Showing papers on "High harmonic generation published in 2007"
TL;DR: In this paper, the performance of a free-electron laser operating at a wavelength of 13.7 nm where unprecedented peak and average powers for a coherent extreme-ultraviolet radiation source have been measured.
Abstract: We report results on the performance of a free-electron laser operating at a wavelength of 13.7 nm where unprecedented peak and average powers for a coherent extreme-ultraviolet radiation source have been measured. In the saturation regime, the peak energy approached 170 J for individual pulses, and the average energy per pulse reached 70 J. The pulse duration was in the region of 10 fs, and peak powers of 10 GW were achieved. At a pulse repetition frequency of 700 pulses per second, the average extreme-ultraviolet power reached 20 mW. The output beam also contained a significant contribution from odd harmonics of approximately 0.6% and 0.03% for the 3rd (4.6 nm) and the 5th (2.75 nm) harmonics, respectively. At 2.75 nm the 5th harmonic of the radiation reaches deep into the water window, a wavelength range that is crucially important for the investigation of biological samples.
1,390 citations
TL;DR: In this article, the authors present the landmarks of the 10-odd-year progress in this field, focusing on the theoretical modeling of the propagation equations, whose physical ingredients are discussed from numerical simulations.
Abstract: Modern laser sources nowadays deliver ultrashort light pulses reaching few cycles in duration and peak powers exceeding several terawatt (TW). When such pulses propagate through optically transparent media, they first self-focus in space and grow in intensity, until they generate a tenuous plasma by photo-ionization. For free electron densities and beam intensities below their breakdown limits, these pulses evolve as self-guided objects, resulting from successive equilibria between the Kerr focusing process, the chromatic dispersion of the medium and the defocusing action of the electron plasma. Discovered one decade ago, this self-channeling mechanism reveals a new physics, widely extending the frontiers of nonlinear optics. Implications include long-distance propagation of TW beams in the atmosphere, supercontinuum emission, pulse shortening as well as high-order harmonic generation. This review presents the landmarks of the 10-odd-year progress in this field. Particular emphasis is laid on the theoretical modeling of the propagation equations, whose physical ingredients are discussed from numerical simulations. The dynamics of single filaments created over laboratory scales in various materials such as noble gases, liquids and dielectrics reveal new perspectives in pulse shortening techniques. Far-field spectra provide promising diagnostics. Attention is also paid to the multifilamentation instability of broad beams, breaking up the energy distribution into small-scale cells along the optical path. The robustness of the resulting filaments in adverse weathers, their large conical emission exploited for multipollutant remote sensing, nonlinear spectroscopy and the possibility of guiding electric discharges in air are finally addressed on the basis of experimental results.
858 citations
TL;DR: An ultrabroad extreme ultraviolet supercontinuum spectrum with a 148 eV spectral width can be generated which directly creates an isolated 65 as pulse even without phase compensation, and is explained by analyzing maximum electron kinetic energies at different return times.
Abstract: We theoretically investigate the high-order harmonic generation in a helium atom with a two-color optical field synthesized by an intense 6 fs pulse at 800 nm and a relatively weak 21.3 fs pulse at 400 nm. When the frequency-doubled pulse is properly time shifted with respect to the fundamental pulse, an ultrabroad extreme ultraviolet supercontinuum spectrum with a 148 eV spectral width can be generated which directly creates an isolated 65 as pulse even without phase compensation. We explain this extraordinary phenomenon by analyzing maximum electron kinetic energies at different return times.
259 citations
TL;DR: Quasi-phase matching and quantum path control of high-harmonic generation using counterpropagating light using counter-propagation light are discussed in this article. But this work is restricted to the case of high harmonic generation.
Abstract: Quasi-phase-matching and quantum-path control of high-harmonic generation using counterpropagating light
226 citations
TL;DR: The first evidence of x-ray harmonic radiation extending to 3.3 A, 3.8 keV (order n>3200) from petawatt class laser-solid interactions is presented, exhibiting relativistic limit efficiency scaling at multi-keV energies.
Abstract: The first evidence of x-ray harmonic radiation extending to 3.3 A, 3.8 keV (order n > 3200) from petawatt class laser-solid interactions is presented, exhibiting relativistic limit efficiency scaling (eta similar to n(-2.5)-n(-3)) at multi-keV energies. This scaling holds up to a maximum order, n(RO)similar to 8(1/2)gamma(3), where gamma is the relativistic Lorentz factor, above which the first evidence of an intensity dependent efficiency rollover is observed. The coherent nature of the generated harmonics is demonstrated by the highly directional beamed emission, which for photon energy h nu > 1 keV is found to be into a cone angle similar to 4 degrees, significantly less than that of the incident laser cone (20 degrees).
206 citations
TL;DR: Self-phase-stabilized near-IR pulses have been generated by difference-frequency generation of a filament broadened supercontinuum followed by two-stage optical parametric amplification, suited as a driver for high-order harmonic generation and isolated attosecond pulse production.
Abstract: Ultrabroadband self-phase-stabilized near-IR pulses have been generated by difference-frequency generation of a filament broadened supercontinuum followed by two-stage optical parametric amplification. Pulses with energy up to 1.2 mJ and duration down to 17 fs are demonstrated. These characteristics make such a source suited as a driver for high-order harmonic generation and isolated attosecond pulse production.
185 citations
TL;DR: In this article, coherent superposition of laser-driven soft-X-ray (SXR) harmonics, at wavelengths of 2-5nm, generated in two successive sources by one and the same laser pulse is reported.
Abstract: High-order harmonic generation from atoms ionized by femtosecond laser pulses has been a promising approach for the development of coherent short-wavelength sources. However, the realization of a powerful harmonic X-ray source has been hampered by a phase velocity mismatch between the driving wave and its harmonics, limiting their coherent build-up to a short propagation length and thereby compromising the efficiency of a single source. Here, we report coherent superposition of laser-driven soft-X-ray (SXR) harmonics, at wavelengths of 2–5 nm, generated in two successive sources by one and the same laser pulse. Observation of constructive and destructive interference suggests the feasibility of quasi-phase-matched SXR harmonic generation by a focused laser beam in a gas medium of modulated density. Our proof-of-concept study opens the prospect of enhancing the photon flux of SXR harmonic sources to levels enabling researchers to tackle a range of applications in physical as well as life sciences.
179 citations
TL;DR: General conditions for 100% frequency conversion in any doubly resonant nonlinear cavity, for both second- and third-harmonic generation via Chi?((2))and Chi((3)) nonlinearities are derived.
Abstract: We derive general conditions for 100% frequency conversion in any doubly resonant nonlinear cavity, for both second- and third-harmonic generation via χ(2) and χ(3) nonlinearities. We find that conversion efficiency is optimized for a certain “critical” power depending on the cavity parameters, and assuming reasonable parameters we predict 100% conversion using milliwatts of power or less. These results follow from a semi-analytical coupled-mode theory framework which is generalized from previous work to include both χ(2) and χ(3) media as well as inhomogeneous (fully vectorial) cavities, analyzed in the high-efficiency limit where down-conversion processes lead to a maximum efficiency at the critical power, and which is verified by direct finite-difference time-domain (FDTD) simulations of the nonlinear Maxwell equations. Explicit formulas for the nonlinear coupling coefficients are derived in terms of the linear cavity eigenmodes, which can be used to design and evaluate cavities in arbitrary geometries.
156 citations
TL;DR: In this article, the role of surface plasmon in second harmonic generation from arrays of gold nanorod particles excited by femtosecond laser pulses is investigated as a function of incident light polarization and irradiation wavelength.
Abstract: The role of surface plasmon in second harmonic generation from arrays of gold nanorod particles excited by femtosecond laser pulses is investigated as a function of incident light polarization and irradiation wavelength. In addition to photoluminescence, a peak of second harmonic is observed and is found to depend on the polarization and wavelength of the fundamental frequency laser beam. In particular, the authors found similarities between extinction spectra of the nanoparticles and spectra of emmitted second harmonic. This behavior can be explained by resonant excitation of localized surface plasmon resonances.
135 citations
TL;DR: In this article, a review of studies of high-order harmonic generation in plasma plumes is presented, where the generation of highorder harmonics (up to the 101st order, λ = 7.9 nm) of Ti:sapphire laser radiation during the propagation of short laser pulses through a low-excited, low-ionized plasma produced on the surfaces of different targets is analyzed.
Abstract: A review of studies of high-order harmonic generation in plasma plumes is presented. The generation of high-order harmonics (up to the 101st order, λ = 7.9 nm) of Ti:sapphire laser radiation during the propagation of short laser pulses through a low-excited, low-ionized plasma produced on the surfaces of different targets is analysed. The observation of considerable resonance-induced enhancement of a single harmonic (λ = 61.2 nm) at the plateau region with 10−4 conversion efficiency in the case of an In plume can offer some expectations that analogous processes can be realized in other plasma samples in the shorter wavelength range. Recent achievements of single-harmonic enhancement at mid- and end-plateau regions are discussed. Various methods for the optimization of harmonic generation are analysed, such as the application of the second harmonic of driving radiation and the application of prepulses of different durations. The enhancement of harmonic generation efficiency during the propagation of femtosecond pulses through a nanoparticle-containing plasma is discussed.
128 citations
TL;DR: It is shown that the polarization of the extreme ultraviolet emission depends strongly on the molecular alignment and the orbital structure, and molecular alignment will allow us to produce attosecond pulses with time-dependent polarization.
Abstract: High harmonic emission in isotropic gases is polarized in the same direction as the incident laser polarization. Laser-induced molecular alignment allows us to break the symmetry of the gas medium. By using aligned molecules in high harmonic generation experiments, we show that the polarization of the extreme ultraviolet emission depends strongly on the molecular alignment and the orbital structure. Polarization measurements give insight into the molecular orbital symmetry. Furthermore, molecular alignment will allow us to produce attosecond pulses with time-dependent polarization.
Patent•
26 Oct 2007
TL;DR: In this article, linear conductors sized to correspond to the light wavelengths are used to rectify an alternating waveform induced upon the conductors by the lightwave electromagnetic energy, which is effective to produce harmonic energy at light wavelengths.
Abstract: An optical antenna collects, modifies and emits energy at light wavelengths. Linear conductors sized to correspond to the light wavelengths are used. Nonlinear junctions of small dimension are used to rectify an alternating waveform induced upon the conductors by the lightwave electromagnetic energy. The optical antenna and junctions are effective to produce harmonic energy at light wavelengths. The linear conductors may be comprised of carbon nanotubes that are attached to a substrate material, which may then be connected to an electrical port.
TL;DR: In this article, the authors derived general conditions for 100 percent frequency conversion in any doubly resonant nonlinear cavity, for both second and third-harmonic generation via chi2 and chi3 nonlinearities.
Abstract: We derive general conditions for 100 percent frequency conversion in any doubly resonant nonlinear cavity, for both second- and third-harmonic generation via chi2 and chi3 nonlinearities. We find that conversion efficiency is optimized for a certain critical power depending on the cavity parameters, and assuming reasonable parameters we predict 100 percent conversion using milliwatts of power or less. These results follow from a semi-analytical coupled-mode theory framework which is generalized from previous work to include both chi2 and chi3 media as well as inhomogeneous (fully vectorial) cavities, analyzed in the high-efficiency limit where down-conversion processes lead to a maximum efficiency at the critical power, and which is verified by direct finite-difference time-domain (FDTD) simulations of the nonlinear Maxwell equations. Explicit formulas for the nonlinear coupling coefficients are derived in terms of the linear cavity eigenmodes, which can be used to design and evaluate cavities in arbitrary geometries.
TL;DR: This work investigates the fundamental-wavelength dependence of high-harmonic generation yield and finds surprisingly strong and rapid fluctuations on a fine wavelength scale, due to quantum-path interferences.
Abstract: We investigate the dependence of the intensity of radiation due to high-harmonic generation as a function of the wavelength $\ensuremath{\lambda}$ of the fundamental driver field. Superimposed on a smooth power-law dependence observed previously, we find surprisingly strong and rapid fluctuations on a fine $\ensuremath{\lambda}$ scale. We identify the origin of these fluctuations in terms of quantum path interferences with up to five returning orbits significantly contributing.
TL;DR: The dominance of the dramatic enhancement effect is supported by simulation with the time-dependent Schrödinger equation as well as the observed spatial characteristic of the generated harmonics and dependence on medium conditions.
Abstract: We present a dramatic enhancement [Phys. Rev. Lett. 91, 043002 (2003)] of high-order harmonic generation by simultaneous irradiation of booster harmonics. A key feature of our experiment is the use of mixed gases (Xe and He) with different ionization energies. The harmonics from Xe atoms act as a booster to increase the harmonic yield from He by a factor of $4\ifmmode\times\else\texttimes\fi{}{10}^{3}$. The dominance of the dramatic enhancement effect is supported by simulation with the time-dependent Schr\"odinger equation as well as the observed spatial characteristic of the generated harmonics and dependence on medium conditions.
TL;DR: Experiments and computer simulations on the generation of high order harmonics from steep plasma gradients using intense femtosecond laser pulses make it possible to clearly distinguish between nonrelativistic and relativistic mechanisms of harmonic generation.
Abstract: Experiments and computer simulations on the generation of high order harmonics from steep plasma gradients using intense femtosecond laser pulses are presented. Qualitative changes in the harmonic emission take place when the intensities are increased above 10(19) W/cm2 and/or the plasma scale length is varied. Good agreement between experimental and calculated spectra makes it possible to clearly distinguish between nonrelativistic and relativistic mechanisms of harmonic generation.
TL;DR: Generalized envelope equation simulations are shown to be in excellent quantitative agreement with the numerical integration of Maxwell's equations, even in the presence of shock dynamics and carrier steepening on a sub-50 attosecond timescale.
Abstract: We describe generalized nonlinear envelope equation modeling of sub-cycle dynamics on the underlying electric field carrier during one-dimensional propagation in fused silica. Generalized envelope equation simulations are shown to be in excellent quantitative agreement with the numerical integration of Maxwell's equations, even in the presence of shock dynamics and carrier steepening on a sub-50 attosecond timescale. In addition, by separating the effects of self-phase modulation and third harmonic generation, we examine the relative contribution of these effects in supercontinuum generation in fused silica nanowire waveguides.
17 Jun 2007
TL;DR: High-order harmonic emission is observed in acetylene and allene molecules with 14 fs laser pulses producing a time dependent modulation of the harmonic signal as the ensemble undergoes the subsequent alignment revivals.
Abstract: Laser driven high-order harmonic generation (HHG) from molecules depends on the particular symmetry of the highest occupied molecular orbital (HOMO) and its orientation with respect to the laser field. High-order harmonic emission is observed in acetylene and allene molecules with 14 fs laser pulses. The molecules are aligned non-adiabatically producing a time dependent modulation of the harmonic signal as the ensemble undergoes the subsequent alignment revivals. At the points of maximum alignment the harmonic signal is measured as a function of the alignment angle showing a behavior that can be related to the structure of the highest occupied molecular orbitals.
06 May 2007
TL;DR: In this article, the relativistic third-harmonic generation by using a periodic plasma waveguide is achieved, and the resonance dependence of harmonic intensity on plasma density modulation parameters is observed.
Abstract: Enhancement of relativistic third-harmonic generation by using a periodic plasma waveguide is achieved. Resonant dependence of harmonic intensity on plasma density modulation parameters is observed, which is a distinct characteristic of quasi-phase matching.
TL;DR: In this article, the authors proposed a method to detect the presence of a cancer in the human brain using the chemical sciences, geosciences and biosciences division of the Office of Basic Energy Sciences (OES).
Abstract: This work was supported in part by the Chemical Sciences,
Geosciences and Biosciences Division of the Office of
Basic Energy Sciences, Office of Science, U.S. Department
of Energy, and by NSF.
TL;DR: In this paper, it was shown that the number of attosecond pulses and their intensities can be controlled by either the relative phase between the two color fields or the carrier-envelope phase.
Abstract: Numerical simulations have revealed that by adding a second harmonic field to a laser field with a time-dependent ellipticity, single isolated attosecond pulses can be generated as a result of the combined power of the two-color gating and the polarization gating. The duration of the pump laser applicable to this double optical gating scheme is a factor of 2 longer than that for the conventional polarization gating. Pulses with 200 attosecond duration can be generated from argon gas even with $10\phantom{\rule{0.3em}{0ex}}\mathrm{fs}$ lasers. It was discovered that the number of attosecond pulses and their intensities could be controlled by either the relative phase between the two color fields or the carrier-envelope phase.
TL;DR: Multimodal multiphoton microscopy using HHGM together with two‐photon excited fluorescence will develop into a key approach to real‐time imaging of cell dynamics in the context of live tissues.
Abstract: Multiphoton microscopy has become a standard method for noninvasive imaging of thick specimens with subcellular resolution. Higher harmonic generation microscopy (HHGM), based on nonlinear multiphoton excitation, is a contrast mechanism for the structural and molecular imaging of native samples in cell culture and in fixed and live tissues, for both, three-dimensional and four-dimensional reconstructions. HHGM comprises second and third harmonic generation (SHG, THG) of ordered molecules, can be obtained without exogenous labels, and provides detailed real-time optical reconstruction of fibrillar collagen, myosin, microtubules, and membrane potential, as well as cell depolarization. This unit presents the principles of SHG and THG and the basic setup of a HHGM system, and summarizes current applications in cell biology. Multimodal multiphoton microscopy using HHGM together with two-photon excited fluorescence will develop into a key approach to real-time imaging of cell dynamics in the context of live tissues.
TL;DR: An original ab initio Maxwell–Schrodinger model and a methodology to simulate intense ultrashort laser pulses interacting with a 3D H + -gas in the nonlinear nonperturbative regime under and beyond Born–Oppenheimer approximation are presented.
TL;DR: In this article, the ellipticity dependence of high-order harmonic generation (HHG) from aligned N2, O2, and CO2 molecules has been investigated and shown to be sensitive to molecular alignment and the shape and symmetry of the valence orbitals.
Abstract: We report ellipticity dependence of high-order harmonic generation (HHG) from aligned N2, O2, and CO2 molecules. Experimentally, we find that the ellipticity dependence is sensitive to molecular alignment and to the shape and symmetry of the valence orbitals. It is also found that the destructive interference in the recombination process affects the ellipticity dependence. Theoretically, we extend the original Lewenstein model to a more generalized model, which can be applicable to HHG from molecules, by introducing an electron acceleration parameter xi(theta) and by combining the molecular orbital method. The present observations are successfully explained by our model.
TL;DR: The amplitude of the continuum electron wave packet versus kinetic energy is derived and is shown to be largely independent of the atom, in agreement with models of tunnel ionization.
Abstract: High harmonic spectra were recorded from different rare-gas atoms under identical experimental conditions. It is shown that although each atom's spectrum is different, the differences are due almost entirely to the orbital influence in the recombination step. The amplitude of the continuum electron wave packet versus kinetic energy is derived from these data and is shown to be largely independent of the atom, in agreement with models of tunnel ionization. We compare the measurements with calculations in both the length gauge and the velocity gauge and show that the two gauges imply a different de Broglie wavelength.
Journal Article•
TL;DR: In this article, the effects of laser beam quality and linewidth on the second-harmonic generation efficiency were investigated using a Yb-doped fiber laser, and a quasiphase matching in periodically poled Mgdoped stoichiometric lithium tantalate at room temperature was achieved.
Abstract: Single-pass second-harmonic generation of 7W continuous wave of 542nm radiation with 35.4% efficiency was achieved by quasiphase matching in periodically poled Mg-doped stoichiometric lithium tantalate at room temperature. The effects of laser beam quality and linewidth on the second-harmonic generation efficiency were investigated using a Yb-doped fiber laser.
TL;DR: Temporal characterization of the harmonic pulses has been obtained using cross-correlation method: pulses as short as 8 fs, with high photon flux, have been measured at the output of the monochromator.
Abstract: Extreme-ultraviolet pulses, produced by high-order harmonic generation, have been spectrally selected by a time-delay-compensated grating monochromator. Temporal characterization of the harmonic pulses has been obtained using cross-correlation method: pulses as short as 8 fs, with high photon flux, have been measured at the output of the monochromator.
TL;DR: In this paper, femtosecond time-resolved dynamic Gabor holography using highly coherent extreme ultraviolet light generated by high harmonic upconversion of a femto-cond laser was demonstrated.
Abstract: We demonstrate femtosecond time-resolved dynamic Gabor holography using highly coherent extreme ultraviolet light generated by high harmonic upconversion of a femtosecond laser. By reflecting this light from an impulsively heated surface, we implement a simple and robust single-reflection geometry for phase-sensitive holographic detection at extreme UV wavelengths. Using this setup, we study the ultrafast deformation and subsequent acoustic oscillations within a thin metal film. These measurements exhibit subpicometer spatial sensitivity in the vertical dimension.
TL;DR: This work reports on the first experimental evidence of the destructive and constructive interference of high harmonics generated in a mixed gas of He and Ne, which offers a novel method for coherent control of high harmonic generation, measuring harmonic phases, and observing the underlying attosecond electron dynamics.
Abstract: We report on the first experimental evidence of the destructive and constructive interference of high harmonics generated in a mixed gas of He and Ne, which facilitates the coherent control of high harmonic generation. Theoretically, we develop an analytical model of high harmonic generation in mixed gases and succeed in reproducing the experimental results and deriving the optimization conditions for the process. The observed interference modulation is attributed to the difference between the phases of the intrinsically chirped harmonic pulses from He and Ne, which leads to a novel method for broadband measurement of the harmonic phases and for observing the underlying attosecond electron dynamics.