2,568 research outputs found
Angular instability due to radiation pressure in the LIGO gravitational-wave detector
We observed the effect of radiation pressure on the angular sensing and control system of the Laser Interferometer Gravitational-Wave Observatory (LIGO) interferometer’s core optics at LIGO Hanford Observatory. This is the first measurement of this effect in a complete gravitational-wave interferometer. Only one of the two angular modes survives with feedback control, because the other mode is suppressed when the control gain is sufficiently large. We developed a mathematical model to understand the physics of the system. This model matches well with the dynamics that we observe
Probing microplasticity in small scale FCC crystals via Dynamic Mechanical Analysis
In small-scale metallic systems, collective dislocation activity has been
correlated with size effects in strength and with a step-like plastic response
under uniaxial compression and tension. Yielding and plastic flow in these
samples is often accompanied by the emergence of multiple dislocation
avalanches. Dislocations might be active pre-yield, but their activity
typically cannot be discerned because of the inherent instrumental noise in
detecting equipment. We apply Alternate Current (AC) load perturbations via
Dynamic Mechanical Analysis (DMA) during quasi-static uniaxial compression
experiments on single crystalline Cu nano-pillars with diameters of 500 nm, and
compute dynamic moduli at frequencies 0.1, 0.3, 1, and 10 Hz under
progressively higher static loads until yielding. By tracking the collective
aspects of the oscillatory stress-strain-time series in multiple samples, we
observe an evolving dissipative component of the dislocation network response
that signifies the transition from elastic behavior to dislocation avalanches
in the globally pre-yield regime. We postulate that microplasticity, which is
associated with the combination of dislocation avalanches and slow viscoplastic
relaxations, is the cause of the dependency of dynamic modulus on the driving
rate and the quasi-static stress. We construct a continuum mesoscopic
dislocation dynamics model to compute the frequency response of stress over
strain and obtain a consistent agreement with experimental observations. The
results of our experiments and simulations present a pathway to discern and
quantify correlated dislocation activity in the pre-yield regime of deforming
crystals.Comment: 5 pages, 3 figure
Towards the Laboratory Search for Space-Time Dissipation
It has been speculated that gravity could be an emergent phenomenon, with
classical general relativity as an effective, macroscopic theory, valid only
for classical systems at large temporal and spatial scales. As in classical
continuum dynamics, the existence of underlying microscopic degrees of freedom
may lead to macroscopic dissipative behaviors. With the hope that such
dissipative behaviors of gravity could be revealed by carefully designed
experiments in the laboratory, we consider a phenomenological model that adds
dissipations to the gravitational field, much similar to frictions in solids
and fluids. Constraints to such dissipative behavior can already be imposed by
astrophysical observations and existing experiments, but mostly in lower
frequencies. We propose a series of experiments working in higher frequency
regimes, which may potentially put more stringent bounds on these models.Comment: 18 pages, 8 figure
A New Bound on Excess Frequency Noise in Second Harmonic Generation in PPKTP at the 10^-19 Level
We report a bound on the relative frequency fluctuations in nonlinear second
harmonic generation. A 1064nm Nd:YAG laser is used to read out the phase of a
Mach-Zehnder interferometer while PPKTP, a nonlinear crystal, is placed in each
arm to generate second harmonic light. By comparing the arm length difference
of the Mach Zehnder as read out by the fundamental 1064 nm light, and its
second harmonic at 532 nm, we can bound the excess frequency noise introduced
in the harmonic generation process. We report an amplitude spectral density of
frequency noise with total RMS frequency deviation of 3mHz and a minimum value
of 20 {\mu}Hz/rtHz over 250 seconds with a measurement bandwidth of 128 Hz,
corresponding to an Allan deviation of 10^-19 at 20 seconds.Comment: Submitted to Optics Express June 201
Characterization of transient noise in Advanced LIGO relevant to gravitational wave signal GW150914
On 14 September 2015, a gravitational wave signal from a coalescing black hole binary system was observed by the Advanced LIGO detectors. This paper describes the transient noise backgrounds used to determine the significance of the event (designated GW150914) and presents the results of investigations into potential correlated or uncorrelated sources of transient noise in the detectors around the time of the event. The detectors were operating nominally at the time of GW150914. We have ruled out environmental influences and non-Gaussian instrument noise at either LIGO detector as the cause of the observed gravitational wave signal
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
Novel cloning machine with supplementary information
Probabilistic cloning was first proposed by Duan and Guo. Then Pati
established a novel cloning machine (NCM) for copying superposition of multiple
clones simultaneously. In this paper, we deal with the novel cloning machine
with supplementary information (NCMSI). For the case of cloning two states, we
demonstrate that the optimal efficiency of the NCMSI in which the original
party and the supplementary party can perform quantum communication equals that
achieved by a two-step cloning protocol wherein classical communication is only
allowed between the original and the supplementary parties. From this
equivalence it follows that NCMSI may increase the success probabilities for
copying. Also, an upper bound on the unambiguous discrimination of two
nonorthogonal pure product states is derived. Our investigation generalizes and
completes the results in the literature.Comment: 22 pages; the presentation is revised, and some typos are correcte
Brownian Thermal Noise in Multilayer Coated Mirrors
We analyze the Brownian thermal noise of a multi-layer dielectric coating,
used in high-precision optical measurements including interferometric
gravitational-wave detectors. We assume the coating material to be isotropic,
and therefore study thermal noises arising from shear and bulk losses of the
coating materials. We show that coating noise arises not only from layer
thickness fluctuations, but also from fluctuations of the interface between the
coating and substrate, driven by internal fluctuating stresses of the coating.
In addition, the non-zero photoeleastic coefficients of the thin films modifies
the influence of the thermal noise on the laser field. The thickness
fluctuations of different layers are statistically independent, however, there
exists a finite coherence between layers and the substrate-coating interface.
Taking into account uncertainties in material parameters, we show that
significant uncertainties still exist in estimating coating Brownian noise.Comment: 26 pages, 18 figure
GW151226: Observation of Gravitational Waves from a 22-Solar-Mass Binary Black Hole Coalescence
We report the observation of a gravitational-wave signal produced by the coalescence of two stellar-mass black holes. The signal, GW151226, was observed by the twin detectors of the Laser Interferometer Gravitational-Wave Observatory (LIGO) on December 26, 2015 at 03: 38: 53 UTC. The signal was initially identified within 70 s by an online matched-filter search targeting binary coalescences. Subsequent off-line analyses recovered GW151226 with a network signal-to-noise ratio of 13 and a significance greater than 5 sigma. The signal persisted in the LIGO frequency band for approximately 1 s, increasing in frequency and amplitude over about 55 cycles from 35 to 450 Hz, and reached a peak gravitational strain of 3.4(-0.9)(+0.7) x 10(-22). The inferred source-frame initial black hole masses are 14.2(-3.7)(+8.3) M-circle dot and 7.5(-2.3)(+2.3) M-circle dot, and the final black hole mass is 20.8(-1.7)(+6.1) M-circle dot. We find that at least one of the component black holes has spin greater than 0.2. This source is located at a luminosity distance of 440(-190)(+180) Mpc corresponding to a redshift of 0.09(-0.04)(+0.03). All uncertainties define a 90% credible interval. This second gravitational-wave observation provides improved constraints on stellar populations and on deviations from general relativity
Measurement of mechanical losses in the carbon nanotube black coating of silicon wafers
The successful detection of gravitational waves from astrophysical sources carried out by the laser interferometric detectors LIGO and Virgo have stimulated scientists to develop a new generation of more sensitive gravitational wave detectors. In the proposed upgrade called LIGO Voyager, silicon test masses will be cooled to cryogenic temperatures. To provide heat removal from the test masses when they absorb the laser light one can increase their thermal emissivity using a special black coating. We have studied mechanical losses in a carbon nanotube black coating deposited on silicon wafers. The additional thermal noise associated with mechanical loss in this coating was calculated using a value of the product of the coating Young's modulus and the coating mechanical loss angle determined from the measurements. It was found that at temperatures of about 123 K, the additional thermal noise of the LIGO Voyager test mass caused by the carbon nanotube black coating deposited on its barrel is less than the noise associated with the Acktar Black coating and is 20 times less than the noise due to the optical high reflective (HR) coating of the test mass
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