17 research outputs found
Femtosecond photoelectron and photoion spectrometer with vacuum ultraviolet probe pulses
We describe a setup to study ultrafast dynamics in gas-phase molecules using
time-resolved photoelectron and photoion spectroscopy. The vacuum ultraviolet
(VUV) probe pulses are generated via strong field high-order harmonic
generation from infrared femtosecond laser pulses. The band pass characteristic
in transmission of thin indium (In) metal foil is exploited to isolate the
harmonic of the 800 nm fundamental (H9, 14 eV, 89 nm) from all
other high harmonics. The harmonic is obtained with high
conversion efficiencies and has sufficient photon energy to access the complete
set of valence electron levels in most molecules. The setup also allows for
direct comparison of VUV single-photon probe with 800 nm multi-photon probe
without influencing the delay of excitation and probe pulse or the beam
geometry. We use a magnetic bottle spectrometer with high collection efficiency
for electrons, serving at the same time as a time of flight spectrometer for
ions. Characterization measurements on Xe reveal the spectral width of H9 to be
meV and a photon flux of photons/pulse after
spectral filtering. As a first application, we investigate the S excitation
of perylene using time-resolved ion spectra obtained with multi-photon probing
and time-resolved electron spectra from VUV single-photon probing. The time
resolution extracted from cross-correlation measurements is fs for
both probing schemes and the pulse duration of H9 is found to be fs
Wavelength Scaling of Laser Wakefield Acceleration for the EuPRAXIA Design Point
Scaling the particle beam luminosity from laser wakefield accelerators to meet the needs of the physics community requires a significant, thousand-fold increase in the average power of the driving lasers. Multipulse extraction is a promising technique capable of scaling high peak power lasers by that thousand-fold increase in average power. However, several of the best candidate materials for use in multipulse extraction amplifiers lase at wavelengths far from the 0.8–1.0 μm region which currently dominates laser wakefield research. In particular, we have identified Tm:YLF, which lases near 1.9 µm, as the most promising candidate for high average power multipulse extraction amplifiers. Current schemes to scale the laser, plasma, and electron beam parameters to alternative wavelengths are unnecessarily restrictive in that they stress laser performance gains to keep plasma conditions constant. In this paper, we present a new and more general scheme for wavelength scaling a laser wakefield acceleration (LWFA) design point that provides greater flexibility in trading laser, plasma, and electron beam parameters within a particular design point. Finally, a multipulse extraction 1.9 µm Tm:YLF laser design meeting the EuPRAXIA project’s laser goals is discussed
Laser-induced electron diffraction for probing rare gas atoms
Recently, using midinfrared laser-induced electron diffraction (LIED), snapshots of a vibrating diatomic molecule on a femtosecond time scale have been captured [C. I. Blaga et al., Nature (London) 483, 194 (2012)]. In this Letter, a comprehensive treatment for the atomic LIED response is reported, a critical step in generalizing this imaging method. Electron-ion differential cross sections (DCSs) of rare gas atoms are extracted from measured angular-resolved, high-energy electron momentum distributions generated by intense midinfrared lasers. Following strong-field ionization, the high-energy electrons result from elastic rescattering of a field-driven wave packet with the parent ion. For recollision energies 100 eV, the measured DCSs are indistinguishable for the neutral atoms and ions, illustrating the close collision nature of
this interaction. The extracted DCSs are found to be independent of laser parameters, in agreement with theory. This study establishes the key ingredients for applying LIED to femtosecond molecular imaging
Extreme Ultraviolet Transient Grating Measurement of Insulator-Metal Transition Dynamics in VO2
We demonstrate spectrally resolved transient grating (TG) spectroscopy in the extreme ultraviolet (EUV) near the M-edge of vanadium dioxide. Time-dependent and broadband EUV-TG measurements separate the index of refraction change due to the insulator to metal transition from purely acoustic effects
Self Referencing Heterodyne Transient Grating Spectroscopy with Short Wavelength
Heterodyning by a phase stable reference electric field is a well known technique to amplify weak nonlinear signals. For short wavelength, the generation of a reference field in front of the sample is challenging because of a lack of suitable beamsplitters. Here, we use a permanent grating which matches the line spacing of the transient grating for the creation of a phase stable reference field. The relative phase among the two can be changed by a relative translation of the permanent and transient gratings in direction orthogonal to the grating lines. We demonstrate the technique for a transient grating on a VO2 thin film and observe constructive as well as destructive interference signals
Broadband extreme ultraviolet probing of transient gratings in vanadium dioxide
Nonlinear spectroscopy in the extreme ultraviolet (EUV) and soft x-ray spectral range offers the opportunity for element selective probing of ultrafast dynamics using core-valence transitions (Mukamel et al., Acc. Chem. Res. 42, 553 (2009)). We demonstrate a step on this path showing core-valence sensitivity in transient grating spectroscopy with EUV probing. We study the optically induced insulator-to-metal transition (IMT) of a VO2 film with EUV diffraction from the optically excited sample. The VO2 exhibits a change in the 3p-3d resonance of V accompanied by an acoustic response. Due to the broadband probing we are able to separate the two features. (C) 2015 Optical Society of Americ