Revealing quantum path details in high-field physics

Abstract

The fundamental mechanism underlying harmonic emission in the strong-field regime is governed by tunnel ionization of the atom, followed by the motion of the electron wave packet in the continuum, and finally by its recollision with the atomic core. Due to the quantum nature of the process, the properties of the electron wave packet strongly correlate with those of the emitted radiation. Here, by spatially resolving the interference pattern generated by overlapping the harmonic radiation emitted by different interfering electron quantum paths, we have succeeded in unravelling the intricacies associated with the recollision process. This has been achieved by mapping the spatial extreme-ultraviolet (EUV)-intensity distribution onto a spatial ion distribution, produced in the EUV focal area through the linear and nonlinear processes of atoms. By in situ manipulation of the intensity-dependent motion of the electron wave packets, we have been able to directly measure the difference between the harmonic emission times and electron path lengths resulting from different electron trajectories. Due to the high degree of accuracy that the present approach provides, we have been able to demonstrate the quantum nature of the recollision process. This is done by quantitatively correlating the photoemission time and the electron quantum path-length differences, taking into account the energy-momentum transfer from the driving laser field into the system. This information paves the way for electron-photon correlation studies at the attosecond time scale, while it puts the recollision process from the semiclassical prospective into a full quantum-mechanical context.

Tabletop nonlinear optics in the 100-eV spectral region

“…In order to explore the interaction of the XUV pulse with the target gas, we use an ion microscope (IM) [37][38][39] to record the spatial distribution of the different photo ions in the XUV focus. More specifically, the IM records the y-projection of the ion distribution as a function of their time of flight (TOF) with single-ion sensitivity.…”

Generation of Attosecond Light Pulses from Gas and Solid State Media

“…In this context the harmonic spectrum is obtained by the Fourier transform of the time-dependent dipole moment which contains an integral over all possible electron trajectories characterized by ionization time (t i ), recombination time (t r ), and momentum p. Using a saddle-point analysis it can be shown that, for a given driving laser intensity I L , there are two interfering quantum [95][96][97][98][99] electron trajectories (the "Long" and the "Short" noted as L and S in the down panel of Figure 1b…”

“…Normal incidence spherical mirrors with reflectivity 10%-20% have been used for focusing an XUV beam of~20 eV photon energy in the sub-4 µm level reaching intensities >10 13 W/cm 2 [150] while multilayer mirrors have been used for focusing an XUV beam of~90 eV photon energy [29]. This XUV focusing geometry has been extensively used for the temporal characterization of asec pulses via IR/XUV cross-correlation [29,97,146], 2nd-order autocorrelation approaches (using spit spherical mirror in unit 5 or spit silicon plates in unit 3) [45,47,48,50,54,97], and for imaging the ion distribution produced by linear and non-linear processes at the focus of the XUV beam [98,150]. In order to characterize the XUV beam after the interaction with the system under investigation, XUV diagnostics as those described in unit 4 can also be placed at the output of the 5th unit.…”

“…The measured photoelectron distribution does not differ significantly from the XUV spectral distribution as in the photon energy range between 15 eV and 30 eV the single-photon-ionization cross section of Argon is almost constant. Ions are measured using an Ion Microscope (IM) [98,155] (down branch in unit 5 of Figure 8a) that images the focal area onto a Micro-channel Plate (MCP) detector equipped with a phosphor (Ph) screen anode. The resolution of the IM is ≈ 1 µm.…”

Disclosing intrinsic molecular dynamics on the 1-fs scale through extreme-ultraviolet pump-probe measurements

“…The filter quality, in terms of IR transmission, was checked by means of an IR-XUV-beam profiler placed behind the filter foil, and the energy of the XUV radiation was measured using a calibrated XUV photodiode. The focus of the XUV beam in the detection area was characterized by means of an ion microscope detector [27]. The emitted XUV spectrum was recorded by measuring the energy-resolved photoelectron spectrum of the single-photon ionization of Xe.…”