152 research outputs found
Laser induced strong-field ionization gas jet tomography
We introduce a novel in-situ strong field ionization tomography approach for
characterizing the spatial density distribution of gas jets. We show that for
typical intensities in high harmonic generation experiments, the strong field
ionization mechanism used in our approach provides an improvement in the
resolution close to factor of 2 (resolving about 8 times smaller voxel volume),
when compared to linear/single-photon imaging modalities.
We find, that while the depth of scan in linear tomography is limited by
resolution loss due to the divergence of the driving laser beam, in the
proposed approach the depth of focus is localized due to the inherent physical
nature of strong-field interaction and discuss implications of these findings.
We explore key aspects of the proposed method and compare it with commonly used
single- and multi-photon imaging mechanisms. The proposed method will be
particularly useful for strong field and attosecond science experiments.Comment: 8 pages, 3 figure
Studying the universality of field induced tunnel ionization times via high-order harmonic spectroscopy
High-harmonics generation spectroscopy is a promising tool for resolving
electron dynamics and structure in atomic and molecular systems. This scheme,
commonly described by the strong field approximation, requires a deep insight
into the basic mechanism that leads to the harmonics generation. Recently, we
have demonstrated the ability to resolve the first stage of the process --
field induced tunnel ionization -- by adding a weak perturbation to the strong
fundamental field. Here we generalize this approach and show that the
assumptions behind the strong field approximation are valid over a wide range
of tunnel ionization conditions. Performing a systematic study -- modifying the
fundamental wavelength, intensity and atomic system -- we observed a good
agreement with quantum path analysis over a range of Keldysh parameters. The
generality of this scheme opens new perspectives in high harmonics
spectroscopy, holding the potential of probing large, complex molecular
systems.Comment: 11 pages, 5 figure
Spectrometer for X-ray emission experiments at FERMI free-electron-laser
A portable and compact photon spectrometer to be used for photon in-photon out experiments, in particular x-ray emission spectroscopy, is presented. The instrument operates in the 25\u2013800 eV energy range to cover the full emissions of the FEL1 and FEL2 stages of FERMI. The optical design consists of two interchangeable spherical varied-lined-spaced gratings and a CCD detector. Different input sections can be accommodated, with/without an entrance slit and with/without an additional relay mirror, that allow to mount the spectrometer in different end-stations and at variable distances from the target area both at synchrotron and at free-electron-laser beamlines. The characterization on the Gas Phase beamline at ELETTRA Synchrotron (Italy) is presented
Ultrafast THz probe of photo-induced polarons in lead-halide perovskites
We study the nature of photo-excited charge carriers in CsPbBr3 nanocrystal
thin films by ultrafast optical pump - THz probe spectroscopy. We observe a
deviation from a pure Drude dispersion of the THz dielectric response that is
ascribed to the polaronic nature of carriers; a transient blueshift of observed
phonon frequencies is indicative of the coupling between photogenerated charges
and stretching-bending modes of the deformed inorganic sublattice, as confirmed
by DFT calculations
Generation of ultrashort pulses by four wave mixing in a gas-filled hollow core fiber
The four wave mixing (FWM) process is widely exploited for the generation of tunable ultrashort light pulses. Usually this process is driven in bulk materials, which are however prone to optical damage at high pump laser intensities. A tunable source of ultrashort 10 mu J level pulses in the visible spectral region is described here. In particular, we report on the implementation of FWM driven by a two-color ultrafast laser pulse inside a gas-filled hollow core fiber (HCF). Due to the high-damage threshold and the long interaction distance, the HCF-based FWM configuration proves to be suitable for high-energy applications. Moreover, this technique can be potentially used for ultrashort pulses generation within a wide range of spectral regions; a discussion on the possibility to extend our scheme to the generation of few-cycle mid-IR pulse is provided
Fast stabilization of a high-energy ultrafast OPA with adaptive lenses
The use of fast closed-loop adaptive optics has improved the performance of optical systems since its first application. Here we demonstrate the amplitude and carrier-envelope phase stabilization of a high energy IR optical parametric amplifier devoted to Attosecond Science exploiting two high speed adaptive optical systems for the correction of static and dynamic instabilities. The exploitation of multi actuator adaptive lenses allowed for a minimal impact on the optical setup
Multidimensional high harmonic spectroscopy of polyatomic molecules: detecting sub-cycle laser-driven hole dynamics upon ionization in strong mid-IR laser fields
High harmonic generation (HHG) spectroscopy has opened up a new frontier in ultrafast science, where electronic dynamics can be measured on an attosecond time scale. The strong laser field that triggers the high harmonic response also opens multiple quantum pathways for multielectron dynamics in molecules, resulting in a complex process of multielectron rearrangement during ionization. Using combined experimental and theoretical approaches, we show how multi-dimensional HHG spectroscopy can be used to detect and follow electronic dynamics of core rearrangement on sub-laser cycle time scales. We detect the signatures of laser-driven hole dynamics upon ionization and reconstruct the relative phases and amplitudes for relevant ionization channels in a CO2 molecule on a sub-cycle time scale. Reconstruction of channel-resolved complex ionization amplitudes on attosecond time scales has been a long-standing goal of high harmonic spectroscopy. Our study brings us one step closer to fulfilling this initial promise and developing robust schemes for sub-femtosecond imaging of multielectron rearrangement in complex molecular systems
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