9 research outputs found
Explosions of water clusters in intense laser fields
Energetic, highly-charged oxygen ions, (), are copiously
produced upon laser field-induced disassembly of highly-charged water clusters,
and , 60, that are formed by seeding high-pressure
helium or argon with water vapor. clusters (n40000) formed under
similar experimental conditions are found undergo disassembly in the Coulomb
explosion regime, with the energies of ions showing a
dependence. Water clusters, which are argued to be considerably smaller in
size, should also disassemble in the same regime, but the energies of fragment
O ions are found to depend linearly on which, according to
prevailing wisdom, ought to be a signature of hydrodynamic expansion that is
expected of much larger clusters. The implication of these observations on our
understanding of the two cluster explosion regimes, Coulomb explosion and
hydrodynamic expansion, is discussed. Our results indicate that charge state
dependences of ion energy do not constitute an unambiguous experimental
signature of cluster explosion regime.Comment: Submitted to Phys. Rev.
Angle-resolved coherent wave mixing using a 4 fs ultra-broad bandwidth laser
We demonstrate angle-resolved coherent (ARC) wave mixing
using 4 fs light pulses derived from a laser source that spans
550–1000 nm. We believe this to be the shortest pulse duration
used to date in coherent multi-dimensional spectroscopy. The
marriage of this ultra-broad band, few-cycle coherent source
with the ARC technique will permit new investigations of the
interplay between energy transfers and quantum superposition
states spanning 8200 cm−1. We applied this configuration to
measurements on the photosynthetic low light (LL) complex
from Rhodopseudomonas palustris in solution at ambient
temperature. We observe bi-exponential population dynamics
for energy transfer across 5500 cm−1 (0.65 eV), which we
attribute to energy transfer from the Qx transition of bacteriochlorophylls
to the B850 pigment of the complex. We
believe for the first time, to the best of our knowledge, we
demonstrate that ARC maps can be recorded using a single
laser pulse
Ion energy measurements from the interaction of atomic and molecular clusters with intense femtosecond laser pulses
Comparative studies of resonance enhancement of harmonic radiation in indium plasma using multicycle and few-cycle pulses
Enhanced single harmonic generation is analyzed in indium laser ablation plasmas at excitation conditions of multicycle (30 fs) and few-cycle (3.5 fs) pulses. We demonstrate the strong influence of pulse duration, on the emission spectra from the indium plasma. For few-cycle pulses, the enhanced emissions do not coincide with the expected harmonic wavelengths, which is the case for multicycle pulses. We test the coherent properties of an enhanced emission around 20 eV using polarization and double-slit interference techniques. We also characterize the dynamics of the emissions from the indium plasma by tuning the laser pulse duration. A theoretical analysis is presented to describe the indium plasma emission upon excitation by few-cycle pulses. © 2013 American Physical Society.Peer Reviewe
Comparison of high-order harmonic generation in uracil and thymine ablation plumes
We present studies of high-order harmonic generation (HHG) in laser ablation plumes of the ribonucleic acid nucleobase uracil and its deoxyribonucleic acid counterpart thymine. Harmonics were generated using 780 nm, 30 fs and 1300 nm, 40 fs radiation upon ablation with 1064 nm, 10 ns or 780 nm, 160 ps pulses. Strong HHG signals were observed from uracil plumes with harmonics emitted with photon energies >55 eV. Results obtained in uracil plumes were compared with those from thymine, which did not yield signs of harmonic generation. The ablation plumes of the two compounds were examined by collection of the ablation debris on a silicon substrate placed in close proximity to the target and by time-of-flight mass spectrometry. From this evidence we conclude that the differences in HHG signal are due to the different fragmentation dynamics of the molecules in the plasma plume. These studies constitute the first attempt to analyse differences in structural properties of complex molecules through plasma ablation-induced HHG spectroscopy. © 2013 the Owner Societies.Peer Reviewe
High-order harmonic generation in graphite plasma plumes using ultrashort laser pulses: A systematic analysis of harmonic radiation and plasma conditions
High-order harmonic generation in graphite-ablated plasmas was systematically studied using ultrashort (3.5 and 30 fs) laser pulses. We observed the efficient frequency conversion of 3.5 fs Ti:sapphire laser pulses in the range of 15-26eV. Stabilization of the harmonic yield at a 1kHz pulse repetition rate was accomplished using a rotating graphite target. We also show the results of harmonic generation in carbon plasma using 1300nm, 40ps pulses, which allowed the extension of the harmonic cutoff while maintaining a comparable conversion efficiency to the case of 780nm driving radiation. The time-of-flight mass spectrometric analysis of the plasma components and the scanning electron microscopy of plasma debris under optimal conditions for harmonic generation suggest the presence of small carbon clusters (C 10-C 30) in the plasma plume at the moment of femtosecond pulse propagation, which further aggregate on nearby substrates. We present the results of plasma spectroscopy obtained under unoptimized plasma conditions that elucidate the reduction in harmonic signal. We also present calculations of plasma concentration under different excitation conditions of the ablated graphite target.Peer Reviewe