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Author

Shunsuke A. Sato

Bio: Shunsuke A. Sato is an academic researcher from University of Tsukuba. The author has contributed to research in topics: Attosecond & Physics. The author has an hindex of 21, co-authored 92 publications receiving 1915 citations. Previous affiliations of Shunsuke A. Sato include Max Planck Society & Applied Science Private University.

Papers published on a yearly basis

Papers
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Journal ArticleDOI
12 Dec 2014-Science
TL;DR: Attosecond extreme ultraviolet (XUV) spectroscopy is used to resolve the electron transfer from valence to conduction band states in semiconductors, and distinguished the electron dynamics—which proceed faster than a quadrillionth of a second after laser excitation—from the comparatively slower lattice motion of the silicon atomic nuclei.
Abstract: Electron transfer from valence to conduction band states in semiconductors is the basis of modern electronics. Here, attosecond extreme ultraviolet (XUV) spectroscopy is used to resolve this process in silicon in real time. Electrons injected into the conduction band by few-cycle laser pulses alter the silicon XUV absorption spectrum in sharp steps synchronized with the laser electric field oscillations. The observed ~450-attosecond step rise time provides an upper limit for the carrier-induced band-gap reduction and the electron-electron scattering time in the conduction band. This electronic response is separated from the subsequent band-gap modifications due to lattice motion, which occurs on a time scale of 60 ± 10 femtoseconds, characteristic of the fastest optical phonon. Quantum dynamical simulations interpret the carrier injection step as light-field–induced electron tunneling.

444 citations

Journal ArticleDOI
TL;DR: The Octopus project as mentioned in this paper provides a unique framework that allows us to describe non-equilibrium phenomena in molecular complexes, low dimensional materials, and extended systems by accounting for electronic, ionic, and photon quantum mechanical effects within a generalized time-dependent density functional theory.
Abstract: Over the last few years, extraordinary advances in experimental and theoretical tools have allowed us to monitor and control matter at short time and atomic scales with a high degree of precision. An appealing and challenging route toward engineering materials with tailored properties is to find ways to design or selectively manipulate materials, especially at the quantum level. To this end, having a state-of-the-art ab initio computer simulation tool that enables a reliable and accurate simulation of light-induced changes in the physical and chemical properties of complex systems is of utmost importance. The first principles real-space-based Octopus project was born with that idea in mind, i.e., to provide a unique framework that allows us to describe non-equilibrium phenomena in molecular complexes, low dimensional materials, and extended systems by accounting for electronic, ionic, and photon quantum mechanical effects within a generalized time-dependent density functional theory. This article aims to present the new features that have been implemented over the last few years, including technical developments related to performance and massive parallelism. We also describe the major theoretical developments to address ultrafast light-driven processes, such as the new theoretical framework of quantum electrodynamics density-functional formalism for the description of novel light-matter hybrid states. Those advances, and others being released soon as part of the Octopus package, will allow the scientific community to simulate and characterize spatial and time-resolved spectroscopies, ultrafast phenomena in molecules and materials, and new emergent states of matter (quantum electrodynamical-materials).

215 citations

Journal ArticleDOI
26 Aug 2016-Science
TL;DR: Attosecond transient absorption spectroscopy was applied to investigate the interaction between polycrystalline diamond and a few-femtosecond infrared pulse with intensity below the critical intensity of optical breakdown, and identified infrared induction of intraband currents as the main physical mechanism responsible for the observations.
Abstract: Short, intense laser pulses can be used to access the transition regime between classical and quantum optical responses in dielectrics. In this regime, the relative roles of inter- and intraband light-driven electronic transitions remain uncertain. We applied attosecond transient absorption spectroscopy to investigate the interaction between polycrystalline diamond and a few-femtosecond infrared pulse with intensity below the critical intensity of optical breakdown. Ab initio time-dependent density functional theory calculations, in tandem with a two-band parabolic model, accounted for the experimental results in the framework of the dynamical Franz-Keldysh effect and identified infrared induction of intraband currents as the main physical mechanism responsible for the observations.

212 citations

Journal ArticleDOI
02 Jun 2016-Nature
TL;DR: It is demonstrated that attosecond metrology extends the resolution to petahertz frequencies of visible light and Quantitative determination of dissipation within a signal manipulation cycle of only a few femtoseconds duration reveals the feasibility of dielectric optical switching at clock rates above 100 teraherz.
Abstract: Petahertz-bandwidth metrology is demonstrated in the measurement of nonlinear polarization in silica. Recent years have seen an increased interest in light–matter interactions in solid-state systems at ultrafast timescales. Ferenc Krausz and colleagues study the nonlinear polarization of silica in response to intense infrared light fields with a spectroscopy method in the attosecond time range. The method makes it possible to unravel details of the reversible and irreversible energy exchange between infrared light and electrons and points to the feasibility of using light-based switching techniques for signal processing in solid-state devices above 100 terahertz. Electric-field-induced charge separation (polarization) is the most fundamental manifestation of the interaction of light with matter and a phenomenon of great technological relevance. Nonlinear optical polarization1,2 produces coherent radiation in spectral ranges inaccessible by lasers and constitutes the key to ultimate-speed signal manipulation. Terahertz techniques3,4,5,6,7,8 have provided experimental access to this important observable up to frequencies of several terahertz9,10,11,12,13. Here we demonstrate that attosecond metrology14 extends the resolution to petahertz frequencies of visible light. Attosecond polarization spectroscopy allows measurement of the response of the electronic system of silica to strong (more than one volt per angstrom) few-cycle optical (about 750 nanometres) fields. Our proof-of-concept study provides time-resolved insight into the attosecond nonlinear polarization and the light–matter energy transfer dynamics behind the optical Kerr effect and multi-photon absorption. Timing the nonlinear polarization relative to the driving laser electric field with sub-30-attosecond accuracy yields direct quantitative access to both the reversible and irreversible energy exchange between visible–infrared light and electrons. Quantitative determination of dissipation within a signal manipulation cycle of only a few femtoseconds duration (by measurement and ab initio calculation) reveals the feasibility of dielectric optical switching at clock rates above 100 terahertz. The observed sub-femtosecond rise of energy transfer from the field to the material (for a peak electric field strength exceeding 2.5 volts per angstrom) in turn indicates the viability of petahertz-bandwidth metrology with a solid-state device.

197 citations

Journal ArticleDOI
TL;DR: In this article, a multiscale simulation of solid-state high-order-harmonic generation was performed for dielectrics and it was shown that mesoscopic effects of the extended system, in particular the realistic sampling of the entire Brillouin zone, the pulse propagation in the dense medium, and the inhomogeneous illumination of the crystal, have a strong effect on the harmonic spectra.
Abstract: High-order-harmonic generation by a highly nonlinear interaction of infrared laser fields with matter allows for the generation of attosecond pulses in the XUV spectral regime This process, well established for atoms, has been recently extended to the condensed phase Remarkably well-pronounced harmonics up to order $\ensuremath{\sim}30$ have been observed for dielectrics We establish a route toward an ab initio multiscale simulation of solid-state high-order-harmonic generation We find that mesoscopic effects of the extended system, in particular the realistic sampling of the entire Brillouin zone, the pulse propagation in the dense medium, and the inhomogeneous illumination of the crystal, have a strong effect on the harmonic spectra Our results provide an explanation for the formation of clean harmonics and have implications for a wide range of nonlinear optical processes in dense media

149 citations


Cited by
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Journal ArticleDOI
TL;DR: In this article, the time dependence of ρ11, ρ22 and ρ12 under steady-state conditions was analyzed under a light field interaction V = -μ12Ee iωt + c.c.
Abstract: (b) Write out the equations for the time dependence of ρ11, ρ22, ρ12 and ρ21 assuming that a light field interaction V = -μ12Ee iωt + c.c. couples only levels |1> and |2>, and that the excited levels exhibit spontaneous decay. (8 marks) (c) Under steady-state conditions, find the ratio of populations in states |2> and |3>. (3 marks) (d) Find the slowly varying amplitude ̃ ρ 12 of the polarization ρ12 = ̃ ρ 12e iωt . (6 marks) (e) In the limiting case that no decay is possible from intermediate level |3>, what is the ground state population ρ11(∞)? (2 marks) 2. (15 marks total) In a 2-level atom system subjected to a strong field, dressed states are created in the form |D1(n)> = sin θ |1,n> + cos θ |2,n-1> |D2(n)> = cos θ |1,n> sin θ |2,n-1>

1,872 citations

Book
01 Jan 2010

1,870 citations

Book
30 Apr 2020
TL;DR: In this paper, the fundamental properties of soft x-rays and extreme ultraviolet (EUV) radiation are discussed and their applications in a wide variety of fields, including EUV lithography for semiconductor chip manufacture and soft X-ray biomicroscopy.
Abstract: This self-contained, comprehensive book describes the fundamental properties of soft x-rays and extreme ultraviolet (EUV) radiation and discusses their applications in a wide variety of fields, including EUV lithography for semiconductor chip manufacture and soft x-ray biomicroscopy. The author begins by presenting the relevant basic principles such as radiation and scattering, wave propagation, diffraction, and coherence. He then goes on to examine a broad range of phenomena and applications. The topics covered include EUV lithography, biomicroscopy, spectromicroscopy, EUV astronomy, synchrotron radiation, and soft x-ray lasers. He also provides a great deal of useful reference material such as electron binding energies, characteristic emission lines and photo-absorption cross-sections. The book will be of great interest to graduate students and researchers in engineering, physics, chemistry, and the life sciences. It will also appeal to practicing engineers involved in semiconductor fabrication and materials science.

786 citations

Journal ArticleDOI
25 Jun 2015-Nature
TL;DR: It is found that solid-state high harmonics are perturbed by fields so weak that they are present in conventional electronic circuits, thus opening a route to integrate electronics with attosecond and high-harmonic technology.
Abstract: When intense light interacts with an atomic gas, recollision between an ionizing electron and its parent ion creates high-order harmonics of the fundamental laser frequency. This sub-cycle effect generates coherent soft X-rays and attosecond pulses, and provides a means to image molecular orbitals. Recently, high harmonics have been generated from bulk crystals, but what mechanism dominates the emission remains uncertain. To resolve this issue, we adapt measurement methods from gas-phase research to solid zinc oxide driven by mid-infrared laser fields of 0.25 volts per angstrom. We find that when we alter the generation process with a second-harmonic beam, the modified harmonic spectrum bears the signature of a generalized recollision between an electron and its associated hole. In addition, we find that solid-state high harmonics are perturbed by fields so weak that they are present in conventional electronic circuits, thus opening a route to integrate electronics with attosecond and high-harmonic technology. Future experiments will permit the band structure of a solid to be tomographically reconstructed.

572 citations