28 research outputs found
Coherent Cancellation of Photothermal Noise in GaAs/AlGaAs Bragg Mirrors
Thermal noise is a limiting factor in many high-precision optical
experiments. A search is underway for novel optical materials with reduced
thermal noise. One such pair of materials, gallium arsenide and
aluminum-alloyed gallium arsenide (collectively referred to as AlGaAs), shows
promise for its low Brownian noise when compared to conventional materials such
as silica and tantala. However, AlGaAs has the potential to produce a high
level of thermo-optic noise. We have fabricated a set of AlGaAs crystalline
coatings, transferred to fused silica substrates, whose layer structure has
been optimized to reduce thermo-optic noise by inducing coherent cancellation
of the thermoelastic and thermorefractive effects. By measuring the
photothermal transfer function of these mirrors, we find evidence that this
optimization has been successful.Comment: 10 pages, 7 figure
Quantum Backaction Cancellation in the Audio Band
We report on the cancellation of quantum backaction noise in an optomechanical cavity. We perform measurements of the displacement of the microresonator, one in reflection of the cavity and one in transmission of the cavity. We show that measuring the amplitude quadrature of the light transmitted by the optomechanical cavity allows us to cancel the backaction noise between 2 and 50 kHz as a consequence of the strong optical spring present in the detuned cavity. This cancellation yields a more sensitive measurement of the microresonator’s position with a 2 dB increase in sensitivity. To confirm that the backaction is eliminated, we measure the noise in the transmission signal as a function of circulating power and use a correlation technique between two photodetectors to remove shot noise. Remaining backaction noise would be observable as a power-dependent noise floor, which is not observed. Eliminating the effects of backaction in this frequency regime is an important demonstration of a technique that could be used to mitigate the effects of backaction in interferometric gravitational wave detectors such as Advanced LIGO, VIRGO, and KAGRA
Quantum Backaction Cancellation in the Audio Band
We report on the cancellation of quantum backaction noise in an optomechanical cavity. We perform measurements of the displacement of the microresonator, one in reflection of the cavity and one in transmission of the cavity. We show that measuring the amplitude quadrature of the light transmitted by the optomechanical cavity allows us to cancel the backaction noise between 2 and 50 kHz as a consequence of the strong optical spring present in the detuned cavity. This cancellation yields a more sensitive measurement of the microresonator’s position with a 2 dB increase in sensitivity. To confirm that the backaction is eliminated, we measure the noise in the transmission signal as a function of circulating power and use a correlation technique between two photodetectors to remove shot noise. Remaining backaction noise would be observable as a power-dependent noise floor, which is not observed. Eliminating the effects of backaction in this frequency regime is an important demonstration of a technique that could be used to mitigate the effects of backaction in interferometric gravitational wave detectors such as Advanced LIGO, VIRGO, and KAGRA
Simultaneously-Measured Mid-Infrared Refractive Indices of GaAs/AlGaAs
We present our results for a simultaneous measurement of the refractive
indices of Gallium Arsenide (GaAs) and Aluminum Gallium Arsenide
(AlGaAs) in the spectral region from to
( to ). These
values are obtained from a monocrystalline thin-film multilayer Bragg mirror of
excellent purity (background doping ), grown via molecular beam epitaxy. To recover the
refractive indices over such a broad wavelength range, we fit a dispersion
model for each material. For that, we measure both a photometrically accurate
transmittance spectrum of the Bragg mirror via Fourier-transform infrared
spectrometry and the individual physical layer thicknesses of the structure via
scanning electron microscopy. To infer the uncertainty of the refractive index
values, we estimate relevant measurement uncertainties and propagate them via a
Monte-Carlo-type method. This method conclusively yields propagated relative
uncertainties on the order of over the measured spectral range for
both GaAs and AlGaAs. The fitted model can also approximate
the refractive index for MBE-grown AlGaAs for . These updated values will be essential in the design and
fabrication of next-generation active and passive optical devices in a spectral
region which is of high interest in many fields, e.g., laser design and
cavity-enhanced spectroscopy.Comment: 20 pages, 5 figures, submitted to PR