439 research outputs found
Frequency comb vernier spectroscopy in the near infrared
We perform femtosecond frequency comb vernier spectroscopy in the near
infrared with a femtosecond Er doped fiber laser, a scanning high-finesse
cavity and an InGaAs camera. By utilizing the properties of a frequency comb
and a scanning high-finesse cavity such spectroscopy provides broad spectral
bandwidth, high spectral resolution, and high detection sensitivity on a short
time scale. We achieved an absorption sensitivity of ~8E-8 cm-1Hz-1/2
corresponding to a detection limit of ~70 ppbv for acetylene, with a resolution
of ~1.1 GHz in single images taken in 0.5 seconds and covering a frequency
range of ~5 THz. These measurements have broad applications for sensing other
greenhouse gases in this fingerprint near IR region with a simple apparatus.Comment: 14 pages, 5 figure
Reconstruction of ionization probabilities from spatially averaged data in N-dimensions
We present an analytical inversion technique which can be used to recover
ionization probabilities from spatially averaged data in an N-dimensional
detection scheme. The solution is given as a power series in intensity. For
this reason, we call this technique a multiphoton expansion (MPE). The MPE
formalism was verified with an exactly solvable inversion problem in 2D, and
probabilities in the postsaturation region, where the intensity-selective
scanning approach breaks down, were recovered. In 3D, ionization probabilities
of Xe were successfully recovered with MPE from simulated (using the ADK
tunneling theory) ion yields. Finally, we tested our approach with
intensity-resolved benzene ion yields showing a resonant multiphoton ionization
process. By applying MPE to this data (which was artificially averaged) the
resonant structure was recovered-suggesting that the resonance in benzene may
have been observable in spatially averaged data taken elsewhere.Comment: 19 pages and 3 figure
Surface plasmon resonance study of the actin-myosin sarcomeric complex and tubulin dimers
Biosensors based on the principle of surface plasmon resonance (SPR)
detection were used to measure biomolecular interactions in sarcomeres and
changes of the dielectric constant of tubulin samples with varying
concentration. At SPR, photons of laser light efficiently excite surface
plasmons propagating along a metal (gold) film. This resonance manifests itself
as a sharp minimum in the reflection of the incident laser light and occurs at
a characteristic angle. The dependence of the SPR angle on the dielectric
permittivity of the sample medium adjacent to the gold film allows the
monitoring of molecular interactions at the surface. We present results of
measurements of cross-bridge attachment/detachment within intact mouse heart
muscle sarcomeres and measurements on bovine tubulin molecules pertinent to
cytoskeletal signal transduction models.Comment: Submitted to Journal of Modern Optics *Corresponding author: Andreas
Mershin ([email protected]
Intrinsic and extrinsic x-ray absorption effects in soft x-ray diffraction from the superstructure in magnetite
We studied the (001/2) diffraction peak in the low-temperature phase of
magnetite (Fe3O4) using resonant soft x-ray diffraction (RSXD) at the Fe-L2,3
and O-K resonance. We studied both molecular-beam-epitaxy (MBE) grown thin
films and in-situ cleaved single crystals. From the comparison we have been
able to determine quantitatively the contribution of intrinsic absorption
effects, thereby arriving at a consistent result for the (001/2) diffraction
peak spectrum. Our data also allow for the identification of extrinsic effects,
e.g. for a detailed modeling of the spectra in case a "dead" surface layer is
present that is only absorbing photons but does not contribute to the
scattering signal.Comment: to appear in Phys. Rev.
Observation of anisotropic fragmentation in methane subjected to femtosecond radiation
We present experimental results on the ionization/dissociation of methane in
femtosecond pulses of radiation. Angular and intensity dependent yields of
singly and doubly charged species were measured using an imaging mass
spectrometer. The measured data shows that all fragments yields exhibit some
degree of anisotropy as a result of them being preferably ejected parallel to
the polarization direction. Additionally, an anomalous perpendicular
fragmentation pattern is found for CH\-(2)\+(2+). We find evidence of multiple
dissociation mechanisms including statistical decay, field assisted
dissociation and Coulomb explosion.Comment: 24 pages, 7 figure
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