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[IEEE 2019 IEEE Photonics Conference (IPC) - San Antonio, TX, USA (2019.9.29-2019.10.3)] 2019 IEEE Photonics Conference (IPC) - High-Power Ultrafast Industrial Thin-Disk Lasers
摘要： Ultrafast amplifiers using industrial thin-disk technology from TRUMPF deliver record pulse energies of 200 mJ at 5 kHz. In addition, multipass amplifiers to increase the average power and pulse energy and concepts for nonlinear compression to reach pulse durations below 50 fs will be discussed.
关键词： diode-pumped,ultrafast,high-energy,Thin-disk laser,amplification,high-power,laser amplifier,X-ray
更新于2025-09-11 14:15:04
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[IEEE 2019 IEEE Photonics Conference (IPC) - San Antonio, TX, USA (2019.9.29-2019.10.3)] 2019 IEEE Photonics Conference (IPC) - Effects of the Pump Wavelength on Laser-Induced Ultrafast Demagnetization
摘要： A high harmonics source is used to perform x-ray resonant magnetic scattering on a magnetic sample. The dynamics of laser-induced ultrafast demagnetization are probed with respect to the wavelength of the pump beam. Longer pump wavelengths are found to increase the initial quenching levels.
关键词： high harmonics generation,magnetic dynamics,ultrafast demagnetization
更新于2025-09-11 14:15:04
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Ultrafast Structural Dynamics of Nanoparticles in Intense Laser Fields
摘要： Femtosecond laser pulses have opened new frontiers for the study of ultrafast phase transitions and nonequilibrium states of matter. In this Letter, we report on structural dynamics in atomic clusters pumped with intense near-infrared (NIR) pulses into a nanoplasma state. Employing wide-angle scattering with intense femtosecond x-ray pulses from a free-electron laser source, we find that highly excited xenon nanoparticles retain their crystalline bulk structure and density in the inner core long after the driving NIR pulse. The observed emergence of structural disorder in the nanoplasma is consistent with a propagation from the surface to the inner core of the clusters.
关键词： x-ray scattering,nanoparticles,nanoplasma,intense laser fields,ultrafast structural dynamics
更新于2025-09-11 14:15:04
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RMT: R-matrix with time-dependence. Solving the semi-relativistic, time-dependent Schr?dinger equation for general, multielectron atoms and molecules in intense, ultrashort, arbitrarily polarized laser pulses
摘要： RMT is a program which solves the time-dependent Schr?dinger equation for general, multielectron atoms, ions and molecules interacting with laser light. As such it can be used to model ionization (single-photon, multiphoton and strong-field), recollision (high-harmonic generation, strong-field rescattering) and, more generally, absorption or scattering processes with a full account of the multielectron correlation effects in a time-dependent manner. Calculations can be performed for targets interacting with ultrashort, intense laser pulses of long wavelength and arbitrary polarization. Calculations for atoms can optionally include the Breit-Pauli correction terms for the description of relativistic (in particular, spin-orbit) effects.
关键词： electron correlation,R-matrix,ionization,strong-field physics,ultrafast physics,Attosecond physics
更新于2025-09-11 14:15:04
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Field emission microscopy pattern of a single-crystal diamond needle under ultrafast laser illumination
摘要： We report herein on the spatial beam properties of a ?eld emission electron source based on a single-crystal diamond needle illuminated by ultrashort light pulses. We show that the increasing of the laser intensity strongly modi?es the emission pattern, leading to the emergence of a new emission region at high peak power. This region is situated on the opposite side of the diamond needle to the one irradiated by the laser. By spatially-resolved energy spectrometry, we prove that the electrons emitted from this region are governed by a multi-photon absorption process. The occurrence of this emission pattern can be explained by accounting for the inhomogeneous distribution of the optical ?eld enhancement and the laser absorption induced by light diffraction within the nanometric needle. The numerical simulations performed on a real sub-wavelength tip con?rm this localization of the optical ?eld enhancement and reveal that the electrons trajectories match the spatial beam distribution evidenced experimentally. This work underlines the need to closely monitor the surface roughness of the ?eld emitter as well as the laser illumination conditions to ?nely control its emission pattern.
关键词： ?eld emission,diamond,ultrafast laser,electron spectroscopy,nanoemitters
更新于2025-09-11 14:15:04
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Femtosecond transient absorption spectroscopy of laser-ablated graphite and reduced graphene oxide for optical switching behavior
摘要： Carbon based materials are considered as a rewarding contestant for optical devices due to its novel properties. In this study, graphite is laser-ablated and di?erent analytical methods such as XRD and Raman spectroscopy are used to evaluate the crystalline nature. In XRD, it indicates the decreased intensity after laser ablation but no change in peak positions resulted as graphite is very strong and hard material. Scanning electron microscopy (SEM) used to evaluate structural characteristics shows the overlapping layered structure after ablation. Reduced graphene oxide (rGO) is prepared by using modi?ed Hummers' method and reduced it by thermal reduction method. UV–Vis spectra con?rmed the peaks of graphite and rGO at 274 nm and 267 nm, respectively. To study the carrier relaxation dynamics of graphite and rGO, ultrafast Visible-pump/NIR-probe femtosecond transient absorption spectroscopy was used. Carrier relaxation occurred between 260 and 309 fs even after laser ablation damage, which is useful for future application of optical switching under high laser repetition.
关键词： Optical switching,Graphite,Graphene,Laser ablation,Transient absorption spectroscopy,Ultrafast spectroscopy
更新于2025-09-11 14:15:04
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Ultrafast Broadband Diagnostics of the Filling of the s Band at the Two-Photon Femtosecond Laser Excitation of a Gold Film
摘要： The transmission of near infrared femtosecond laser pulses (wavelength of 800 nm) and supercontinuum radiation (300–750 nm) generated by them through a 50-nm gold film immersed in water has been experimentally studied at the power of focused laser radiation in the range of 1–10 GW. An increase in the excitation intensity is accompanied by the blueshift of the edge of the extinction band of the film, which is attributed to the filling of electronic states of the s band with a low density of states caused by two-photon interband transitions from d bands with a high density of states.
关键词： supercontinuum radiation,gold film,ultrafast broadband diagnostics,s band filling,two-photon femtosecond laser excitation
更新于2025-09-11 14:15:04
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Ultrafast Dynamics and Ultrasensitive Single-Particle Intermittency in Small-Sized Toxic Metal Free InP Based Core/Alloy-shell/Shell Quantum Dots: Excitation Wavelength Dependency Towards Variation of PLQY
摘要： Observation of strong deviation of photoluminescence excitation curve from absorption curve specially at lower wavelength range, below 450 nm in case of small sized toxic metal free InP based core-alloy-shell quantum dots hints towards interesting exciton dynamics. PL quantum yield (PLQY) has been observed to be dependent on the excitation wavelength. Monitoring the bleach dynamics employing femtosecond ultrafast pump-probe technique it could be shown that the rise-time increases with decrease in pump excitation wavelength from 100 fs for 550 nm excitation to 220 fs for 430 nm pump/excitation. Therefore exciton cooling takes longer time for lower wavelength excitation and thus the exciton becomes more prone to get trapped. About two fold enhancement in magnitude of normalized bleach signal at the band edge (~0.1 (for 430nm excitation) to ~0.2 (for 550nm excitation)) following exciton relaxation has been observed. Thus, in comparison to lower wavelength excitation, for near band-edge pump/excitation there is higher probability of radiative exciton recombination, therefore increasing PLQY. Hot exciton trapping dynamics has been noted to be occurring at a timescale ~750 fs. From ultra-sensitive single particle measurement, magnitude of power-law exponent for both ON and OFF events remain similar to each other and the magnitude remains unaltered for different excitation wavelengths, (405 nm to 568 nm). As long as 100 s ON event could be observed making this InP based non-toxic QD quite suitable for single particle tracking etc. Interestingly, ON event truncation time has been found to increase from 6s to 16s and OFF event truncation time has been found to decrease from 11s to 5.5s, thereby exciton detrapping rate / trapping rate increases from 0.5 to nearly 3 on going from 405 nm to 568 nm excitation. Thus, as the trapping gets suppressed and detrapping gets enhanced, PLQY gets enhanced. The extent of relative decrease of PLQY value with increase in excitation energy above band-edge has been observed to be much more pronounced in CdSe based CAS QD than InP based CAS QD.
关键词： ultrafast dynamics,photoluminescence quantum yield,excitation wavelength dependency,InP based quantum dots,single-particle intermittency
更新于2025-09-11 14:15:04
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Femtosecond laser-induced non-centrosymmetric surface microstructures on bulk metallic glass for unidirectional droplet micro-displacement
摘要： Unidirectional droplet motion without energy input has attracted considerable attention in various potential applications. We report on the fabrication of unconventional laser-induced periodic surface structures (LIPSS) for unidirectional droplet micro-displacement by femtosecond laser at large incident angle. In order to overcome the mechanical durability of the existing soft materials such as PDMS for controlling the droplet, Zr-based bulk metallic glass (Zr-BMG) is used to fabricate the typical non-centrosymmetric unconventional LIPSS, which include micro-sized elliptical arc-shaped structures and nano-ripples with the central spatial periodicity of 400 nm. The spots and the grating of unconventional LIPSS on Zr-BMG are fabricated to construct the functional surface structures by femtosecond laser irradiation. The unidirectional micro-displacement of water droplet on Zr-BMG was achieved using functional surface structures. For better understanding the fabrication of unconventional LIPSS, the underlying formation mechanism was revealed by numerical simulations. This work gives a fast, precise and low-cost method to fabricate the non-centrosymmetric surface micro/nano-structures on metal materials for unidirectional droplet motion in microfluidics.
关键词： laser surface structuring,unidirectional droplet motion,LIPSS,bulk metallic glass,Ultrafast laser
更新于2025-09-11 14:15:04
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Plasmonic Lenses for Tunable Ultrafast Electron Emitters at the Nanoscale
摘要： Simultaneous spatiotemporal con?nement of energetic electron pulses to femtosecond and nanometer scales is a topic of great interest in the scienti?c community, given the potential impact of such developments across a wide spectrum of scienti?c and industrial applications. For example, in ultrafast electron scattering, nanoscale probes would enable accurate maps of structural dynamics in materials with nanoscale heterogeneity, thereby leading to an understanding of the role of boundaries and defects on macroscopic properties. On the other hand, advances in this ?eld are mostly limited by the brightness and size of the electron source. We present the design, fabrication, and optical characterization of bullseye plasmonic lenses for next-generation ultrafast electron sources. Using electromagnetic simulations, we examine how the interplay between light-plasmon coupling, plasmon propagation, dispersion, and resonance governs the properties of the photoemitted electron pulse. We also illustrate how the pulse duration and strength can be tuned by geometric design and predict that sub-10-fs pulses with nanoscale diameter can be achieved. We then fabricate lenses in gold ?lms and characterize their plasmonic properties using cathodoluminescence spectromicroscopy, demonstrating suitable plasmonic behavior for ultrafast nanoscale photoemission.
关键词： plasmonic lenses,cathodoluminescence spectromicroscopy,nanoscale,ultrafast electron emitters
更新于2025-09-11 14:15:04