66 research outputs found
Phase effects due to beam misalignment on diffraction gratings
All-reflective interferometer configurations have been proposed for the next
generation of gravitational wave detectors, with diffractive elements replacing
transmissive optics. However, an additional phase noise creates more stringent
conditions for alignment stability. A framework for alignment stability with
the use of diffractive elements was required using a Gaussian model. We
successfully create such a framework involving modal decomposition to replicate
small displacements of the beam (or grating) and show that the modal model does
not contain the phase changes seen in an otherwise geometric planewave
approach. The modal decomposition description is justified by verifying
experimentally that the phase of a diffracted Gaussian beam is independent of
the beam shape, achieved by comparing the phase change between a zero-order and
first-order mode beam. To interpret our findings we employ a rigorous
time-domain simulation to demonstrate that the phase changes resulting from a
modal decomposition are correct, provided that the coordinate system which
measures the phase is moved simultaneously with the effective beam
displacement. This indeed corresponds to the phase change observed in the
geometric planewave model. The change in the coordinate system does not
instinctively occur within the analytical framework, and therefore requires
either a manual change in the coordinate system or an addition of the geometric
planewave phase factor.Comment: 14 pages, 8 figures, submitted to Optics Expres
Experimental demonstration of higher-order Laguerre-Gauss mode interferometry
The compatibility of higher-order Laguerre-Gauss (LG) modes with
interferometric technologies commonly used in gravitational wave detectors is
investigated. In this paper we present the first experimental results
concerning the performance of the LG33 mode in optical resonators. We show that
the Pound-Drever-Hall error signal for a LG33 mode in a linear optical
resonator is identical to that of the more commonly used LG00 mode, and
demonstrate the feedback control of the resonator with a LG33 mode. We
succeeded to increase the mode purity of a LG33 mode generated using a
spatial-light modulator from 51% to 99% upon transmission through a linear
optical resonator. We further report the experimental verification that a
triangular optical resonator does not transmit helical LG modes
Remarks on thermoelastic effects at low temperatures and quantum limits in displacement measurements
The noise level of thermoelastic fluctuations of a mirror at low temperature was derived and introduced by M. Cerdonio et al. [Phys. Rev. D 63, 082003 (2001)]. The importance of the paper has become remarkable according to the increasing attention to the low-temperature high-precision measurement device. Here we would like to introduce the analytical form of their equation of thermoelastic noise in the integral form in order to reduce the computational labor
Interferometers for Displacement-Noise-Free Gravitational-Wave Detection
We propose a class of displacement- and laser-noise free
gravitational-wave-interferometer configurations, which does not sense
non-geodesic mirror motions and laser noises, but provides non-vanishing
gravitational-wave signal. Our interferometer consists of 4 mirrors and 2
beamsplitters, which form 4 Mach-Zehnder interferometers. By contrast to
previous works, no composite mirrors are required. Each mirror in our
configuration is sensed redundantly, by at least two pairs of incident and
reflected beams. Displacement- and laser-noise free detection is achieved when
output signals from these 4 interferometers are combined appropriately. Our
3-dimensional interferometer configuration has a low-frequency response
proportional to f^2, which is better than the f^3 achievable by previous
2-dimensional configurations.Comment: 5 pages, 4 figure
Higher order Laguerre-Gauss mode degeneracy in realistic, high finesse cavities
Higher order Laguerre-Gauss (LG) beams have been proposed for use in future
gravitational wave detectors, such as upgrades to the Advanced LIGO detectors
and the Einstein Telescope, for their potential to reduce the effects of the
thermal noise of the test masses. This paper details the theoretical analysis
and simulation work carried out to investigate the behaviour of LG beams in
realistic optical setups, in particular the coupling between different LG modes
in a linear cavity. We present a new analytical approximation to compute the
coupling between modes, using Zernike polynomials to describe mirror surface
distortions. We apply this method in a study of the behaviour of the LG33 mode
within realistic arm cavities, using measured mirror surface maps from the
Advanced LIGO project. We show mode distortions that can be expected to arise
due to the degeneracy of higher order spatial modes within such cavities and
relate this to the theoretical analysis. Finally we identify the mirror
distortions which cause significant coupling from the LG33 mode into other
order 9 modes and derive requirements for the mirror surfaces.Comment: 12 pages Submitted to PRD 19/07/201
Residual amplitude modulation in interferometric gravitational wave detectors
The effects of residual amplitude modulation (RAM) in laser interferometers using heterodyne sensing can be substantial and difficult to mitigate. In this work, we analyze the effects of RAM on a complex laser interferometer used for gravitational wave detection. The RAM introduces unwanted offsets in the cavity length signals and thereby shifts the operating point of the optical cavities from the nominal point via feedback control. This shift causes variations in the sensing matrix, and leads to degradation in the performance of the precision noise subtraction scheme of the multiple-degree-of-freedom control system. In addition, such detuned optical cavities produce an optomechanical spring, which also perturbs the sensing matrix. We use our simulations to derive requirements on RAM for the Advanced LIGO (aLIGO) detectors, and show that the RAM expected in aLIGO will not limit its sensitivity
Diagonalizing sensing matrix of broadband RSE
For a broadband-operated RSE interferometer, a simple and smart length sensing and control scheme was newly proposed. The sensing matrix could be diagonal, owing to a simple allocation of two RF modulations and to a macroscopic displacement of cavity mirrors, which cause a detuning of the RF modulation sidebands. In this article, the idea of the sensing scheme and an optimization of the relevant parameters will be described
All-sky search for continuous gravitational waves from isolated neutron stars using Advanced LIGO and Advanced Virgo O3 data
We present results of an all-sky search for continuous gravitational waves which can be produced by spinning neutron stars with an asymmetry around their rotation axis, using data from the third observing run of the Advanced LIGO and Advanced Virgo detectors. Four different analysis methods are used to search in a gravitational-wave frequency band from 10 to 2048 Hz and a first frequency derivative from
−
10
−
8
to
10
−
9
 
 
Hz
/
s
. No statistically significant periodic gravitational-wave signal is observed by any of the four searches. As a result, upper limits on the gravitational-wave strain amplitude
h
0
are calculated. The best upper limits are obtained in the frequency range of 100 to 200 Hz and they are
∼
1.1
×
10
−
25
at 95% confidence level. The minimum upper limit of
1.10
×
10
−
25
is achieved at a frequency 111.5 Hz. We also place constraints on the rates and abundances of nearby planetary- and asteroid-mass primordial black holes that could give rise to continuous gravitational-wave signals
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