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Light absorption by surface nanoholes and nanobumps
摘要： This paper deals with a numerical investigation of the energy deposition induced by ultrafast laser interaction with nanostructures. We calculate and analyze the intensity near-field reactive and radiative patterns resulted from the interference of the incident light with light scattered by individual subwavelength holes and bumps on the surface of metallic and dielectric materials. The role of light polarization, optical material properties, collective effects and nature of the imperfections in localized energy absorption is elucidated. The results open new perspectives in precise light manipulation by surface inhomogeneities and well-controlled surface nanostructuring by ultrashort laser.
关键词： light absorption,surface nanoholes,ultrafast laser,nanostructures,nanobumps
更新于2025-09-10 09:29:36
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Sub-20 fs All-Optical Switching in a Single Au-Clad Si Nanodisk
摘要： Dielectric nanoantennas have recently emerged as promising elements for nonlinear and ultrafast nanophotonics due to their ability to concentrate light on the nanometer scale with low losses, while exhibiting large nonlinear susceptibilities. In this work, we demonstrate that single Si nanodisks covered with a thin 30-nm thick layer of Au can generate positive and negative sub-20 fs reflectivity modulations of ?0.3% in the vicinity of the first-order anapole mode, when excited around the second-order anapole mode. The experimental results, characterized in the visible to near infrared spectral range, suggest that the nonlinear optical Kerr effect is the responsible mechanism for the observed all-optical switching phenomena. These findings represent an important step toward nanoscale ultrafast all-optical signal processing.
关键词： anapole modes,optical Kerr effect,ultrafast all-optical switching,pump-probe spectroscopy,Dielectric nanoantennas
更新于2025-09-10 09:29:36
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Light for brevity
摘要： The shortest time interval controlled by a human being is the duration of a light pulse as short as only 100 attoseconds, i.e., 10-16 s. This “attosecond” light pulse belongs to the extreme ultraviolet range (XUV) of the electromagnetic spectrum, with central photon energy typically between 20 and 200 eV. Related to its brevity, an attosecond pulse has a broad bandwidth covering tens of eV. These are natural time and energy scales to study electron dynamics in atoms and molecules.
关键词： ultrafast atomic and molecular physics,high-order harmonic generation,attosecond pulses,electron dynamics
更新于2025-09-10 09:29:36
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Ultrashort pulse reconstruction using a deterministic phase retrieval method with Gaussian-envelope gates
摘要： A novel scheme of ultrashort pulse characterization is proposed that is capable of reconstructing the complex-valued envelope of a pulse in the time domain by use of a second harmonic generation system with two Gaussian gate pulses. In this scheme, we apply an analytic (noniterative) phase-retrieval method for coherent diffractive imaging in the space domain to the pulse characterization, and so the spectral phase of an unknown pulse can be retrieved from only two spectra of the unknown pulse modulated with a Gaussian gate and its time-shifted Gaussian one. Computer-simulated examples demonstrate that the pulse retrieval is robust. In particular, it is shown that the reconstruction of an unknown pulse using approximate Gaussian gates derived from replicas of the pulse itself is also effective, provided the spectrum of the unknown pulse has a gentle slope within the spectral bandwidth of the gate pulse.
关键词： Ultrafast measurements,Pulse characterization,Phase retrieval,Ultrafast optics
更新于2025-09-09 09:28:46
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Non-linear soft x-ray methods on solids with MUSIX—the multi-dimensional spectroscopy and inelastic x-ray scattering endstation
摘要： With the intense and coherent x-ray pulses available from free-electron lasers, the possibility to transfer non-linear spectroscopic methods from the laser lab to the x-ray world arises. Advantages especially regarding selectivity and thus information content as well as an improvement of signal levels are expected. The use of coherences is especially fruitful and the example of coherent x-ray/optical sum-frequency generation is discussed. However, many non-linear x-ray methods still await discovery, partially due to the necessity for extremely adaptable and versatile instrumentation that can be brought to free-electron lasers for the analysis of the spectral content emitted from the sample into a continuous range of emission angles. Such an instrument (called MUSIX) is being developed and employed at FLASH, the free-electron laser in Hamburg and is described in this contribution together with first results.
关键词： free-electron lasers,x-ray instrumentation,x-ray spectroscopy,ultrafast dynamics
更新于2025-09-09 09:28:46
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in light filaments
摘要： We present our results on the emissions from N2+ pumped with ultrafast filaments using high-resolution pump probe. Our result shows the phase relation between transition lines at earlier delays. We show that the gain on transition lines extends beyond the time when coherence is lost.
关键词： stimulated emission,N2+,rotational wave packet,light filaments,ultrafast pump probe
更新于2025-09-09 09:28:46
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Ultrafast carbon monoxide photolysis and heme spin-crossover in myoglobin via nonadiabatic quantum dynamics
摘要： Light absorption of myoglobin triggers diatomic ligand photolysis and a spin crossover transition of iron(II) that initiate protein conformational change. The photolysis and spin crossover reactions happen concurrently on a femtosecond timescale. The microscopic origin of these reactions remains controversial. Here, we apply quantum wavepacket dynamics to elucidate the ultrafast photochemical mechanism for a heme–carbon monoxide (heme–CO) complex. We observe coherent oscillations of the Fe–CO bond distance with a period of 42 fs and an amplitude of ～1 ?. These nuclear motions induce pronounced geometric reorganization, which makes the CO dissociation irreversible. The reaction is initially dominated by symmetry breaking vibrations inducing an electron transfer from porphyrin to iron. Subsequently, the wavepacket relaxes to the triplet manifold in ～75 fs and to the quintet manifold in ～430 fs. Our results highlight the central role of nuclear vibrations at the origin of the ultrafast photodynamics of organometallic complexes.
关键词： Ultrafast carbon monoxide photolysis,nonadiabatic quantum dynamics,myoglobin,heme spin-crossover
更新于2025-09-09 09:28:46
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Ultrafast nuclear dynamics in the doubly-core-ionized water molecule observed via Auger spectroscopy
摘要： We present a combined experimental and theoretical study of the Auger-emission spectrum following double core ionization and excitation of gas-phase water molecules with hard-x-ray synchrotron radiation above the O K ?2 threshold. We observe an indication of ultrafast proton motion occurring within the 1.5 fs lifetime of the double-core-hole (DCH) states in water. Furthermore, we have identi?ed symmetric and antisymmetric dissociation modes characteristic for particular DCH states. Our results serve as a fundamental reference for state-of-the-art studies of DCH dynamic processes in liquid water both at synchrotron and free-electron-laser facilities.
关键词： double core ionization,Auger-emission spectrum,synchrotron radiation,ultrafast proton motion,DCH states
更新于2025-09-09 09:28:46
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Arbitrary amplitude femtosecond pulse shaping via a digital micromirror device
摘要： An ultrafast spectrum programmable femtosecond laser may enhance the performance of a wide variety of scientific applications, e.g., multi-photon imaging. In this paper, we report a digital micromirror device (DMD)-based ultrafast pulse shaper, i.e., DUPS, for femtosecond laser arbitrary amplitude shaping — the first time a programmable binary device reported to shape the amplitudes of ultrafast pulses spectrum at up to 32 kHz rate over a broad wavelength range. The DUPS is highly efficient, compact, and low cost based on the use of a DMD in combination with a transmission grating. Spatial and temporal dispersion introduced by the DUPS is compensated by a quasi-4-f setup and a grating pair, respectively. Femtosecond pulses with arbitrary spectrum shapes, including rectangular, sawtooth, triangular, double-pulse, and exponential profile, have been demonstrated in our experiments. A feedback operation process is implemented in the DUPS to ensure a robust and repeatable shaping process. The total efficiency of the DUPS for amplitude shaping is measured to be 27%.
关键词： digital micromirror device,Spectrum shaping,ultrafast laser
更新于2025-09-09 09:28:46
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Ultrafast Nonadiabatic Cascade and Subsequent Photofragmentation of Extreme Ultraviolet Excited Caffeine Molecule
摘要： Ultrafast XUV-chemistry is offering new opportunities to decipher the complex dynamics taking place in highly excited molecular states and thus better understand fundamental natural phenomena as molecule formation in interstellar media. We used ultrashort XUV light pulses to perform XUV-pump–IR-probe experiments in caffeine as a model of prebiotic molecule. We observed a 40-fs decay of excited cationic states. Guided by quantum calculations, this timescale is interpreted in terms of a non-adiabatic cascade through a large number of highly correlated states. This shows that the correlation driven non-adiabatic relaxation seems to be a general process for highly excited states, which might impact our understanding of molecular processing in interstellar media.
关键词： non-adiabatic cascade,quantum calculations,Ultrafast XUV-chemistry,interstellar media,caffeine
更新于2025-09-09 09:28:46