405 research outputs found
The cosmic microwave background: observing directly the early universe
The Cosmic Microwave Background (CMB) is a relict of the early universe. Its
perfect 2.725K blackbody spectrum demonstrates that the universe underwent a
hot, ionized early phase; its anisotropy (about 80 \mu K rms) provides strong
evidence for the presence of photon-matter oscillations in the primeval plasma,
shaping the initial phase of the formation of structures; its polarization
state (about 3 \mu K rms), and in particular its rotational component (less
than 0.1 \mu K rms) might allow to study the inflation process in the very
early universe, and the physics of extremely high energies, impossible to reach
with accelerators. The CMB is observed by means of microwave and mm-wave
telescopes, and its measurements drove the development of ultra-sensitive
bolometric detectors, sophisticated modulators, and advanced cryogenic and
space technologies. Here we focus on the new frontiers of CMB research: the
precision measurements of its linear polarization state, at large and
intermediate angular scales, and the measurement of the inverse-Compton effect
of CMB photons crossing clusters of Galaxies. In this framework, we will
describe the formidable experimental challenges faced by ground-based,
near-space and space experiments, using large arrays of detectors. We will show
that sensitivity and mapping speed improvement obtained with these arrays must
be accompanied by a corresponding reduction of systematic effects (especially
for CMB polarimeters), and by improved knowledge of foreground emission, to
fully exploit the huge scientific potential of these missions.Comment: In press. Plenary talk. Copyright 2012 Society of Photo-Optical
Instrumentation Engineers. One print or electronic copy may be made for
personal use only. Systematic reproduction and distribution, duplication of
any material in this paper for a fee or for commercial purposes, or
modification of the content of the paper are prohibite
Common-mode rejection in Martin-Puplett spectrometers for astronomical observations at mm-wavelengths
The Martin-Puplett interferometer (MPI) is a differential Fourier transform
spectrometer (FTS), measuring the difference between spectral brightness at two
input ports. This unique feature makes the MPI an optimal zero instrument, able
to detect small brightness gradients embeddend in a large common background. In
this paper we investigate experimentally the common-mode rejection achievable
in the MPI at mm wavelengths, and discuss the use of the instrument to measure
the spectrum of cosmic microwave background (CMB) anisotropy
Sensitivity to Cosmic Rays of Cold Electron Bolometers for Space Applications
An important phenomenon limiting the sensitivity of bolometric detectors for
future space missions is the interaction with cosmic rays. We tested the
sensitivity of Cold Electron Bolometers (CEBs) to ionizing radiation using
gamma-rays from a radioactive source and X-rays from a X-ray tube. We describe
the test setup and the results. As expected, due to the effective thermal
insulation of the sensing element and its negligible volume, we find that CEBs
are largely immune to this problem.Comment: LTD15; 6 pages, 6 figure
Optimal strategy for polarization modulation in the LSPE-SWIPE experiment
CMB B-mode experiments are required to control systematic effects with an
unprecedented level of accuracy. Polarization modulation by a half wave plate
(HWP) is a powerful technique able to mitigate a large number of the
instrumental systematics. Our goal is to optimize the polarization modulation
strategy of the upcoming LSPE-SWIPE balloon-borne experiment, devoted to the
accurate measurement of CMB polarization at large angular scales. We depart
from the nominal LSPE-SWIPE modulation strategy (HWP stepped every 60 s with a
telescope scanning at around 12 deg/s) and perform a thorough investigation of
a wide range of possible HWP schemes (either in stepped or continuously
spinning mode and at different azimuth telescope scan-speeds) in the frequency,
map and angular power spectrum domain. In addition, we probe the effect of
high-pass and band-pass filters of the data stream and explore the HWP response
in the minimal case of one detector for one operation day (critical for the
single-detector calibration process). We finally test the modulation
performance against typical HWP-induced systematics. Our analysis shows that
some stepped HWP schemes, either slowly rotating or combined with slow
telescope modulations, represent poor choices. Moreover, our results point out
that the nominal configuration may not be the most convenient choice. While a
large class of spinning designs provides comparable results in terms of pixel
angle coverage, map-making residuals and BB power spectrum standard deviations
with respect to the nominal strategy, we find that some specific configurations
(e.g., a rapidly spinning HWP with a slow gondola modulation) allow a more
efficient polarization recovery in more general real-case situations. Although
our simulations are specific to the LSPE-SWIPE mission, the general outcomes of
our analysis can be easily generalized to other CMB polarization experiments.Comment: 11 pages, 9 figures, accepted for publication in A&
Optimization of the half wave plate configuration for the LSPE-SWIPE experiment
The search for the B-mode polarization of Cosmic Microwave Background (CMB)
is the new frontier of observational Cosmology. A B-mode detection would give
an ultimate confirmation to the existence of a primordial Gravitational Wave
(GW) background as predicted in the inflationary scenario. Several experiments
have been designed or planned to observe B-modes. In this work we focus on the
forthcoming Large Scale Polarization Explorer (LSPE) experiment, that will be
devoted to the accurate measurement of CMB polarization at large angular
scales. LSPE consists of a balloon-borne bolometric instrument, the Short
Wavelength Instrument for the Polarization Explorer (SWIPE), and a ground-based
coherent polarimeter array, the STRatospheric Italian Polarimeter (STRIP).
SWIPE will employ a rotating Half Wave Plate (HWP) polarization modulator to
mitigate the systematic effects due to instrumental non-idealities. We present
here preliminary forecasts aimed at optimizing the HWP configuration.Comment: 6 pages, 4 figures, proceedings of the 7th Young Researcher Meeting,
Torino, Oct 24th-26th 201
Cold-electron bolometers for future mm and sub-mm sky surveys
Future sky surveys in the mm/sub-mm range, like the forthcoming balloon-borne
missions LSPE, OLIMPO, SPIDER etc., will need detectors insensitive to cosmic
rays (CRs) and with a NEP of the order of W/sqrt(Hz).
The Cold-Electron Bolometers (CEBs) technology is promising, having the
required properties, since the absorber volume is extremely small and the
electron system of the absorber is thermally insulated from the phonon system.
We have developed an experimental setup to test the optical performance and the
CRs insensitivity of CEBs, with the target of integrating them in the OLIMPO
and LSPE focal planes.Comment: 6 figure
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