256 research outputs found
Generation of the second-harmonic Bessel beams via nonlinear Bragg diffraction
We generate conical second-harmonic radiation by transverse excitation of a
two-dimensional annular periodically-poled nonlinear photonic structure with a
fundamental Gaussian beam. We show that these conical waves are the far-field
images of the Bessel beams generated in a crystal by parametric frequency
conversion assisted by nonlinear Bragg diffraction.Comment: 4 pages, 5 figures. submitte
Fractoluminescence characterization of the energy dissipated during fast fracture of glass
Fractoluminescence experiments are performed on two kinds of silicate
glasses. All the light spectra collected during dynamic fracture reveal a black
body radiator behaviour, which is interpreted as a crack velocity-dependent
temperature rise close to the crack tip. Crack velocities are estimated to be
of the order of 1300 m.s and fracture process zones are shown to extend
over a few nanometers.Comment: Accepted for publication in Europhysics Letters; 5 pages; 4 figure
Status of the LHCb magnet system
The LHCb experiment focuses on the precision measurement of CP violation and rare decays in the B-meson system. It plans to operate with an average luminosity of ~cms, which should be obtained from the beginning of the LHC operation. The LHCb detector exploits the forward region of the pp collisions at the LHC collider. It requires a single-arm spectrometer for the separation and momentum measurement of the charged particles with a large dipole magnet of a free aperture of ~mrad horizontally and ~mrad vertically. The magnet is designed for a total integrated field of 4~Tm. The pole gap is 2.2 to 3.5~m vertically (the direction of the field) and 2.6 to 4.2~m horizontally. The overall length of the magnet (in beam direction) is 5~m and its total weight about 1500~t. The power dissipation in the aluminium coils will be 4.2~MW. The magnet yoke is constructed from low carbon steel plates of 100~mm thickness. The maximum weight of one plate does not exceed 25~t. The coils are wound from large hollow aluminium conductor of cross-section with a central cooling channel of 25~mm diameter for the pressurized demineralized water. Each of the two coils is composed of 15~monolayer pancakes of 15~turns per pancake. To reach good field quality the coils are bent by 45 towards the gap along the horizontal aperture of ~mrad and the pole pieces have large shims. The underlying magnet design, its present status and milestones will be reviewed
PILOT: a balloon-borne experiment to measure the polarized FIR emission of dust grains in the interstellar medium
Future cosmology space missions will concentrate on measuring the
polarization of the Cosmic Microwave Background, which potentially carries
invaluable information about the earliest phases of the evolution of our
universe. Such ambitious projects will ultimately be limited by the sensitivity
of the instrument and by the accuracy at which polarized foreground emission
from our own Galaxy can be subtracted out. We present the PILOT balloon project
which will aim at characterizing one of these foreground sources, the
polarization of the dust continuum emission in the diffuse interstellar medium.
The PILOT experiment will also constitute a test-bed for using multiplexed
bolometer arrays for polarization measurements. We present the results of
ground tests obtained just before the first flight of the instrument.Comment: 17 pages, 13 figures. Presented at SPIE, Millimeter, Submillimeter,
and Far-Infrared Detectors and Instrumentation for Astronomy VII. To be
published in Proc. SPIE volume 915
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Impact of particles on the Planck HFI detectors: Ground-based measurements and physical interpretation
The Planck High Frequency Instrument (HFI) surveyed the sky continuously from
August 2009 to January 2012. Its noise and sensitivity performance were
excellent, but the rate of cosmic ray impacts on the HFI detectors was
unexpectedly high. Furthermore, collisions of cosmic rays with the focal plane
produced transient signals in the data (glitches) with a wide range of
characteristics. A study of cosmic ray impacts on the HFI detector modules has
been undertaken to categorize and characterize the glitches, to correct the HFI
time-ordered data, and understand the residual effects on Planck maps and data
products. This paper presents an evaluation of the physical origins of glitches
observed by the HFI detectors. In order to better understand the glitches
observed by HFI in flight, several ground-based experiments were conducted with
flight-spare HFI bolometer modules. The experiments were conducted between 2010
and 2013 with HFI test bolometers in different configurations using varying
particles and impact energies. The bolometer modules were exposed to 23 MeV
protons from the Orsay IPN TANDEM accelerator, and to Am and Cm
-particle and Fe radioactive X-ray sources. The calibration data
from the HFI ground-based preflight tests were used to further characterize the
glitches and compare glitch rates with statistical expectations under
laboratory conditions. Test results provide strong evidence that the dominant
family of glitches observed in flight are due to cosmic ray absorption by the
silicon die substrate on which the HFI detectors reside. Glitch energy is
propagated to the thermistor by ballistic phonons, while there is also a
thermal diffusion contribution. The implications of these results for future
satellite missions, especially those in the far-infrared to sub-millimetre and
millimetre regions of the electromagnetic spectrum, are discussed.Comment: 11 pages, 13 figure
In-flight calibration and verification of the Planck-LFI instrument
In this paper we discuss the Planck-LFI in-flight calibration campaign. After
a brief overview of the ground test campaigns, we describe in detail the
calibration and performance verification (CPV) phase, carried out in space
during and just after the cool-down of LFI. We discuss in detail the
functionality verification, the tuning of the front-end and warm electronics,
the preliminary performance assessment and the thermal susceptibility tests.
The logic, sequence, goals and results of the in-flight tests are discussed.
All the calibration activities were successfully carried out and the instrument
response was comparable to the one observed on ground. For some channels the
in-flight tuning activity allowed us to improve significantly the noise
performance.Comment: Long technical paper on Planck LFI in flight calibration campaign:
109 pages in this (not final) version, 100 page in the final JINST versio
The Planck High Frequency Instrument, a 3rd generation CMB experiment, and a full sky submillimeter survey
The High Frequency Instrument (HFI) of Planck is the most sensitive CMB
experiment ever planned. Statistical fluctuations (photon noise) of the CMB
itself will be the major limitation to the sensitivity of the CMB channels.
Higher frequency channels will measure galactic foregrounds. Together with the
Low Frequency Instrument, this will make a unique tool to measure the full sky
and to separate the various components of its spectrum. Measurement of the
polarization of these various components will give a new picture of the CMB. In
addition, HFI will provide the scientific community with new full sky maps of
intensity and polarization at six frequencies, with unprecedented angular
resolution and sensitivity. This paper describes the logics that prevailed to
define the HFI and the performances expected from this instrument. It details
several features of the HFI design that have not been published up to now.Comment: To be published in the proceedings of the workshop on "The Cosmic
Microwave Background and its Polarization", New Astronomy Reviews, (eds., S.
Hanany and R.A. Olive
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