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Attosecond Pulse Shaping by Multilayer Mirrors
摘要： The emerging research field of attosecond science allows for the temporal investigation of one of the fastest dynamics in nature: electron dynamics in matter. These dynamics are responsible for chemical and biological processes, and the ability to understand and control them opens a new door of fundamental science, with the possibility to influence all lives if medical issues can thereby be addressed. Multilayer optics are key elements in attosecond experiments; they are used to tailor attosecond pulses with well-defined characteristics to facilitate detailed and accurate insight into processes, e.g., photoemission, Auger decay, or (core-) excitons. Based on the investigations and research efforts from the past several years, multilayer mirrors today are routinely used optical elements in attosecond beamlines. As a consequence, the generation of ultrashort pulses, combined with their dispersion control, has proceeded from the femtosecond range in the visible/infrared spectra to the attosecond range, covering the extreme ultraviolet and soft X-ray photon range up to the water window. This article reviews our work on multilayer optics over the past several years, as well as the impact from other research groups, to reflect on the scientific background of their nowadays routine use in attosecond physics.
关键词： attosecond,X-ray,extreme ultraviolet (EUV),soft X-ray,multilayer,mirror
更新于2025-09-23 15:23:52
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Characterizing the ellipticity of an isolated attosecond pulse
摘要： We propose and theoretically demonstrate a single-shot measurement method to measure the ellipticity of an isolated attosecond pulse (IAP). By solving the time-dependent Schr?dinger equation, we calculate the photoelectron momentum distributions (PMDs) from strong field ionization of argon in an arbitrary polarized IAP streaked with a linearly polarized infrared pulse. It is shown that the ellipticity of the IAP is encoded in the PMDs. A linear relation between the angular shift of the three main lobes of the PMDs and the ellipticity of the IAP is obtained, which provides an efficient and robust way for characterizing the ellipticity of the IAP.
关键词： Photoelectron momentum distribution,Attosecond pulse,Elliptically polarized
更新于2025-09-23 15:23:52
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Attosecond pulse generation via multicolor beam superposition in the over-barrier ionization regime
摘要： Based on coherent superposition of multicolor continuous wave beams, high order harmonics and attosecond pulse generation from a hydrogen molecular ion (HMI), +H ,2 with different internuclear distances, R, are studied. Driving pulse intensity was taken to be 400 TW cm?2, which can ionize an +H2 ion with R?>?Rb?=?2.4 a.u. over the barrier. It is seen that cutoff harmonic with respect to R decreases until the over barrier ionization threshold, Rb, then becomes almost uniform to the end of R?=?10 a.u. whereas it is almost constant with respect to the spectral width of the beams, Δω. Besides attosecond pulse intensity increases versus R, and decreases with respect to Δω so that the most intense attosecond pulses can be generated from HMIs with R???5 a.u. via the pulses by Δω???0.03 a.u. Attosecond pulse durations were insensitive to both Δω and R.
关键词： hydrogen ion molecule,high order harmonic generation,H2,attosecond
更新于2025-09-23 15:21:21
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Enhancement of attosecond pulse in water window region by using pump-probe approach
摘要： An effective scheme to enhance the harmonic yield and the attosecond (as) pulse signal from H+2 has been proposed by using the pump-probe laser field. It is found that with the help of the multi-cycle pump pulse, H+2 can be steered into the resonance ionization regions, where the ionization probability can be remarkably enhanced. Thus, the harmonic yield can be remarkably enhanced when a sequential mid-infrared probe pulse is added. Further, by modulating the phase of the probe pulse and by adding a controlling pulse, the harmonic cutoff can be extended up to the water window region. Finally, by the Fourier transformation of the selected harmonics on the harmonic supercontinuum, the water window attosecond pulses as short as 25 as can be obtained.
关键词： High-order harmonic generation,pump-probe pulse,charge resonance enhanced ionization,single attosecond pulse,harmonic enhancement
更新于2025-09-23 15:21:21
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Ellipticity control of high-order harmonic generation with nearly orthogonal two-color laser fields
摘要： Elliptically polarized high-order harmonics opens a path toward the study of ultrafast dynamics in circular dichroism of magnetic materials, chiral molecules, and electronic spin motion. Recently, efficient high-order harmonic generation with controllable ellipticity has attracted considerable attention in experiment and theory. Here, we experimentally demonstrate a scenario using cross-linearly-polarized two-color fields consisting of a fundamental field and its second harmonic (SH). Through adjusting the relative phase, crossing angle, and intensity ratio of the cross-linearly-polarized two-color field, we obtain ellipticity-tunable high-order harmonics, with ellipticity up to ε = 0.73. Meanwhile, the elliptically polarized high-order harmonics preserve high efficiency. Furthermore, when the intensity of the SH field is stronger than that of the fundamental field, the even order harmonics will become several times stronger than the odd order harmonics with opposite helicity.
关键词： attosecond science,high-order harmonic generation,ellipticity control,strong-field physics,two-color laser fields
更新于2025-09-23 15:21:01
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Intense circularly polarized attosecond pulse generation from solid targets irradiated with a two-color linearly polarized laser
摘要： A method for the production of intense circularly polarized (CP) attosecond pulses from relativistic laser-solid interactions is proposed, where a two-color linearly polarized (LP) laser is used. The polarization, photon frequency, and other properties of the obtained attosecond pulse can be controlled by adjusting the ratio of the dichromatic driving LP field in different harmonics, which is much easier and more efficient than those previously using CP driving lasers. Both one- and two-dimensional particle-in-cell simulations show that a CP attosecond extreme-ultraviolet pulse with an intensity of 1.4 × 1019 W/cm2 and a duration of about 120 as is obtained by a two-color LP laser at intensities in the fundamental and second harmonics of, respectively, 1.5 × 1022 and 6.4 × 1021 W/cm2, which can be applied for the detection of the magnetic and chiral properties of materials.
关键词： relativistic laser-solid interactions,attosecond pulse,two-color linearly polarized laser,circularly polarized,extreme-ultraviolet pulse
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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Attosecond transient-absorption spectroscopy of polar molecules
摘要： We apply attosecond transient absorption spectroscopy (ATAS) to explore the effects of a nonzero permanent dipole on electron dynamics at the subfemtosecond scale, exemplified in the polar LiF molecule. In contrast with nonpolar systems, a familiar feature of the ATA spectra—the light-induced structures—are observed adjacent to a bright state. Moreover, a previously unobserved ladder structure is identified. The observations are analyzed in the context of a model based on fixed-nuclei adiabatic states, supported by full numerical simulations. Analytic calculations originating in the adiabatic model shed light on the nature and origins of the findings.
关键词： LiF molecule,attosecond transient absorption spectroscopy,electron dynamics,polar molecules,ladder structure,light-induced structures
更新于2025-09-23 15:21:01
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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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A pump-probe scheme with a single chirped pulse to image electron and nuclear dynamics in molecules
摘要： A single chirped few-femtosecond pulse can be used to control and image coupled electron-nuclear dynamics. Using full ab initio simulations of the simplest molecule, H+2, as a prototype target, we show that for intermediate values of the chirp, interference between sequential and direct contributions enables significant control over ionization yields, even when taking into account the effective decoherence introduced by nuclear motion and the presence of an electronic continuum. For larger values of the chirp, the single chirped pulse reproduces a classical pump-probe setup, with the chirp parameter mapping an effective time delay between the pumping and probing frequencies of the pulse. After demonstrating this numerically, we present a full analytical solution for the two-photon ionization amplitudes that provides an intuitive analogy between the molecular dynamics induced by a single chirped pulse and a traditional pump-probe setup.
关键词： pump-probe scheme,attosecond science,chirped pulse,molecular ionization,electron-nuclear dynamics
更新于2025-09-23 15:21:01