810 research outputs found
Opto-mechanical noise cancellation
The experiments presented in this thesis investigate the interaction between radiation and an optical cavity, in which one mirror of the cavity is mounted on a flexure which could be moved by radiation pressure. The cavity was shown to exhibit non-linear behaviour with high input power. The radiation pressure force was shown to change the mechanical resonance frequency of the moveable mirror. Motion was induced through amplitude modulation of a high power input beam and the extent of this motion measured using the cavity control loop. To demonstrate the way quantum correlations could be used to beat the SQL, the laser light incident on the cavity was prepared, using classical modulation techniques, with classical correlations between the quadratures that cause shot noise and radiation pressure noise. A level of modulation much higher than the quantum level was used to make the cancellation effects more visible. The effect of radiation pressure induced motion was cancelled by the addition of correlated frequency modulation. The input amplitude was then modulated by a white noise source. The resulting noise was partially cancelled when the same white noise source was used to drive the frequency modulator with a dierent phase. This cancellation demonstrably improved the signal to noise ratio of a signal injected into the system
The Influence of Dual-Recycling on Parametric Instabilities at Advanced LIGO
Laser interferometers with high circulating power and suspended optics, such
as the LIGO gravitational wave detectors, experience an optomechanical coupling
effect known as a parametric instability: the runaway excitation of a
mechanical resonance in a mirror driven by the optical field. This can saturate
the interferometer sensing and control systems and limit the observation time
of the detector. Current mitigation techniques at the LIGO sites are
successfully suppressing all observed parametric instabilities, and focus on
the behaviour of the instabilities in the Fabry-Perot arm cavities of the
interferometer, where the instabilities are first generated. In this paper we
model the full dual-recycled Advanced LIGO design with inherent imperfections.
We find that the addition of the power- and signal-recycling cavities shapes
the interferometer response to mechanical modes, resulting in up to four times
as many peaks. Changes to the accumulated phase or Gouy phase in the
signal-recycling cavity have a significant impact on the parametric gain, and
therefore which modes require suppression.Comment: 9 pages, 11 figures, 2 ancillary file
High dynamic range spatial mode decomposition
Accurate readout of low-power optical higher-order spatial modes is of
increasing importance to the precision metrology community. Mode sensors are
used to prevent mode mismatches from degrading quantum and thermal noise
mitigation strategies. Direct mode analysis sensors (MODAN) are a promising
technology for real-time monitoring of arbitrary higher-order modes. We
demonstrate MODAN with photo-diode readout to mitigate the typically low
dynamic range of CCDs. We look for asymmetries in the response our sensor to
break degeneracies in the relative alignment of the MODAN and photo-diode and
consequently improve the dynamic range of the mode sensor. We provide a
tolerance analysis and show methodology that can be applied for sensors beyond
first-order spatial modes
Cooling of a gram-scale cantilever flexure to 70 mK with a servo-modified optical spring
A series of recent articles have presented results demonstrating optical cooling of macroscopic objects,
highlighting the importance of this phenomenon for investigations of macroscopic quantum mechanics
and its implications for thermal noise in gravitational wave detectors. In this Letter, we present a
measurement of the off-resonance suspension thermal noise of a 1 g oscillator, and we show that it
can be cooled to just 70 mK. The cooling is achieved by using a servo to impose a phase delay between
oscillator motion and optical force. A model is developed to show how optical rigidity and optical cooling
can be interchangeable using this technique
Experimental demonstration of a classical analog to quantum noise cancellation for use in gravitational wave detection
We present results that are a classical analog to quantum noise cancellation. It is possible to breach the standard quantum limit in an interferometer by the use of squeezing to correlate orthogonal quadratures of quantum noise, causing their effects on the resulting sensitivity to cancel. A laser beam incident on a Fabry-Perot cavity was imprinted with classical, correlated noise in the same quadratures that cause shot noise and radiation pressure noise. Couplings between these quadratures due to a movable mirror, sensitive to radiation pressure, cause the excess classical noise to cancel. This cancellation was shown to improve the signal to noise ratio of an injected signal by approximately a factor of 10
Coating-free mirrors for high precision interferometric experiments
Thermal noise in mirror optical coatings may not only limit the sensitivity of future gravitational-wave detectors in their most sensitive frequency band but is also a major impediment for experiments that aim to reach the standard quantum limit or cool mechanical systems to their quantum ground state. We present the design and experimental characterization of a highly reflecting mirror without any optical coating. This coating-free mirror is based on total internal reflection and Brewster-angle coupling. In order to characterize its performance, the coating-free mirror was incorporated into a triangular ring cavity together with a high quality conventional mirror. The finesse of this cavity was measured using an amplitude transfer function to be about F≃4000. This finesse corresponds to a reflectivity of the coating-free mirror of about R≃99.89%. In addition, the dependence of the reflectivity on rotation was mapped out
Coating-free mirrors for high precision interferometric experiments
Thermal noise in mirror optical coatings may not only limit the sensitivity of future gravitational-wave
detectors in their most sensitive frequency band but is also a major impediment for experiments that aim to
reach the standard quantum limit or cool mechanical systems to their quantum ground state. We present the
design and experimental characterization of a highly reflecting mirror without any optical coating. This
coating-free mirror is based on total internal reflection and Brewster-angle coupling. In order to characterize its
performance, the coating-free mirror was incorporated into a triangular ring cavity together with a high quality
conventional mirror. The finesse of this cavity was measured using an amplitude transfer function to be about
F 4000. This finesse corresponds to a reflectivity of the coating-free mirror of about R 99.89%. In addition,
the dependence of the reflectivity on rotation was mapped out
Sensors and Actuators for the Advanced LIGO+ Upgrade
Advanced Laser Interferometer Gravitational-wave Observatory (LIGO A+) is a major upgrade to LIGO—the Laser Interferometer Gravitational-wave Observatory. For the A+ project, we have developed, produced, and characterized sensors and electronics to interrogate new optical suspensions designed to isolate optics from vibrations. The central element is a displacement sensor with an integrated electromagnetic actuator known as a BOSEM (Birmingham Optical Sensor and ElectroMagnetic actuator) and its readout and drive electronics required to integrate them into LIGO’s control and data system. In this paper, we report on the improvements to the sensors and the testing procedures undertaken to meet the enhanced performance requirements set out by the A+ upgrade to the detectors. The best devices reach a noise level of 4.5 ×10−11m/√Hz at a measurement frequency of 1 Hz, an improvement of 6.7 times over standard devices
Passive-performance, analysis, and upgrades of a 1-ton seismic attenuation system
The 10m Prototype facility at the Albert-Einstein-Institute (AEI) in Hanover,
Germany, employs three large seismic attenuation systems to reduce mechanical
motion. The AEI Seismic-Attenuation-System (AEI-SAS) uses mechanical
anti-springs in order to achieve resonance frequencies below 0.5Hz. This system
provides passive isolation from ground motion by a factor of about 400 in the
horizontal direction at 4Hz and in the vertical direction at 9Hz. The presented
isolation performance is measured under vacuum conditions using a combination
of commercial and custom-made inertial sensors. Detailed analysis of this
performance led to the design and implementation of tuned dampers to mitigate
the effect of the unavoidable higher order modes of the system. These dampers
reduce RMS motion substantially in the frequency range between 10 and 100Hz in
6 degrees of freedom. The results presented here demonstrate that the AEI-SAS
provides substantial passive isolation at all the fundamental mirror-suspension
resonances
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