35 research outputs found
High-order Harmonic Spectroscopy of the Cooper Minimum in Argon: Experimental and Theoretical Study
We study the Cooper minimum in high harmonic generation from argon atoms
using long wavelength laser pulses. We find that the minimum in high harmonic
spectra is systematically shifted with respect to total photoionization cross
section measurements. We use a semi-classical theoretical approach based on
Classical Trajectory Monte Carlo and Quantum Electron Scattering methods
(CTMC-QUEST) to model the experiment. Our study reveals that the shift between
photoionization and high harmonic emission is due to several effects: the
directivity of the recombining electrons and emitted polarization, and the
shape of the recolliding electron wavepacket.Comment: 13 page
Time-resolved predissociation of the vibrationless level of the B state of CH3I
The predissociation dynamics of the vibrationless level of the first Rydberg
state 6s (B 2E) state of CH3I has been studied by femtosecond-resolved velocity
map imaging of both the CH3 and I photofragments. The kinetic energy
distributions of the two fragments have been recorded as a function of the
pump-probe delay, and as a function of excitation within the umbrella and
stretching vibrational modes of the CH3 fragment. These observations are made
by using (2+1) Resonant Enhanced MultiPhoton Ionization (REMPI) via the 3pz
2A2" state of CH3 to detect specific vibrational levels of CH3. The vibrational
branching fractions of the CH3 are recovered by using the individual
vibrationally state-selected CH3 distributions to fit the kinetic energy
distribution obtained by using nonresonant multiphoton ionization of either the
I or CH3 fragment. The angular distributions and rise times of the two
fragments differ significantly. These observations can be rationalized through
a consideration of the alignment of the CH3 fragment and the effect of this
alignment on its detection efficiency. Two extra dissociation channels are
detected: one associated with Rydberg states near 9.2 eV that were observed
previously in photoelectron studies, and one associated with photodissociation
of the parent cation around 15 eV.Comment: submitted Physical Chemistry Chemical Physics (2011
ZnO Nanowire-based dye-sensitized solar cells: investigation of growth conditions
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Efficient generation of sub-100âeV high-order harmonics from carbon molecules using infrared laser pulses
© 2016 AIP Publishing LLC. We demonstrate broad bandwidth and intense sub-100 eV high-order harmonics from diatomic carbon molecules driven by long-wavelength laser pulses. Up to now, one limitation of the intense carbon harmonic source driven by a 0.8 ÎŒm wavelength Ti:sapphire laser has been the low cutoff around âŒ32 eV. In this paper, we show that this harmonic cutoff is extended to âŒ70 eV by increasing the driving laser wavelength to 1.71 ÎŒm. Surprisingly, the carbon harmonic intensity is found to be high despite the long wavelength driving laser. Experiments show only âŒ30% decrease in the harmonic intensity when changing the driving laser wavelength from 0.8 ÎŒm to 1.71 ÎŒm. Such intense sub-100 eV coherent X-rays would have important applications in various domains of science and technology
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High-order harmonic generation from the dressed autoionizing states.
In high-order harmonic generation, resonant harmonics (RH) are sources of intense, coherent extreme-ultraviolet radiation. However, intensity enhancement of RH only occurs for a single harmonic order, making it challenging to generate short attosecond pulses. Moreover, the mechanism involved behind such RH was circumstantial, because of the lack of direct experimental proofs. Here, we demonstrate the exact quantum paths that electron follows for RH generation using tin, showing that it involves not only the autoionizing state, but also a harmonic generation from dressed-AIS that appears as two coherent satellite harmonics at frequencies ±2Ω from the RH (Ω represents laser frequency). Our observations of harmonic emission from dressed states open the possibilities of generating intense and broadband attosecond pulses, thus contributing to future applications in attosecond science, as well as the perspective of studying the femtosecond and attosecond dynamics of autoionizing states