129 research outputs found
Casimir force measurements in Au-Au and Au-Si cavities at low temperature
We report on measurements of the Casimir force in a sphere-plane geometry
using a cryogenic force microscope to move the force probe in situ over
different materials. We show how the electrostatic environment of the
interacting surfaces plays an important role in weak force measurements and can
overcome the Casimir force at large distance. After minimizing these parasitic
forces, we measure the Casimir force between a gold-coated sphere and either a
gold-coated or a heavily doped silicon surface in the 100-400 nm distance
range. We compare the experimental data with theoretical predictions and
discuss the consequence of a systematic error in the scanner calibration on the
agreement between experiment and theory. The relative force over the two
surfaces compares favorably with theory at short distance, showing that this
Casimir force experiment is sensitive to the dielectric properties of the
interacting surfaces.Comment: accepted for publication in Physical Review
Evaluation of two thermal neutron detection units consisting of ZnS/LiF scintillating layers with embedded WLS fibers read out with a SiPM
Two single channel detection units for thermal neutron detection are
investigated in a neutron beam. They consist of two ZnS/LiF scintillating
layers sandwiching an array of WLS fibers. The pattern of this units can be
repeated laterally and vertically in order to build up a one dimensional
position sensitive multi-channel detector with the needed sensitive surface and
with the required neutron absorption probability. The originality of this work
arises from the fact that the WLS fibers are read out with SiPMs instead of the
traditionally used PMTs or MaPMTs. The signal processing system is based on a
photon counting approach. For SiPMs with a dark count rate as high as 0.7 MHz,
a trigger efficiency of 80% is achieved together with a system background rate
lower than Hz and a dead time of 30 s. No change of
performance is observed for neutron count rates of up to 3.6 kHz.Comment: Submitted to Nuclear Instruments and Methods
Negative Backaction Noise in Interferometric Detection of a Microlever
Interferometric detection of mirror displacements is intrinsically limited by
laser shot noise. In practice, however, it is often limited by thermal noise.
Here we report on an experiment performed at the liquid helium temperature to
overcome the thermal noise limitation and investigate the effect of classical
laser noise on a microlever that forms a Fabry-Perot cavity with an optical
fiber. The spectral noise densities show a region of negative contribution of
the backaction noise close to the resonance frequency. We interpret this noise
reduction as a coherent coupling of the microlever to the laser intensity
noise. This optomechanical effect could be used to improve the detection
sensitivity as discussed in proposals going beyond the Standard Quantum Limit.Comment: accepted for publication in Physical Review Letter
Application of third generation synchrotron source to studies of noncrystalline materials : In-Se amorphous films
The local structure of vacuum evaporated In-Se amorphous films, containing 50, 60, and 66 at .% Se, was studied using differential anomalous X -ray scattering and extended X -ray absorption fine structure. Both intensity and absorption spectra were measured in the vicinity of the absorption K -edge of Se. The differential anomalous X -ray scattering data were converted to real space by the inverse Fourier transform yielding the differential radial distribution functions. The obtained results provide evidence for the presence of
Se-In spatial correlations for In5 0 Se50 and Se-In and Se-Se correlations for In40 Se60 and In34 Se66 within the first coordination sphere
Absorption corrections and digital filtering of X-ray diffraction profiles recorded with a position-sensitive detector
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