395 research outputs found
An analysis and visualization of the output mode-matching requirements for squeezing in Advanced LIGO and future gravitational wave detectors
The sensitivity of ground-based gravitational wave (GW) detectors will be
improved in the future via the injection of frequency-dependent squeezed
vacuum. The achievable improvement is ultimately limited by losses of the
interferometer electromagnetic field that carries the GW signal. The analysis
and reduction of optical loss in the GW signal chain will be critical for
optimal squeezed light-enhanced interferometry. In this work we analyze a
strategy for reducing output-side losses due to spatial mode mismatch between
optical cavities with the use of adaptive optics. Our goal is not to design a
detector from the top down, but rather to minimize losses within the current
design. Accordingly, we consider actuation on optics already present and one
transmissive optic to be added between the signal recycling mirror and the
output mode cleaner. The results of our calculation show that adaptive
mode-matching with the current Advanced LIGO design is a suitable strategy for
loss reduction that provides less than 2% mean output mode-matching loss. The
range of actuation required is +47 uD on SR3, +140 mD on OM1 and OM2, +50 mD on
the SRM substrate, and -50 mD on the added new transmissive optic. These
requirements are within the demonstrated ranges of real actuators in similar or
identical configurations to the proposed implementation. We also present a
novel technique that graphically illustrates the matching of interferometer
modes and allows for a quantitative comparison of different combinations of
actuators.Comment: Matches version accepted in PR
Analytical model for ring heater thermal compensation in the Advanced Laser Interferometer Gravitational-wave Observatory
Advanced laser interferometer gravitational-wave detectors use high laser power to achieve design sensitivity. A small part of this power is absorbed in the interferometer cavity mirrors where it creates thermal lenses, causing aberrations in the main laser beam that must be minimized by the actuation of “ring heaters,” which are additional heater elements that are aimed to reduce the temperature gradients in the mirrors. In this article we derive the first, to the best of our knowledge, analytical model of the temperature field generated by an ideal ring heater. We express the resulting optical aberration contribution to the main laser beam in this axisymmetric case. Used in conjunction with wavefront measurements, our model provides a more complete understanding of the thermal state of the cavity mirrors and will allow a more efficient use of the ring heaters in the Advanced Laser Interferometer Gravitational-wave Observatory
Thermal modelling of Advanced LIGO test masses
High-reflectivity fused silica mirrors are at the epicentre of current
advanced gravitational wave detectors. In these detectors, the mirrors interact
with high power laser beams. As a result of finite absorption in the high
reflectivity coatings the mirrors suffer from a variety of thermal effects that
impact on the detectors performance. We propose a model of the Advanced LIGO
mirrors that introduces an empirical term to account for the radiative heat
transfer between the mirror and its surroundings. The mechanical mode frequency
is used as a probe for the overall temperature of the mirror. The thermal
transient after power build-up in the optical cavities is used to refine and
test the model. The model provides a coating absorption estimate of 1.5 to 2.0
ppm and estimates that 0.3 to 1.3 ppm of the circulating light is scattered on
to the ring heater.Comment: 14 pages, 9 figure
Effects of mirror birefringence and its fluctuations to laser interferometric gravitational wave detectors
Crystalline materials are promising candidates as substrates or
high-reflective coatings of mirrors to reduce thermal noises in future laser
interferometric gravitational wave detectors. However, birefringence of such
materials could degrade the sensitivity of gravitational wave detectors, not
only because it can introduce optical losses, but also because its fluctuations
create extra phase noise in the arm cavity reflected beam. In this paper, we
analytically estimate the effects of birefringence and its fluctuations in the
mirror substrate and coating for gravitational wave detectors. Our calculations
show that the requirements for the birefringence fluctuations in silicon
substrate and AlGaAs coating will be on the order of and
rad/ at 100~Hz, respectively, for future gravitational wave
detectors. We also point out that optical cavity response needs to be carefully
taken into account to estimate optical losses from depolarization.Comment: 11 pages, 4 figure
In-situ characterization of the thermal state of resonant optical interferometers via tracking of their higher-order mode resonances
Thermal lensing in resonant optical interferometers such as those used for
gravitational wave detection is a concern due to the negative impact on control
signals and instrument sensitivity. In this paper we describe a method for
monitoring the thermal state of such interferometers by probing the
higher-order spatial mode resonances of the cavities within them. We
demonstrate the use of this technique to measure changes in the Advanced LIGO
input mode cleaner cavity geometry as a function of input power, and
subsequently infer the optical absorption at the mirror surfaces at the level
of 1 ppm per mirror. We also demonstrate the generation of a useful error
signal for thermal state of the Advanced LIGO power recycling cavity by
continuously tracking the first order spatial mode resonance frequency. Such an
error signal could be used as an input to thermal compensation systems to
maintain the interferometer cavity geometries in the presence of transients in
circulating light power levels, thereby maintaining optimal sensitivity and
maximizing the duty-cycle of the detectors
Enhancing the dynamic range of deformable mirrors with compression bias
We report the design and testing of a compression-biased thermally-actuated deformable mirror that has a dynamic range larger than the limit imposed by pure-bending stress, negligible higher-order-mode scattering, and a linear defocus response and that is vacuum compatible. The optimum design principles for this class of actuator are described and a mirror with 370 mD dynamic range is demonstrated
Multi-color Cavity Metrology
Long baseline laser interferometers used for gravitational wave detection
have proven to be very complicated to control. In order to have sufficient
sensitivity to astrophysical gravitational waves, a set of multiple coupled
optical cavities comprising the interferometer must be brought into resonance
with the laser field. A set of multi-input, multi-output servos then lock these
cavities into place via feedback control. This procedure, known as lock
acquisition, has proven to be a vexing problem and has reduced greatly the
reliability and duty factor of the past generation of laser interferometers. In
this article, we describe a technique for bringing the interferometer from an
uncontrolled state into resonance by using harmonically related external fields
to provide a deterministic hierarchical control. This technique reduces the
effect of the external seismic disturbances by four orders of magnitude and
promises to greatly enhance the stability and reliability of the current
generation of gravitational wave detector. The possibility for using
multi-color techniques to overcome current quantum and thermal noise limits is
also discussed
Mid-IR laser for wavefront correction in gravitational wave detectors
The next-generation gravitational wave detectors aim to enhance our understanding of extreme phenomena in the Universe. The high-frequency sensitivity of these detectors will be maximized by injecting squeezed vacuum states into the detector. However, the performance advantages offered by squeezed state injection can be easily degraded by losses in the system. A significant source of loss is the mode mismatch between optical cavities within the interferometer. To overcome this issue, new actuators are required that can produce a highly spherical wavefront change, with minimal higher order aberrations, whist adding low phase noise to the incident beam
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