Publications
242 results found
Britton M, Lytova M, Laferriere P, et al., 2019, Short- and long-term gain dynamics in N-2(+) air lasing, PHYSICAL REVIEW A, Vol: 100, ISSN: 2469-9926
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- Citations: 13
Neufeld O, Ayuso D, Decleva P, et al., 2019, Ultrasensitive chiral spectroscopy by dynamical symmetry breaking in high harmonic generation, Physical Review X, Vol: 9, ISSN: 2160-3308
We propose and numerically demonstrate a new chiral spectroscopy method that is based on a universal system-independent mechanism of dynamical symmetry breaking in high harmonic generation (HHG). The proposed technique relies only on intense electric-dipole transitions and not on their interplay with magnetic dipole transitions. The symmetry breaking results in the emission of otherwise “forbidden” harmonics from chiral media (i.e., that are not emitted from achiral or racemic media), yielding a huge, nearly background-free, chiral-achiral signal that is correlated to the magnitude of the medium’s enantiomeric excess. The handedness of the medium can be directly detected by measuring the polarization helicity of the emitted harmonics. Moreover, the strength of the “allowed” harmonics (that are not related to symmetry breaking) is chirality independent; hence, they can be used as a reference to probe chiral degrees of freedom within a single measurement. We numerically demonstrate up to 99% chiral-achiral signal level (normalized difference between the chiral and achiral HHG spectra) from microscopic gas-phase emission using state-of-the-art models for HHG in bromochlorofluoromethane and propylene oxide. We expect the new method to give rise to precise tabletop characterization of chiral media in the gas phase and for highly sensitive time-resolved probing of dynamical chiral processes with femtosecond-to-attosecond temporal resolution.
Khokhlova MA, Cooper B, Ueda K, et al., 2019, Molecular Auger Interferometry, Physical Review Letters, Vol: 122, ISSN: 0031-9007
We introduce and present a theory of interferometric measurement of a normal Auger decay lifetime in molecules. Molecular Auger interferometry is based on the coherent phase control of Auger dynamics in a two-color (ω/2ω) laser field. We show that, in contrast to atoms, in oriented molecules of certain point groups the relative ω/2ω phase modulates the total ionization yield. A simple analytical formula is derived for the extraction of the lifetimes of Auger-active states from a molecular Auger interferogram, circumventing the need in either high-resolution or attosecond spectroscopy. We demonstrate the principle of the interferometric Auger lifetime measurement using inner-valence decay in CH3F.
Frolov MV, Manakov NL, Minina AA, et al., 2019, Analytic description of high-order harmonic generation in the adiabatic limit with application to an initial s state in an intense bicircular laser pulse, PHYSICAL REVIEW A, Vol: 99, ISSN: 2469-9926
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- Citations: 16
Dixit G, Jimenez-Galan A, Medisauskas L, et al., 2018, Control of the helicity of high-order harmonic radiation using bichromatic circularly polarized laser fields, PHYSICAL REVIEW A, Vol: 98, ISSN: 2469-9926
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- Citations: 18
Bello RY, Canton SE, Jelovina D, et al., 2018, Reconstruction of the time-dependent electronic wave packet arising from molecular autoionization, SCIENCE ADVANCES, Vol: 4, ISSN: 2375-2548
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- Citations: 11
Masin Z, Harvey AG, Spanner M, et al., 2018, Electron correlations and pre-collision in the re-collision picture of high harmonic generation, JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS, Vol: 51, ISSN: 0953-4075
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- Citations: 9
Matthews M, Morales F, Patas A, et al., 2018, Amplification of intense light fields by nearly free electrons (vol 14, pg 695, 2018), NATURE PHYSICS, Vol: 14, Pages: 767-767, ISSN: 1745-2473
Frolov MV, Manakov NL, Minina AA, et al., 2018, Control of harmonic generation by the time delay between two-color, bicircular few-cycle mid-IR laser pulses, Physical Review Letters, Vol: 120, Pages: 1-6, ISSN: 0031-9007
We study control of high-order harmonic generation (HHG) driven by time-delayed, few-cycle ω and 2ω counterrotating mid-IR pulses. Our numerical and analytical study shows that the time delay between the two-color pulses allows control of the harmonic positions, both those allowed by angular momentum conservation and those seemingly forbidden by it. Moreover, the helicity of any particular harmonic is tunable from left to right circular without changing the driving pulse helicity. The highest HHG yield occurs for a time delay comparable to the fundamental period T=2π/ω.
Pisanty E, Hickstein DD, Galloway BR, et al., 2018, High harmonic interferometry of the Lorentz force in strong mid-infrared laser fields, New Journal of Physics, Vol: 20, ISSN: 1367-2630
The interaction of intense mid-infrared laser fields with atoms and moleculesleads to a range of new opportunities, from the production of bright, coherentradiation in the soft x-ray range to imaging molecular structures and dynamicswith attosecond temporal and sub-angstrom spatial resolution. However, allthese effects, which rely on laser-driven recollision of an electron removed bythe strong laser field and the parent ion, suffer from the rapidly increasingrole of the magnetic field component of the driving pulse: the associatedLorentz force pushes the electrons off course in their excursion and suppressesall recollision-based processes, including high harmonic generation, elasticand inelastic scattering. Here we show how the use of two non-collinear beamswith opposite circular polarizations produces a forwards ellipticity which canbe used to monitor, control, and cancel the effect of the Lorentz force. Thisarrangement can thus be used to re-enable recollision-based phenomena inregimes beyond the long-wavelength breakdown of the dipole approximation, andit can be used to observe this breakdown in high-harmonic generation usingcurrently-available light sources.
Matthews M, Morales F, Patas A, et al., 2018, Amplification of intense light fields by nearly free electrons, Nature Physics, Vol: 14, Pages: 695-700, ISSN: 1745-2473
Light can be used to modify and control properties of media, as in the case of electromagnetically induced transparency or, more recently, for the generation of slow light or bright coherent extreme ultraviolet and X-ray radiation. Particularly unusual states of matter can be created by light fields with strengths comparable to the Coulomb field that binds valence electrons in atoms, leading to nearly free electrons oscillating in the laser field and yet still loosely bound to the core1,2. These are known as Kramers–Henneberger states3, a specific example of laser-dressed states2. Here, we demonstrate that these states arise not only in isolated atoms4,5, but also in rare gases, at and above atmospheric pressure, where they can act as a gain medium during laser filamentation. Using shaped laser pulses, gain in these states is achieved within just a few cycles of the guided field. The corresponding lasing emission is a signature of population inversion in these states and of their stability against ionization. Our work demonstrates that these unusual states of neutral atoms can be exploited to create a general ultrafast gain mechanism during laser filamentation.
Jimenez-Galan A, Dixit G, Patchkovskii S, et al., 2018, Attosecond recorder of the polarization state of light, NATURE COMMUNICATIONS, Vol: 9, ISSN: 2041-1723
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- Citations: 9
Jimenez-Galan A, Zhavoronkov N, Schloz M, et al., 2017, Time-resolved high harmonic spectroscopy of dynamical symmetry breaking in bi-circular laser fields: the role of Rydberg states, OPTICS EXPRESS, Vol: 25, Pages: 22880-22896, ISSN: 1094-4087
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- Citations: 27
Medisauskas L, Bello RY, Palacios A, et al., 2017, A molecular clock for autoionization decay, JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS, Vol: 50, ISSN: 0953-4075
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- Citations: 1
Bredtmann T, Patchkovskii S, Ivanov MY, 2017, Strong-field assisted extreme-ultraviolet lasing in atoms and molecules, NEW JOURNAL OF PHYSICS, Vol: 19, ISSN: 1367-2630
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- Citations: 5
Ayuso D, Jimenez-Galan A, Morales F, et al., 2017, Attosecond control of spin polarization in electron-ion recollision driven by intense tailored fields, NEW JOURNAL OF PHYSICS, Vol: 19, ISSN: 1367-2630
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- Citations: 29
Richter M, Morales F, Spanner M, et al., 2017, Optical Lasing during Laser Filamentation in the Nitrogen Molecular Ion: Ro-Vibrational Inversion, Conference on Lasers and Electro-Optics Europe / European Quantum Electronics Conference (CLEO/Europe-EQEC), Publisher: IEEE
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- Citations: 4
Ayuso D, Jimenez-Galan A, Morales F, et al., 2017, Attosecond control of spin polarization in electron-ion recollision driven by intense tailored fields, Conference on Lasers and Electro-Optics Europe / European Quantum Electronics Conference (CLEO/Europe-EQEC), Publisher: IEEE
Jimenez-Galan A, Dixit G, Patchkovskii S, et al., 2017, Characterization of attosecond pulses of arbitrary polarization, Conference on Lasers and Electro-Optics Europe / European Quantum Electronics Conference (CLEO/Europe-EQEC), Publisher: IEEE
Silva REF, Blinov IV, Rubtsov AN, et al., 2017, High harmonic generation spectroscopy of laser induced phase transitions in strongly correlated systems, Conference on Lasers and Electro-Optics Europe / European Quantum Electronics Conference (CLEO/Europe-EQEC), Publisher: IEEE
Schuette B, Ye P, Patchkovskii S, et al., 2016, Strong-field ionization of clusters using two-cycle pulses at 1.8 μm, Scientific Reports, Vol: 6, ISSN: 2045-2322
The interaction of intense laser pulses with nanoscale particles leads to the production of high-energy electrons, ions, neutral atoms, neutrons and photons. Up to now, investigations have focused on near-infrared to X-ray laser pulses consisting of many optical cycles. Here we study strong-field ionization of rare-gas clusters (103 to 105 atoms) using two-cycle 1.8 μm laser pulses to access a new interaction regime in the limit where the electron dynamics are dominated by the laser field and the cluster atoms do not have time to move significantly. The emission of fast electrons with kinetic energies exceeding 3 keV is observed using laser pulses with a wavelength of 1.8 μm and an intensity of 1 × 1015 W/cm2, whereas only electrons below 500 eV are observed at 800 nm using a similar intensity and pulse duration. Fast electrons are preferentially emitted along the laser polarization direction, showing that they are driven out from the cluster by the laser field. In addition to direct electron emission, an electron rescattering plateau is observed. Scaling to even longer wavelengths is expected to result in a highly directional current of energetic electrons on a few-femtosecond timescale.
Austin DR, McGrath F, Miseikis L, et al., 2016, Role of tunnel ionization in high harmonic generation from substituted benzenes., Faraday Discussions, Vol: 194, Pages: 349-368, ISSN: 1364-5498
We theoretically study high-harmonic generation in toluene, ortho-xylene and fluorobenzene driven by a 1.8 μm ultrashort pulse. We find that the chemical substitutions have a strong influence on the amplitude and phase of the emission from the highest occupied molecular orbital, despite having a small influence on the orbital itself. We show that this influence is due to the tunnel ionization step, which depends critically on the sign and amplitude of the asymptotic part of the wave function. We discuss how these effects would manifest in phase-sensitive high-harmonic generation spectroscopy experiments.
Milne CJ, Weber PM, Kowalewski M, et al., 2016, Attosecond processes and X-ray spectroscopy: general discussion, Faraday Discussions, Vol: 194, Pages: 427-462, ISSN: 1359-6640
Pisanty Alatorre E, Ivanov M, 2016, Kinematic origin for near-zero energy structures in mid-IR strong field ionization, Journal of Physics B - Atomic Molecular and Optical Physics, Vol: 49, ISSN: 0953-4075
We propose and discuss a kinematic mechanism underlying the recently discovered ‘Near-Zero Energy Structure’ in the photoionization of atoms in strong mid-infrared laser fields, based on trajectories which revisit the ion at low velocities exactly analogous to the series responsible for the Low-Energy Structures. The different scaling of the new series, as E ∼ I_p^2/U_p , suggests that the Near-Zero Energy Structure can be lifted to higher energies, where it can be better resolved and studied, using harder targets with higher ionization potential.
Pisanty E, Ivanov M, 2016, Slalom in complex time: emergence of low-energy structures in tunnel ionization via complex time contours, Physical Review A, Vol: 93, ISSN: 1094-1622
The ionization of atoms by strong, low-frequency fields can generally bedescribed well by assuming that the photoelectron is, after the ionizationstep, completely at the mercy of the laser field. However, certain phenomena,like the recent discovery of low-energy structures in the long-wavelengthregime, require the inclusion of the Coulomb interaction with the ion once theelectron is in the continuum. We explore the first-principles inclusion of thisinteraction, known as analytical R-matrix theory, and its consequences on thecorresponding quantum orbits. We show that the trajectory must have animaginary component, and that this causes branch cuts in the complex time planewhen the real trajectory revisits the neighbourhood of the ionic core. Weprovide a framework for consistently navigating these branch cuts based onclosest-approach times, which satisfy the equation $\mathbf{r}(t) \cdot\mathbf{v}(t) = 0$ in the complex plane. We explore the geometry of these rootsand describe the geometrical structures underlying the emergence of LES in boththe classical and quantum domains.
Bredtmann T, Chelkowski S, Bandrauk AD, et al., 2016, XUV lasing during strong-field-assisted transient absorption in molecules, Physical Review A, Vol: 93, ISSN: 1094-1622
Using ab initio non-Born-Oppenheimer simulations, we demonstrate the amplification of XUV radiation in a high-harmonic-generation-type process using the example of the hydrogen molecular ion. A small fraction of the molecules is pumped to a dissociative excited state from which IR-assisted XUV amplification is observed. We show that starting at sufficiently high IR driving field intensities, the ground-state molecules become quasitransparent for XUV radiation, while due to stabilization, gain from excited states is maintained. While the basic physics should also be observable in atomic media, the main advantage of the investigated molecular laser is, first, efficient lasing from field-free excited states with a high mean angular momentum and, second, the possibility to tune the amplified XUV frequency windows via control of the internuclear distance.
Kaushal J, Morales F, Torlina L, et al., 2015, Spin-orbit Larmor clock for ionization times in one-photon and strong-field regimes, Journal of Physics B-Atomic Molecular and Optical Physics, Vol: 48, ISSN: 1361-6455
Photoionization is a process where absorption of one or several photons liberates an electron and creates a hole in a quantum system, such as an atom or a molecule. Is it faster to remove an electron using one or many photons, and how to define this time? Here we introduce a clock that allows us to define ionization time for both one-photon and many-photon ionization regimes. The clock uses the interaction of the electron or hole spin with the magnetic field created by their orbital motion, known as the spin–orbit interaction. The angle of spin precession in the magnetic field records time. We use the combination of analytical theory and ab initio calculations to show how ionization delay depends on the number of absorbed photons, how it appears in the experiment and what electron dynamics it signifies. In particular, we apply our method to calculate the derived time delays in tunneling regime of strong-field ionization.
Richter M, Bouakline F, Gonzalez-Vazquez J, et al., 2015, Sub-laser-cycle control of coupled electron-nuclear dynamics at a conical intersection, New Journal of Physics, Vol: 17, ISSN: 1367-2630
Nonadiabatic processes play a fundamental role in the understanding of photochemical processes in excited polyatomic molecules. A particularly important example is that of radiationless electronic relaxation at conical intersections (CIs). We discuss new opportunities for controlling coupled electron–nuclear dynamics at CIs, offered by the advent of nearly single-cycle, phase-stable, mid-infrared laser pulses. To illustrate the control mechanism, a two-dimensional model of the NO2 molecule is considered. The key idea of the control scheme is to match the time scale of the laser field oscillations to the characteristic time scale of the wave packet transit through the CI. The instantaneous laser field changes the shape and position of the CI as the wave packet passes through. As the CI moves in the laser field, it 'slices' through the wave packet, sculpting it in the coordinate and momentum space in a way that is sensitive to the carrier-envelope phase of the control pulse. We find that the electronic coherence imparted on the sub-laser-cycle time scale manifests during much longer nuclear dynamics that follow on the many tens of femtosecond time scale. Control efficiency as a function of molecular orientation is analyzed, showing that modest alignment is sufficient for showing the described effects.
Medisauskas L, Patchkovskii S, Harvey A, et al., 2015, Initial electronic coherence in molecular dissociation induced by an attosecond pulse, Physical Review A, Vol: 92, ISSN: 1094-1622
We investigate the influence of the attosecond electron dynamics of photoionization on the femtosecond fragmentation of the molecular ion left behind. We consider the dissociative photoionization dynamics of the N2 molecule, induced by an attosecond extreme-ultraviolet (XUV) pulse in the presence of a moderately strong infrared (IR) laser field. We show that the kinetic energy spectrum of N+ fragments depends on (i) the phases between the different electronic states of N2+ established by the photoionization process and (ii) phases associated with the vibrational dynamics in the dissociating molecular ion. We show that the phase acquired during the photoionization can be obtained from the dependence of the N+ ion kinetic energy release spectra on the time delay between the XUV and IR pulses.
Medisauskas L, Wragg J, van der Hart H, et al., 2015, Generating isolated elliptically polarized attosecond pulses using bichromatic counterrotating circularly polarized laser fields, Physical Review Letters, Vol: 115, ISSN: 1079-7114
We theoretically demonstrate the possibility to generate both trains and isolated attosecond pulses with high ellipticity in a practical experimental setup. The scheme uses circularly polarized, counterrotating two-color driving pulses carried at the fundamental and its second harmonic. Using a model Ne atom, we numerically show that highly elliptic attosecond pulses are generated already at the single-atom level. Isolated pulses are produced by using few-cycle drivers with controlled time delay between them.
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