We demonstrate a technique that uses high-order harmonic generation in molecules to probe nuclear dynamics and structural rearrangement on subfemtosecond time scale. The chirped nature of the electron wavepacket produced by laser ionization strong field gives rise similar chirp photons emitted upon electron-ion recombination. Use this light allows information about be gained with 100-attosecond temporal resolution, from excitation an 8-femtosecond pulse, single shot. Measurements molecular...

We report a new dynamic two-center interference effect in high-harmonic generation from ${\mathrm{H}}_{2}$, which the attosecond nuclear motion of ${\mathrm{H}}_{2}^{+}$ initiated at ionization causes to be observed lower harmonic orders than would case for static nuclei. To enable this measurement we utilize recently developed technique probing dynamics small molecules. The experimental results are reproduced by theoretical analysis based upon strong-field approximation incorporates...

We calculate the emission times of radiation in high-order harmonic generation using Gabor transform numerical data obtained from solving time-dependent Schr\"odinger equation one, two, and three dimensions. Both atomic molecular systems, including nuclear motion, are investigated. Lewenstein model calculations used to gauge performance method. The resulting compared against classical simple man's as well more accurate quantum orbit based on complex trajectories. influence range binding...

The generation of high-order harmonics in diatomic molecules is investigated within the framework strong-field approximation. We show that conventional saddle-point approximation not suitable for large internuclear distances. An adapted method takes into account molecular structure presented. analyze predictions harmonic-generation spectra both velocity and length gauges. At separations, we compare resulting cutoffs with three-step semiclassical mechanism. Good agreement obtained only by...

The influence of the magnetic-field component incident pulse on emission photons by multiply charged ions interacting with intense, near-infrared laser pulses is investigated theoretically using a strong-field approximation that treats coupling atom field beyond dipole approximation. For peak intensities approaching ${10}^{17}{\mathrm{W}\mathrm{}\mathrm{cm}}^{\ensuremath{-}2},$ electron drift in propagation direction due to strongly influences photon spectra. In particular, reduced and...

We investigate the influence of Coulombic nature binding potential on high-order harmonic generation in ${\mathrm{H}}_{2}^{+}$ molecules. show that two-center interference effects are predicted accurately using approximated Coulomb wave functions for electron continuum state recombination amplitude determines probability emission upon recollision.

The low-energy end of the spectrum photoelectrons detached from hydrogenic ions exposed to an intense low-frequency few-cycle pulse is calculated within strong-field approximation (SFA). effect on photoelectron Coulomb field nucleus taken into account quasiclassically. results are compared with those ab initio solution time-dependent Schr\"odinger equation, for case ${\mathrm{He}}^{+}$ ion irradiated by a $400\text{\ensuremath{-}}\mathrm{nm}$...

Recently, a method to image molecular electronic orbitals using high-order harmonic generation was introduced by Itatani et al. [Nature 432, 876 (2004)]. We show that, while the tomographic reconstruction of general with arbitrary symmetry cannot be performed long laser pulses, this becomes possible when extremely short pulses are used. This statement is shown both in simplified wave-packet picture and more formally within strong-field approximation. present an analytical formula for...

The effect of vibrational motion on harmonic generation in molecules is studied within the strong-field approximation. Simple expressions are given for cut-off energy and ratio spectral intensities from two isotopes. latter based electronic trajectories simple-man's model. influence vibration by a correlation function that sensitive to overlap between initial wave packet after evolution Born–Oppenheimer potential ionized molecule.

We analyse three different formulations of the strong-field approximation for high-harmonic generation in diatomic molecules, based on length, velocity and acceleration form recombination amplitude. compare predictions two-centre interference with those from time-dependent Schrödinger equation. find that gives closest agreement exact results while being simplest a computational point view.

We develop the strong-field approximation for high-order harmonic generation in hydrogen molecules, including vibrational motion and laser-induced coupling of lowest two Born-Oppenheimer states molecular ion that is created by initial ionization molecule. show field dressing becomes important at long laser wavelengths $(\ensuremath{\approx}2\text{ }\ensuremath{\mu}\text{m})$, leading to an overall reduction modifying ratio signals from different isotopes.

We analyze the orientation dependence of harmonic amplitudes and phases from laser driven ${\text{H}}_{2}^{+}$. use Lewenstein model, with without employing saddle-point approximation for summation over electron momenta. This means that direction motion is not necessarily restricted to polarization axis in contrast previous implementations. The model predicts smooth phase jumps by almost $\ensuremath{\pi}$ dependence. demonstrates smoothness can be explained Coulomb effects, but these may...

At high intensities, three-step recollision processes driven by low frequency laser pulses, such as high-order harmonic generation and above-threshold ionization, are normally severely suppressed the magnetic-field component of field. It is shown that this suppression not severe, even for ponderomotive energies well above 10 keV, multicharged ions moving at a sufficiently relativistic velocity against counterpropagating infrared pulse. Numerical results presented emission single...

By numerical solution of the time-dependent Schr\"odinger equation, highly accurate electron spectra are calculated for strong-field ionization a one-dimensional $\mathrm{H}_{2}{}^{+}$ molecular ion at large internuclear distances. Compared to atomic spectra, we find additional cutoffs high energies. The classical model (simple-man's model) adapted geometry predicts up $50{U}_{\mathrm{p}}$, where ${U}_{\mathrm{p}}$ is ponderomotive potential. correspond various scattering scenarios tunneled...

A technique for probing ultrafast (attosecond) structural rearrangement in molecules following laser ionization is discussed. The temporal window accessible has recently been extended beyond that previously reported by employing a driving field the mid-IR.

We have developed an analytical theory explaining how the single-atom efficiency of high-harmonic generation scales with laser frequency, and verified this by numerically solving time-dependent Schrödinger equation in three spatial dimensions. According to our saddle-point analysis quantum paths, imaginary part action has a significant impact on scaling law. Furthermore, we found that law depends properties ground–continuum transition matrix element. Our elucidates relative contributions...

The generation of high-order harmonics in small diatomic molecules is theoretically investigated with inclusion the vibrational degree freedom. results obtained from solution time-dependent Schrödinger equation for a model H2 molecule are interpreted by analysing influence motion framework strong-field approximation. Ionization launches wave packet whose correlated continuum electron packet. sensitive to correlation function quantifying overlap between at time recombination and target...

Abstract A new technique for probing the structural rearrangements of molecules following ionization has recently been demonstrated. Whilst straightforward to implement, this offers remarkable time resolution, allowing intramolecular nuclear dynamics be followed with a precision 100 as. Here we discuss technique, termed PACER (probing attosecond by chirp encoded recollision), examine processes that affect measurement, and compare alternative methods vibrational wavepackets in light...

At high laser intensities, three step recollision processes such as order harmonic generation and high-order ATI, are normally severely suppressed due to the magnetic field component of pulse. However, if pulse relativistic ion beam directed against each other, a significant increase in frequency intensity rest frame ions can occur. By performing calculations based on Coulomb-corrected nondipole strong approximation, we have shown that there is range Lorentz factors, charges for which...

A technique for probing ultrafast (attosecond) structural rearrangement in molecules following laser ionization is discussed. The temporal window accessible has recently been extended beyond that previously reported by employing a driving field the mid-IR.

By applying time-dependent density functional theory to a two-dimensional multielectron atom subject strong circularly polarized light pulses, we confirm that the ionization of p orbitals with defined angular momentum depends on sense rotation applied field. A simple ad-hoc modification adiabatic local-density exchange-correlation is proposed remedy its unphysical behavior under orbital depletion.

Abstract We propose a simple, computationally efficient scheme for an X-ray spectrum simulator. The theoretical models describing the physical processes involved are employed in our Monte Carlo software coherent way, paving way straightforward future improvements. Our results compare satisfactorily to experimental from literature and dedicated simulation software. simplicity, excellent statistical errors, short execution time of code recommend it intensive use generation simulations.