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Nonlinear Optics || Ultrafast and Intense-Field Nonlinear Optics
摘要： There is currently great interest in the physics of ultrashort laser pulses. Recent advances have led to the generation of laser pulses with durations of the order of 1 attosecond (Hentschel et al., 2001). Ultrashort pulses can be used to probe the properties of matter on extremely short time scales. Within the context of nonlinear optics, ultrashort laser pulses are of interest for at least two separate reasons. The ?rst reason is that the nature of nonlinear optical interactions is often profoundly modi?ed through the use of ultrashort laser pulses, in part because of the broad spectral bandwidth necessarily associated with such pulses. The next two sections of this chapter treat various aspects of the resulting modi?cations of the nature of nonlinear optical interactions. The second reason is that ultrashort laser pulses tend to possess extremely high peak intensities (because laser pulse energies tend to be established by the energy-storage capabilities of laser gain media), and thus short laser pulses tend to have much higher peak powers than longer pulses. The second half of this chapter is devoted to a survey of the sorts of nonlinear optical processes that can be excited by extremely intense laser ?elds.
关键词： attosecond pulses,ultrashort laser pulses,high peak intensities,spectral bandwidth,nonlinear optics
更新于2025-09-23 15:21:01
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Investigation the effect of laser ablation parameters in a liquid in order to reduce the pulse energy during laser shock peening
摘要： The features of laser shock peening technology was studied in relation to the physical processes occurring during and after laser treatment. The effect of laser parameters on the results of the process was investigated. It was shown that the reduce of the diameter of the laser spot while maintaining the intensity leads to a decrease in the effect of LSP. This phenomenon was studied from the point of view of the features of plastic deformation at various sizes of the treatment zone using the standard model for the LSP process. Besides the features of the development of a plasma plume during laser ablation in a liquid are considered. It was shown that the liquid determines the geometry of the plume evolution and the shock wave caused by it. The process parameters used and the results obtained are important for the development of low-energy LSP technology.
关键词： Surface treatment,Laser shock peening,Laser-produced plasmas,Laser ablation in liquid,Nickel alloys,Laser pulses,Lasers
更新于2025-09-23 15:21:01
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Toward the laser control of electronic decoherence
摘要： Controlling electronic decoherence in molecules is an outstanding challenge in chemistry. Recent advances in the theory of electronic decoherence [B. Gu and I. Franco, J. Phys. Chem. Lett. 9, 773 (2018)] have demonstrated that it is possible to manipulate the rate of electronic coherence loss via control of the relative phase in the initial electronic superposition state. This control emerges when there are both relaxation and pure-dephasing channels for decoherence and applies to initially separable electron–nuclear states. In this paper, we demonstrate that (1) such an initial superposition state and the subsequent quantum control of electronic decoherence can be created via weak-field one-photon photoexcitation with few-cycle laser pulses of definite carrier envelope phase (CEP), provided the system is initially prepared in a separable electron–nuclear state. However, we also demonstrate that (2) when stationary molecular states (which are generally not separable) are considered, such one-photon laser control disappears. Remarkably, this happens even in situations in which the initially factorizable state is an excellent approximation to the stationary state with fidelity above 98.5%. The laser control that emerges for initially separable states is shown to arise because these states are superpositions of molecular eigenstates that open up CEP-controllable interference routes at the one-photon limit. Using these insights, we demonstrate that (3) the laser control of electronic decoherence from stationary states can be recovered by using a two-pulse control scheme, with the first pulse creating a vibronic superposition state and the second one inducing interference. This contribution advances a viable scheme for the laser control of electronic decoherence and exposes a surprising artifact that is introduced by widely used initially factorizable system-bath states in the field of open quantum systems.
关键词： electronic decoherence,few-cycle laser pulses,laser control,carrier envelope phase,vibronic superposition state,quantum control
更新于2025-09-23 15:21:01
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Generation of magnetic skyrmions by focused vortex laser pulses
摘要： We propose a method to generate magnetic skyrmions by intense laser pulses optimally focused on a magnetically ordered 2D-layer. In particular, we consider few-cycle intense pulses with the magnetic vortex structure near the focus region on the layer. The spin dynamics is modeled using the Landau–Lifshitz–Gilbert equation and includes the Dzyaloshinskii–Moriya interaction. We demonstrate that skyrmions can be observed within a few picoseconds after the end of the laser pulse. We analyze the physical picture of this process and work out which laser pulse and 2D-layer parameters are required for the generation.
关键词： Dzyaloshinskii–Moriya interaction,laser pulses,Landau–Lifshitz–Gilbert equation,magnetic skyrmions
更新于2025-09-23 15:21:01
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Numerical stability of time-dependent coupled-cluster methods for many-electron dynamics in intense laser pulses
摘要： We investigate the numerical stability of time-dependent coupled-cluster theory for many-electron dynamics in intense laser pulses, comparing two coupled-cluster formulations with full configuration interaction theory. Our numerical experiments show that orbital-adaptive time-dependent coupled-cluster doubles (OATDCCD) theory offers significantly improved stability compared with the conventional Hartree-Fock-based time-dependent coupled-cluster singles-and-doubles (TDCCSD) formulation. The improved stability stems from greatly reduced oscillations in the doubles amplitudes, which, in turn, can be traced to the dynamic biorthonormal reference determinants of OATDCCD theory. As long as these are good approximations to the Brueckner determinant, OATDCCD theory is numerically stable. We propose the reference weight as a diagnostic quantity to identify situations where the TDCCSD and OATDCCD theories become unstable.
关键词： time-dependent coupled-cluster theory,OATDCCD,Brueckner determinant,TDCCSD,intense laser pulses,numerical stability,many-electron dynamics
更新于2025-09-23 15:21:01
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<i>In situ</i> structural kinetics of picosecond laser-induced heating and fragmentation of colloidal gold spheres
摘要： Fragmentation of colloidal 54 nm gold nanoparticles by picosecond laser pulses is recorded by time-resolved X-ray scattering, giving access to structural dynamics down to a 80 ps resolution. Lattice temperature and energy dissipation have been quantified to verify that the maximum applied fluence of 1800 J m?2 heats up the particles close to boiling. Already within 30 ns, particles with significantly lower particle sizes of 2 to 3 nm are detected, which hints towards an ultrafast process either by a thermal phase explosion or Coulomb instability. An arrested growth is observed on a microsecond time scale resulting in a final particle size of 3–4 nm with high yield. In this context, the fragmentation in a NaCl/NaOH solution seems to limit growth by electrostatic stabilization of fragments, whereas it does not modify the initial product sizes. The laser-induced fragmentation process is identified as a single-step, instantaneous reaction.
关键词： Coulomb instability,fragmentation,thermal phase explosion,time-resolved X-ray scattering,picosecond laser pulses,gold nanoparticles
更新于2025-09-23 15:21:01
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Photoelectron Momentum Distributions of Single-Photon Ionization under a Pair of Elliptically Polarized Attosecond Laser Pulses
摘要： The attosecond ionization dynamics of atoms has attracted extensive attention during these days. However, the role of the initial state is not clearly understood. To address this question, we perform simulations on the neon atom and its model atom with different initial states by numerically solving the corresponding two-dimensional time-dependent Schr?dinger equations. We theoretically investigate atomic photoelectron momentum distributions (PMDs) by a pair of elliptically polarized attosecond laser pulses. We find that the PMD is sensitive not only to the ellipticities of the pulses, the relative helicity and time delay of the pulses, but also to the symmetry of the initial electronic states. Results are analyzed by the first-order time-dependent perturbation theory (TDPT) and offer a new tool for detecting the rotation direction of the ring currents.
关键词： photoelectron momentum distributions,elliptically polarized attosecond laser pulses,magnetic quantum numbers,the rotation direction of the ring currents
更新于2025-09-23 15:21:01
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exposed to an intense laser pulse
摘要： We investigate the role of the rotational excitation in the coherent and unidirectional B 2Σ+u emission of N2+ at 391 nm called air lasing generated when N2 is irradiated with intense femtosecond near-infrared laser pulses at 800 nm. We simulate the time-dependent population transfer process of N2+, which is assumed to be generated suddenly in an intense ultrashort laser pulse, by including vibrational and rotational degrees of freedom, and reveal that, when the light field intensity is below ≈ 4 × 1014 W cm?2, the population inversion can be achieved in N2+ only between rotationally highly excited levels in the vibrational ground (v' = 0) state of the B 2Σ+u state and those in the vibrational ground (v'' = 0) state of the electronic ground X 2Σ+g state, so that the lasing at 391 nm is realized even when the total population in the v' = 0 state of the electronically excited B 2Σ+u state is not inverted with respect to the total population in the v'' = 0 state of the electronic ground X 2Σ+g state.
关键词： air lasing,N2+,rotational excitation,population inversion,femtosecond laser pulses
更新于2025-09-23 15:21:01
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Ultrafast energy absorption and photoexcitation of bulk plasmon in crystalline silicon subjected to intense near-infrared ultrashort laser pulses
摘要： We investigate the non-linear response and energy absorption in bulk silicon irradiated by intense 12-fs near-infrared laser pulses. Depending on the laser intensity, we distinguish two regimes of non-linear absorption of the laser energy: for low intensities, energy deposition and photoionization involve perturbative three-photon transition through the direct bandgap of silicon. For laser intensities near and above 1014 W/cm2, corresponding to photocarrier density of order 1022 cm?3, we find that absorption at near-infrared wavelengths is greatly enhanced due to excitation of bulk plasmon resonance. In this regime, the energy transfer to electrons exceeds a few times the thermal melting threshold of Si. The optical reflectivity of the photoexcited solid is found in good qualitative agreement with existing experimental data. In particular, the model predicts that the main features of the reflectivity curve of photoexcited Si as a function of the laser fluence are determined by the competition between state and band filling associated with Pauli exclusion principle and Drude free-carrier response. The non-linear response of the photoexcited solid is also investigated for irradiation of silicon with a sequence of two strong and temporary non-overlapping pulses. The cumulative effect of the two pulses is non-additive in terms of deposited energy. Photoionization and energy absorption on the leading edge of the second pulse is greatly enhanced due to free carrier absorption.
关键词： bulk silicon,optical reflectivity,photoexcited solid,near-infrared laser pulses,Drude free-carrier response,non-linear response,energy absorption,plasmon resonance
更新于2025-09-23 15:21:01
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Transiently changing shape of the photon number distribution in a quantum-dota??cavity system driven by chirped laser pulses
摘要： We have simulated the time evolution of the photon number distribution in a semiconductor quantum-dot–microcavity system driven by chirped laser pulses and compare with unchirped results. When phonon interactions with the dot are disregarded—thus corresponding to the limit of atomic cavity systems—chirped pulses generate photon number distributions that change their shape drastically in the course of time. Phonons have a strong and qualitative impact on the photon statistics. The asymmetry between phonon absorption and emission destroys the symmetry of the photon distributions obtained for positive and negative chirps. While for negative chirps transient distributions resembling thermal ones are observed, for positive chirps the photon number distribution still resembles its phonon-free counterpart but with overall smoother shapes. In sharp contrast, using unchirped pulses of the same pulse area and duration wave packets are found that move up and down the Jaynes-Cummings ladder with a bell shape that changes little in time. For shorter pulses and lower driving strength Rabi-like oscillations occur between low photon number states. For all considered excitation conditions transitions between sub- and super-Poissonian statistics are found at certain times. For resonant driving with low intensity the Mandel parameter oscillates and is mostly negative, which indicates a nonclassical state in the cavity ?eld. Finally, we show that it is possible that the Mandel parameter dynamically approaches zero and still the photon distribution exhibits two maxima and thus is far from being a Poissonian.
关键词： Mandel parameter,photon number distribution,chirped laser pulses,quantum-dot–cavity system,phonon interactions
更新于2025-09-23 15:21:01