49 research outputs found
Overview of the LISA mission and R&D developments at the APC
International audienceThe study of the gravitational waves opens a new window for the observation of the universe. Completing the observations obtained from electro-magnetic waves, neutrinos and cosmic rays, the gravitational waves will provide informations on the most violent phenomena in the universe, as supernova explosions, collisions of binary systems or mergers of black holes. Their study will thus increase our knowledge in astrophysics, but also in cosmology and fundamental physics. This paper will make a short presentation of the future space interferometer LISA, aiming at detecting gravitational waves, and presents an overview of the R&D developments for LISA at the APC laboratory
LISA ON TABLE: AN OPTICAL SIMULATOR FOR LISA
LISA, the first space project for detecting gravitational waves, relies on two main technical challenges: the free falling masses and an outstanding precision on phase shift measurements (a few pm on 5 Mkm in the LISA band). The technology of the free falling masses, i.e. their isolation to forces other than gravity and the capability for the spacecraft to precisely follow the test masses, will soon be tested with the technological LISA Pathfinder mission. The performance of the phase measurement will be achieved by at least two stabilization stages: a pre-stabilisation of the laser frequency at a level of 10-13 (relative frequency stability) will be further improved by using numerical algorithms, such as Time Delay Interferometry, which have been theoretically and numerically demonstrated to reach the required performance level (10-21). Nevertheless, these algorithms, though already tested with numerical model of LISA, require experimental validation, including 'realistic' hardware elements. Such an experiment would allow to evaluate the expected noise level and the possible interactions between subsystems. To this end, the APC is currently developing an optical benchtop experiment, called LISA On Table (LOT), which is representative of the three LISA spacecraft. A first module of the LOT experiment has been mounted and is being characterized. After completion this facility may be used by the LISA community to test hardware (photodiodes, phasemeters) or software (reconstruction algorithms) components
Emission-lines calibrations of the Star Formation Rate from the Sloan Digital Sky Survey
Our goal is to study the existing star formation rate calibrations based on
emission-line luminosities and to provide new ones. We use the SDSS data
release DR4, which gives star formation rates and emission-line luminosities of
more than 100000 star-forming galaxies. We confirm that the best results are
obtained with the Halpha calibration. This calibration has an uncertainty of
0.17 dex. We show that one has to check carefully the method used to derive the
dust attenuation and to use the adequate calibration: in some cases, the
standard scaling law has to be replaced by a more general power law. When data
is corrected for dust attenuation but the Halpha emission line not observed,
the use of the Hbeta emission line, has to be preferred to the [OII]3727
emission line. In the case of uncorrected data, the correction for dust
attenuation can be assumed as a constant value but we show that such method
leads to poor results, in terms of dispersion and residual slope.
Self-consistent corrections, based e.g. on the absolute magnitude, give better
results in terms of dispersion but still suffer from systematic shifts, and/or
residual slopes. The best results with data not corrected for dust attenuation
are obtained when using the observed [OII]3727 and Hbeta emission lines
together. This calibration has an uncertainty of 0.23 dex
Quantum cascade laser frequency stabilisation at the sub-Hz level
Quantum Cascade Lasers (QCL) are increasingly being used to probe the
mid-infrared "molecular fingerprint" region. This prompted efforts towards
improving their spectral performance, in order to reach ever-higher resolution
and precision. Here, we report the stabilisation of a QCL onto an optical
frequency comb. We demonstrate a relative stability and accuracy of 2x10-15 and
10-14, respectively. The comb is stabilised to a remote near-infrared
ultra-stable laser referenced to frequency primary standards, whose signal is
transferred via an optical fibre link. The stability and frequency traceability
of our QCL exceed those demonstrated so far by two orders of magnitude. As a
demonstration of its capability, we then use it to perform high-resolution
molecular spectroscopy. We measure absorption frequencies with an 8x10-13
relative uncertainty. This confirms the potential of this setup for ultra-high
precision measurements with molecules, such as our ongoing effort towards
testing the parity symmetry by probing chiral species
DYNAMO - I. A sample of H alpha-luminous galaxies with resolved kinematics
DYNAMO is a multiwavelength, spatially resolved survey of local (z ⌠0.1) star-forming galaxies designed to study evolution through comparison with samples at z _ 2. Half of the sample has integrated Hα luminosities of >1042 erg sâ1, the typical lower limit for resolved spectroscopy at z _ 2. The sample covers a range in stellar mass (109â1011M_) and star formation rate (0.2â100M_ yrâ1). In this first paper of a series, we present integral-field spectroscopy of Hα emission for the sample of 67 galaxies. We infer gas fractions in our sample as high as _0.8, higher than typical for local galaxies. Gas fraction correlates with stellarmass in galaxies with star formation rates below 10M_ yrâ1, as found by COLDGASS, but galaxies with higher star formation rates have higher than expected gas fractions. There is only a weak correlation, if any, between gas fraction and gas velocity dispersion. Galaxies in the sample visually classified as disc-like are offset from the local stellar mass TullyâFisher relation to higher circular velocities, but this offset vanishes when both gas and stars are included in the baryonic TullyâFisher relation. The mean gas velocity dispersion of the sample is_50 km sâ1, and V/Ï ranges from 2 to 10 for most of the discs, similar to âturbulentâ galaxies at high redshift. Half of our sample show disc-like rotation, while âŒ20 per cent show no signs of rotation. The division between rotating and non-rotating is approximately equal for the sub-samples with either star formation rates >10M_ yrâ1, or specific star formation rates typical of the star formation âmain sequenceâ at z _ 2. Across our whole sample, we find good correlation between the dominance of âturbulenceâ in galaxy discs (as expressed by V/Ï ) and gas fraction as has been predicted for marginally stable Toomre discs. Comparing our sample with many others at low- and high-redshift reveals a correlation between gas velocity dispersion and star formation rate. These findings suggest the DYNAMO discs are excellent candidates for local galaxies similar to turbulent z _ 2 disc galaxies
AD-7/GBAR status report for the 2021 CERN SPSC
We report on the activities performed during 2019-2020 and the plans for 2021 for the GBAR experiment
Low frequency noise fiber delay stabilized laser with reduced sensitivity to acceleration
International audienceLasers with sub-hertz line-width and fractional frequency instability around 1Ă10-15 for 0.1 s to 10 s averaging time are currently realized by locking onto an ultra-stable Fabry-Perot cavity using the Pound-Drever-Hall method. This powerful method requires tight alignment of free space optical components, precise polarization adjustment and spatial mode matching. To circumvent these issues, we use an all-fiber Michelson interferometer with a long fiber spool as a frequency reference and a heterodyne detection technique with a fibered acousto optical modulator (AOM)1. At low Fourier frequencies, the frequency noise of our system is mainly limited by mechanical vibrations, an issue that has already been explored in the field of optoelectronic oscillators.2,3,4</SUP
Low frequency noise fiber delay stabilized laser with reduced sensitivity to acceleration
International audienceLasers with sub-hertz line-width and fractional frequency instability around 1Ă10-15 for 0.1 s to 10 s averaging time are currently realized by locking onto an ultra-stable Fabry-Perot cavity using the Pound-Drever-Hall method. This powerful method requires tight alignment of free space optical components, precise polarization adjustment and spatial mode matching. To circumvent these issues, we use an all-fiber Michelson interferometer with a long fiber spool as a frequency reference and a heterodyne detection technique with a fibered acousto optical modulator (AOM)1. At low Fourier frequencies, the frequency noise of our system is mainly limited by mechanical vibrations, an issue that has already been explored in the field of optoelectronic oscillators.2,3,4</SUP
Molecular laser stabilization at low frequencies for the LISA mission
We have developed a 532 nm iodine stabilized laser system that may be suitable for the LISA mission (Laser Interferometer Space Antenna) or other future spaceborne missions. This system is based on an externally frequency-doubled Nd:YAG laser source and uses the molecular transfer spectroscopy technique for the frequency stabilization. This technique has been optimized for LISA: compactness (less than 1.1Ă1.1m2), vacuum compatibility, ease of use and initialization, minimization of the number of active components (acousto-optic modulators are both used for frequency shifting and phase modulating the pump beam). By locking on the a10 hyperfine component of the R(56)32-0 transition, we find an Allan standard deviation (Ï) of 3Ă10-14 at 1 s and Ï<2Ă10-14 for 20sâ€Ïâ€103s. In terms of linear spectral density, this roughly corresponds to a stability better than 30Hz/Hz between 10-2 and 1 Hz with a stability decrease close to 1/f below 10 mHz