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Study of the parameter dependence of laser-accelerated protons from a hydrogen cluster source
摘要： We present a study on laser-driven proton acceleration from a hydrogen cluster target. Aiming for the optimisation of the proton source, we performed a detailed parametric scan of the interaction conditions by varying different laser and the target parameters. While the underlying process of a Coulomb-explosion delivers moderate energies, in the range of 100 s of keV, the use of hydrogen as target material comes with the bene?t of a debris-free, single-species proton acceleration scheme, enabling high repetition-rate experiments, which are very robust against shot-to-shot ?uctuations.
关键词： hydrogen cluster,coulomb-explosion,cryogenic target,laser-driven ion acceleration
更新于2025-09-23 15:21:01
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Direct imaging of direction-controlled molecular rotational wave packets created by a polarization-skewed double-pulse
摘要： High‐precision, time‐resolved Coulomb explosion imaging of rotational wave packets in nitrogen molecules created with a pair of time‐delayed, polarization‐skewed femtosecond laser pulses is presented, providing insight into creation process and dynamics of direction‐controlled wave packet. To initiate unidirectional rotation, the interval of the double‐pulse was set so that the second, polarization‐tilted pulse hit the molecules at the time when molecules were aligned or antialigned along the polarization vector of the first pulse. During the revival period of the rotational wave packet, pulse intervals around both the full and half revival times were used. The observed molecular wave packet movies clearly show signatures of quantum rotation such as angular localization (alignment), dispersion, and revival phenomena during the unidirectional motion. The patterns are quite different depending on the pulse interval even when angular distribution at the second pulse irradiation is similar. The observed interval‐dependence of the dynamics was analyzed on the basis of the real‐time images, with an aid of numerical simulations, and the creation process of the packets were discussed. We show the observed image patterns can be essentially rationalized in terms of rotational period and alignment parameter. Because the double‐pulse scheme is the most fundamental in the creation of direction‐controlled rotational wave packets, this study will lead to more sophisticated control and characterization of directional molecular motions.
关键词： rotational wave packets,Coulomb explosion imaging,quantum rotation,femtosecond laser pulses,unidirectional rotation
更新于2025-09-23 15:19:57
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Picosecond Laser-Induced Hierarchical Periodic Near- and Deep-Subwavelength Ripples on Stainless-Steel Surfaces
摘要： Ultrafast laser-induced periodic surface subwavelength ripples, categorized based on the ripple period into near-subwavelength ripples (NSRs) and deep-subwavelength ripples (DSRs), are increasingly found in the variety of materials such as metals, semiconductors and dielectrics. The fabrication of hierarchical periodic NSRs and DSRs on the same laser-irradiated area is still a challenge since the connection between the two remains a puzzle. Here we present an experimental study of linearly polarized picosecond laser-induced hierarchical periodic NSRs and DSRs on stainless-steel surfaces. While experiencing peak power density higher than a threshold value of 91.9 GW/cm2, in the laser-scanned area appear the hierarchical periodic NSRs and DSRs (in particular, the DSRs are vertically located in the valley of parallel NSRs). A large area of the uniformly hierarchical periodic NSRs and DSRs, with the spatial periods 356 ± 17 nm and 58 ± 15 nm, respectively, is fabricated by a set of optimized laser-scanning parameters. A qualitative explanation based on the surface plasmon polariton (SPP) modulated periodic coulomb explosion is proposed for unified interpretation of the formation mechanism of hierarchical periodic NSRs and DSRs, which includes lattice orientation of grains as a factor at low peak power density, so that the initial DSRs formed have a clear conformance with the metallic grains.
关键词： stainless steel,surface plasmon polaritons,coulomb explosion,laser induced subwavelength ripples
更新于2025-09-19 17:13:59
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BrCl <sup>+</sup> elimination from Coulomb explosion of 1,2-bromochloroethane induced by intense femtosecond laser fields
摘要： By using a dc-slice imaging technique, photodissociation of 1,2-C2H4BrCl was investigated at 800 nm looking for heteronuclear unimolecular ion elimination of BrCl+ in an 80 fs laser field. The occurrence of fragment ion BrCl+ in the mass spectrum verified the existence of a unimolecular decomposition channel of BrCl+ in this experiment. The relative quantum yield of the BrCl+ channel was measured to be 0.8%. By processing and analyzing the velocity and angular distributions obtained from the corresponding sliced images of BrCl+ and its partner ion C2H4+, we concluded that BrCl+ came from Coulomb explosion of the 1,2-bromochloroethane dication 1,2-C2H4BrCl2+. With the aid of quantum chemical calculations at the M06-2X/def2-TZVP level, the potential energy surface for BrCl+ detachment from 1,2-C2H4BrCl2+ has been examined in detail. According to the ab initio calculations, two transition state structures tended to correlate with the reactant 1,2-C2H4BrCl2+ and the products BrCl+ + C2H4+. In this entire dissociation process, the C–Br and C–Cl bond lengths were observed to elongate asymmetrically, that is, the C–Br chemical bond broke firstly, and subsequently a new Br–Cl chemical bond started to emerge while the C–Cl bond continued to exist for a while. Hence, an asynchronous concerted elimination mechanism was favored for BrCl+ detachment.
关键词： BrCl+ elimination,femtosecond laser,Coulomb explosion,photodissociation,asynchronous concerted mechanism
更新于2025-09-16 10:30:52
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Ultrafast electron transfer through silicon-vacuum interface induced by the action of intense femtosecond laser pulse
摘要： A theoretical study of the influence of a quasistationary electric field formed during emission separation of charges on ultrafast electron transfer near the silicon-vacuum interface irradiated by femtosecond laser pulses was carried out. The values of the strength of the arising quasistationary field during irradiation by femtosecond pulses with fluences near and above the silicon damage thresholds were estimated. The possibility of the formation of a dynamic optically layered structure in the near-surface layers of silicon irradiated by a femtosecond pulse resulting from a modification of its optical properties due to the depletion of electrons in the surface layer was studied. It is suggested that the time-depending dipole moment induced by the emission separation of charges should lead to the generation of electromagnetic radiation from the terahertz frequency range. The basic properties of this radiation were theoretically investigated.
关键词： Coulomb explosion,silicon,ultrafast heating,terahertz radiation,electron emission,electron transfer,femtosecond laser pulse
更新于2025-09-12 10:27:22
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A multihertz, kiloelectronvolt pulsed proton source from a laser irradiated continuous hydrogen cluster target
摘要： A high-repetition rate laser-driven proton source from a continuously operating cryogenic hydrogen cluster target is presented. We demonstrate a debris-free, Coulomb-explosion based acceleration in the 10s of kilo-electron-volt range with a stability of about 10% in a 5 Hz operation. This acceleration mechanism, delivering short pulse proton bursts, represents an ideal acceleration scheme for various applications, for example, in materials science or as an injector source in conventional accelerators. Furthermore, the proton energy can be tuned by varying the laser and/or cluster parameters. 3D numerical particle-in-cell simulations and an analytical model support the experimental results and reveal great potential for further studies, scaling up the proton energies, which can be realized with a simple modification of the target.
关键词： high-repetition rate,laser-driven proton source,Coulomb-explosion,particle-in-cell simulations,cryogenic hydrogen cluster target
更新于2025-09-11 14:15:04
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Coulomb explosion imaging of CH <sub/>3</sub> I and CH <sub/>2</sub> ClI photodissociation dynamics
摘要： The photodissociation dynamics of CH3I and CH2ClI at 272 nm were investigated by time-resolved Coulomb explosion imaging, with an intense non-resonant 815 nm probe pulse. Fragment ion momenta over a wide m/z range were recorded simultaneously by coupling a velocity map imaging spectrometer with a pixel imaging mass spectrometry camera. For both molecules, delay-dependent pump-probe features were assigned to ultraviolet-induced carbon-iodine bond cleavage followed by Coulomb explosion. Multi-mass imaging also allowed the sequential cleavage of both carbon-halogen bonds in CH2ClI to be investigated. Furthermore, delay-dependent relative fragment momenta of a pair of ions were directly determined using recoil-frame covariance analysis. These results are complementary to conventional velocity map imaging experiments and demonstrate the application of time-resolved Coulomb explosion imaging to photoinduced real-time molecular motion.
关键词： pixel imaging mass spectrometry,time-resolved,CH3I,velocity map imaging,photodissociation dynamics,Coulomb explosion imaging,CH2ClI
更新于2025-09-10 09:29:36