1,694 research outputs found
Momentum space tomographic imaging of photoelectrons
We apply tomography, a general method for reconstructing 3-D distributions
from multiple projections, to reconstruct the momentum distribution of
electrons produced via strong field photoionization. The projections are
obtained by rotating the electron distribution via the polarization of the
ionizing laser beam and recording a momentum spectrum at each angle with a 2-D
velocity map imaging spectrometer. For linearly polarized light the tomographic
reconstruction agrees with the distribution obtained using an Abel inversion.
Electron tomography, which can be applied to any polarization, will simplify
the technology of electron imaging. The method can be directly generalized to
other charged particles.Comment: Accepted by J. Phys.
Alignment dependent enhancement of the photo-electron cutoff for multi-photon ionization of molecules
The multiphoton ionization rate of molecules depends on the alignment of the
molecular axis with respect to the ionizing laser polarization. By studying
molecular frame photo-electron angular distributions from N, O and
benzene, we illustrate how the angle-dependent ionization rate affects the
photo-electron cutoff energy. We find alignment can enhance the high energy
cutoff of the photo-electron spectrum when probing along a nodal plane or when
ionization is otherwise suppressed. This is supported by calculations using a
tunneling model with a single ion state.Comment: 4 pages, 4 figure
Waiting and Residence Times of Brownian Interface Fluctuations
We report on the residence times of capillary waves above a given height
and on the typical waiting time in between such fluctuations. The measurements
were made on phase separated colloid-polymer systems by laser scanning confocal
microscopy. Due to the Brownian character of the process, the stochastics vary
with the chosen measurement interval . In experiments, the discrete
scanning times are a practical cutoff and we are able to measure the waiting
time as a function of this cutoff. The measurement interval dependence of the
observed waiting and residence times turns out to be solely determined by the
time dependent height-height correlation function . We find excellent
agreement with the theory presented here along with the experiments.Comment: 5 figure
Advanced deep space communication systems study Final report
Deep space communication system requirements for period 1970 to 198
Partitioning of the linear photon momentum in multiphoton ionization
The balance of the linear photon momentum in multiphoton ionization is
studied experimentally. In the experiment argon and neon atoms are singly
ionized by circularly polarized laser pulses with a wavelength of 800 nm and
1400 nm in the intensity range of 10^{14} - 10^{15} W/cm^2. The photoelectrons
are measured using velocity map imaging. We find that the photoelectrons carry
linear momentum corresponding to the photons absorbed above the field free
ionization threshold. Our finding has implications for concurrent models of the
generation of terahertz radiation in filaments.Comment: 4 pages, 3 figure
Degeneracy analysis for a super cell of a photonic crystal and its application to the creation of band gaps
A method is introduced to analyze the degeneracy properties of the band
structure of a photonic crystal making use of the super cells. The band
structure associated with a super cell of a photonic crystal has degeneracies
at the edge of the Brillouin zone if the photonic crystal has some kind of
point group symmetry. Both E-polarization and H-polarization cases have the
same degeneracies for a 2-dimensional (2D) photonic crystal. Two theorems are
given and proved. These degeneracies can be lifted to create photonic band gaps
by changing the transform matrix between the super cell and the smallest unit
cell. The existence of the photonic band gaps for many known 2D photonic
crystals is explained through the degeneracy analysis.Comment: 19 pages, revtex4, 14 figures, p
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