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George N. Gibson

Bio: George N. Gibson is an academic researcher from University of Connecticut. The author has contributed to research in topics: Ionization & Excited state. The author has an hindex of 28, co-authored 115 publications receiving 3867 citations. Previous affiliations of George N. Gibson include University of Illinois at Urbana–Champaign & Université de Sherbrooke.


Papers
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Journal ArticleDOI
TL;DR: In this article, electron correlations in a direct nonlinear process of inner-shell excitation were found to be important in multielectron processes, leading to evidence for a role of electron correlation in the nonlinear processes of inner shell excitation.
Abstract: Measurements of the vacuum-ultraviolet (<80-nm) radiation produced by intense ultraviolet (248-nm) irradiation (1015–1016 W/cm2) of rare gases have revealed the copious presence of both harmonic radiation and fluorescence from excited levels. The highest harmonic observed was the seventeenth (14.6 nm) in Ne, the shortest wavelength ever produced by that means. Strong fluorescence was seen from ions of Ar, Kr, and Xe, with the shortest wavelengths observed being below 12 nm. Furthermore, radiation from inner-shell excited configurations in Xe, specifically the 4d95s5p → 4d105s manifold of Xe7+ at ~17.7 nm, was detected. These experimental findings, in alliance with other studies concerning multielectron processes, give evidence for a role of electron correlations in a direct nonlinear process of inner-shell excitation.

1,409 citations

Journal ArticleDOI
TL;DR: In this article, strong-field single ionization and double ionization of two diatomic molecules were studied and compared to Xe and Ar, using an intense ultrashort pulse Ti:sapphire laser in the $2.5 to $8.5 GHz range.
Abstract: Strong-field single ionization and double ionization of two diatomic molecules, ${\mathrm{O}}_{2}$ and ${\mathrm{N}}_{2},$ are studied and compared to Xe and Ar, using an intense ultrashort pulse Ti:sapphire laser in the $2\ifmmode\times\else\texttimes\fi{}{10}^{13}$ to $8\ifmmode\times\else\texttimes\fi{}{10}^{14}{\mathrm{W}/\mathrm{c}\mathrm{m}}^{2}$ intensity range. ${\mathrm{N}}_{2}$ behaves like a structureless atom for both single and double ionization. The recently reported suppression of the ${\mathrm{O}}_{2}^{+}$ ion yield compared to ${\mathrm{Xe}}^{+}$ is confirmed in our experiment, but we show that the suppression is not due to dissociative recombination. Rather, we conclude that the ionization rate of ${\mathrm{O}}_{2}$ is below that predicted by tunneling ionization. We extend the study to the double ionization of ${\mathrm{O}}_{2}$ and find a distinctly reduced nonsequential double-ionization rate. We find evidence that electronic structure influences strong-field tunneling ionization in molecules.

276 citations

Journal ArticleDOI
TL;DR: In this paper, the optical breakdown threshold (OBT) in dielectrics with different band gaps was measured for single and double 25-fs 800-nm transform-limited laser pulses.
Abstract: We measured the optical breakdown threshold (OBT) in dielectrics with different band gaps for single and double 25-fs 800-nm transform-limited laser pulses. Our pump-probe double pulse measurements indicate that the plasma energy in dielectrics experiences ultrafast decay which lasts only $\ensuremath{\sim}100\mathrm{fs}$ and does not follow an exponential decay curve. Therefore, a decay term must be included in the electron density rate equation. Our double pulse measurements also demonstrate that the OBT is temperature dependent. The OBT in dielectrics was determined using a novel technique, which eliminates the ambiguity in its definition and also allows real-time data acquisition.

214 citations

Journal ArticleDOI
TL;DR: This work presents the results of an ultrafast, time-resolved spectroscopic investigation of a series of open-chain carotenoids derived from photosynthetic bacteria and systematically increasing in their number of pi-electron carbon-carbon double bonds, and proposes that in polar solvents, the ground state of spirilloxanthin takes on a corkscrew conformation that generates a net solute dipole moment while decreasing the cavity formation energy.
Abstract: Many of the spectroscopic features and photophysical properties of carotenoids are explained using a three-state model in which the strong visible absorption of the molecules is associated with an S0 (11 ) → S2 (11 ) transition, and the lowest lying singlet state, S1 (21 ), is a state into which absorption from the ground state is forbidden by symmetry. However, semiempirical and ab initio quantum calculations have suggested additional excited singlet states may lie either between or in the vicinity of S1 (21 ) and S2 (11 ), and some ultrafast spectroscopic studies have reported evidence for these states. One such state, denoted S*, has been implicated as an intermediate in the depopulation of S2 (11 ) and as a pathway for the formation of carotenoid triplet states in light-harvesting complexes. In this work, we present the results of an ultrafast, time-resolved spectroscopic investigation of a series of open-chain carotenoids derived from photosynthetic bacteria and systematically increasing in their num...

141 citations

Journal ArticleDOI
02 Jun 1996
TL;DR: In this paper, the authors proposed a cavity-dumping scheme for short-pulse Ti:sapphire laser with a single-Pulse energy of 62 nJ, where the AO wave must traverse the beam waist in the round-trip time of the cavity, limiting the energy to roughly 30 /spl mu/m.
Abstract: Summary form only given. Acousto-optical cavity-dumping (AO) has been demonstrated with short-pulse Ti:sapphire lasers producing single-pulse energies of 62 nJ. However, AO cavity-dumping is inherently limited because the AO wave must traverse the beam waist in the round-trip time of the cavity limiting the beam waist to roughly 30 /spl mu/m. This limits the pulse energy as the intensity must be kept below the threshold for nonlinear processes in the AO crystal. Furthermore, the contrast in the pulse energy on either side of the main cavity-dumped pulse is rather low (30:1 or 20:1). Electro-optical (EO) cavity dumping has no such limitation and can be scaled to higher energies with high contrast. However, there are several difficulties associated with EO cavity dumping all of which have now been solved.

119 citations


Cited by
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Journal ArticleDOI
TL;DR: In this article, the authors present the landmarks of the 30-odd-year evolution of ultrashort-pulse laser physics and technology culminating in the generation of intense few-cycle light pulses and discuss the impact of these pulses on high-field physics.
Abstract: The rise time of intense radiation determines the maximum field strength atoms can be exposed to before their polarizability dramatically drops due to the detachment of an outer electron. Recent progress in ultrafast optics has allowed the generation of ultraintense light pulses comprising merely a few field oscillation cycles. The arising intensity gradient allows electrons to survive in their bound atomic state up to external field strengths many times higher than the binding Coulomb field and gives rise to ionization rates comparable to the light frequency, resulting in a significant extension of the frontiers of nonlinear optics and (nonrelativistic) high-field physics. Implications include the generation of coherent harmonic radiation up to kiloelectronvolt photon energies and control of the atomic dipole moment on a subfemtosecond $(1{\mathrm{f}\mathrm{s}=10}^{\mathrm{\ensuremath{-}}15}\mathrm{}\mathrm{s})$ time scale. This review presents the landmarks of the 30-odd-year evolution of ultrashort-pulse laser physics and technology culminating in the generation of intense few-cycle light pulses and discusses the impact of these pulses on high-field physics. Particular emphasis is placed on high-order harmonic emission and single subfemtosecond extreme ultraviolet/x-ray pulse generation. These as well as other strong-field processes are governed directly by the electric-field evolution, and hence their full control requires access to the (absolute) phase of the light carrier. We shall discuss routes to its determination and control, which will, for the first time, allow access to the electromagnetic fields in light waves and control of high-field interactions with never-before-achieved precision.

2,547 citations

Journal ArticleDOI
TL;DR: In this paper, the main aspects of ultrashort laser pulse filamentation in various transparent media such as air (gases), transparent solids and liquids are introduced and discussed.

2,282 citations

Proceedings Article
Ferenc Krausz1
01 Aug 2007
TL;DR: In this paper, an attosecond "oscilloscope" was used to visualize the oscillating electric field of visible light with an oscillator and probe multi-electron dynamics in atoms, molecules and solids.
Abstract: Summary form only given. Fundamental processes in atoms, molecules, as well as condensed matter are triggered or mediated by the motion of electrons inside or between atoms. Electronic dynamics on atomic length scales tends to unfold within tens to thousands of attoseconds (1 attosecond [as] = 10-18 s). Recent breakthroughs in laser science are now opening the door to watching and controlling these hitherto inaccessible microscopic dynamics. The key to accessing the attosecond time domain is the control of the electric field of (visible) light, which varies its strength and direction within less than a femtosecond (1 femtosecond = 1000 attoseconds). Atoms exposed to a few oscillations cycles of intense laser light are able to emit a single extreme ultraviolet (XUV) burst lasting less than one femtosecond. Full control of the evolution of the electromagnetic field in laser pulses comprising a few wave cycles have recently allowed the reproducible generation and measurement of isolated sub-femtosecond XUV pulses, demonstrating the control of microscopic processes (electron motion and photon emission) on an attosecond time scale. These tools have enabled us to visualize the oscillating electric field of visible light with an attosecond "oscilloscope", to control single-electron and probe multi-electron dynamics in atoms, molecules and solids. Recent experiments hold promise for the development of an attosecond X-ray source, which may pave the way towards 4D electron imaging with sub-atomic resolution in space and time.

1,618 citations

Journal ArticleDOI
TL;DR: In this paper, a number of consequences of relativistic-strength optical fields are surveyed, including wakefield generation, a relativistically version of optical rectification, in which longitudinal field effects could be as large as the transverse ones.
Abstract: The advent of ultraintense laser pulses generated by the technique of chirped pulse amplification (CPA) along with the development of high-fluence laser materials has opened up an entirely new field of optics. The electromagnetic field intensities produced by these techniques, in excess of ${10}^{18}\phantom{\rule{0.3em}{0ex}}\mathrm{W}∕{\mathrm{cm}}^{2}$, lead to relativistic electron motion in the laser field. The CPA method is reviewed and the future growth of laser technique is discussed, including the prospect of generating the ultimate power of a zettawatt. A number of consequences of relativistic-strength optical fields are surveyed. In contrast to the nonrelativistic regime, these laser fields are capable of moving matter more effectively, including motion in the direction of laser propagation. One of the consequences of this is wakefield generation, a relativistic version of optical rectification, in which longitudinal field effects could be as large as the transverse ones. In addition to this, other effects may occur, including relativistic focusing, relativistic transparency, nonlinear modulation and multiple harmonic generation, and strong coupling to matter and other fields (such as high-frequency radiation). A proper utilization of these phenomena and effects leads to the new technology of relativistic engineering, in which light-matter interactions in the relativistic regime drives the development of laser-driven accelerator science. A number of significant applications are reviewed, including the fast ignition of an inertially confined fusion target by short-pulsed laser energy and potential sources of energetic particles (electrons, protons, other ions, positrons, pions, etc.). The coupling of an intense laser field to matter also has implications for the study of the highest energies in astrophysics, such as ultrahigh-energy cosmic rays, with energies in excess of ${10}^{20}\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. The laser fields can be so intense as to make the accelerating field large enough for general relativistic effects (via the equivalence principle) to be examined in the laboratory. It will also enable one to access the nonlinear regime of quantum electrodynamics, where the effects of radiative damping are no longer negligible. Furthermore, when the fields are close to the Schwinger value, the vacuum can behave like a nonlinear medium in much the same way as ordinary dielectric matter expanded to laser radiation in the early days of laser research.

1,459 citations