolution of our measurements. We show that even for extremely short pulse durations the signals obtained in photon echo spectroscopy, can be described in the conventional way, provided care is taken of the spectral filtering effect and experimental beam arrangement. We next conclude that the absorption spectrum of the hydrated electrons is primarily homogeneously broadened. The comparison of two pulse photon echo experiments on pure water and on hydrated electrons allows us to measure the pure dephasing time of ∼1.6 fs. The line shape of the absorption spectrum is described excellently by an extended Lorentzian contour with a spectral width fully determined by the pure dephasing time. From the polarization-dependent transient grating experiments we establish that the polarization ani...
78 citations