5,302,042 research outputs found
Sensitivity of double resonance alignment magnetometers
We present an experimental study of the intrinsic magnetometric sensitivity
of an optical/rf-frequency double resonance magnetometer in which linearly
polarized laser light is used in the optical pumping and detection processes.
We show that a semi-empirical model of the magnetometer can be used to describe
the magnetic resonance spectra. Then, we present an efficient method to predict
the optimum operating point of the magnetometer, i.e., the light power and rf
Rabi frequency providing maximum magnetometric sensitivity. Finally, we apply
the method to investigate the evolution of the optimum operating point with
temperature. The method is very efficient to determine relaxation rates and
thus allowed us to determine the three collisional disalignment cross sections
for the components of the alignment tensor. Both first and second harmonic
signals from the magnetometer are considered and compared
Coordinated mm/sub-mm observations of Sagittarius A* in May 2007
At the center of the Milky Way, with a distance of ~8 kpc, the compact source
Sagittarius A* (SgrA*) can be associated with a super massive black hole of
~4x10^6 solar masses. SgrA* shows strong variability from the radio to the
X-ray wavelength domains. Here we report on simultaneous
NIR/sub-millimeter/X-ray observations from May 2007 that involved the NACO
adaptive optics (AO) instrument at the European Southern Observatory's Very
Large Telescope, the Australian Telescope Compact Array (ATCA), the US mm-array
CARMA, the IRAM 30m mm-telescope, and other telescopes. We concentrate on the
time series of mm/sub-mm data from CARMA, ATCA, and the MAMBO bolometer at the
IRAM 30m telescope.Comment: 7 pages, 3 figures, contribution for the conference "The Universe
under the Microscope" (AHAR 2008), to be published in Journal of Physics:
Conference Series by Institute of Physics Publishin
A cryogenic waveplate rotator for polarimetry at mm and sub-mm wavelengths
Mm and sub-mm waves polarimetry is the new frontier of research in Cosmic
Microwave Background and Interstellar Dust studies. Polarimeters working in the
IR to MM range need to be operated at cryogenic temperatures, to limit the
systematic effects related to the emission of the polarization analyzer. In
this paper we study the effect of the temperature of the different components
of a waveplate polarimeter, and describe a system able to rotate, in a
completely automated way, a birefringent crystal at 4K. We simulate the main
systematic effects related to the temperature and non-ideality of the optical
components in a Stokes polarimeter. To limit these effects, a cryogenic
implementation of the polarimeter is mandatory. In our system, the rotation
produced by a step motor, running at room temperature, is transmitted down to
cryogenic temperatures by means of a long shaft and gears running on custom
cryogenic bearings. Our system is able to rotate, in a completely automated
way, a birefringent crystal at 4K, dissipating only a few mW in the cold
environment. A readout system based on optical fibers allows to control the
rotation of the crystal to better than 0.1{\deg}. This device fulfills the
stringent requirements for operation in cryogenic space experiments, like the
forthcoming PILOT, BOOMERanG and LSPE.Comment: Submitted to Astronomy and Astrophysics. v1: 10 pages, 8 figures. v2:
corrected labels for the bibliographic references (no changes in the
bibliography). v3: revised version. 9 pages, 7 figures. Added a new figure.
Updated with a more realistic simulation for the interstellar dust and with
the latest cryogenic test
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