Amorphous silicon has ideal properties for many applications in fundamental research and industry. However, the optical absorption is often unacceptably high, particularly for gravitational-wave ...detection. We report a novel ion-beam deposition method for fabricating amorphous silicon with unprecedentedly low unpaired electron-spin density and optical absorption, the spin limit on absorption being surpassed for the first time. At low unpaired electron density, the absorption is no longer correlated with electron spins, but with the electronic mobility gap. Compared to standard ion-beam deposition, the absorption at 1550 nm is lower by a factor of ≈100. This breakthrough shows that amorphous silicon could be exploited as an extreme performance optical coating in near-infrared applications, and it represents an important proof of concept for future gravitational-wave detectors.
Precision interferometry is the leading method for extremely sensitive measurements in gravitational wave astronomy. Thermal noise of dielectric coatings poses a limitation to the sensitivity of ...these interferometers. To decrease coating thermal noise, new crystalline GaAs/AlGaAs multilayer mirrors have been developed. To date, the surface figure and thickness uniformity of these alternative low-loss coatings has not been investigated. Surface figure errors, for example, cause small angle scattering and thereby limit the sensitivity of an interferometer. Here we measure the surface figure of highly reflective, substrate-transferred, crystalline GaAs/AlGaAs coatings with a custom scanning reflectance system. We exploit the fact that the reflectivity varies with the thickness of the coating. To increase penetration into the coating, we used a 1550 nm laser on a highly reflective coating designed for a center wavelength of 1064 nm. The RMS thickness variation of a two inch optic was measured to be 0.41 ± 0.05 nm. This result is within 10% of the thickness uniformity, of 0.37 nm RMS, achieved with ion-beam sputtered coatings for the aLIGO detector. We additionally measured a lower limit of the laser induced damage threshold of 64 MW/cm
for GaAs/AlGaAs coatings at a wavelength of 1064 nm.
The detection of gravitational waves from compact binary mergers by LIGO has opened the era of gravitational wave astronomy, revealing a previously hidden side of the cosmos. To maximize the reach of ...the existing LIGO observatory facilities, we have designed a new instrument able to detect gravitational waves at distances 5 times further away than possible with Advanced LIGO, or at greater than 100 times the event rate. Observations with this new instrument will make possible dramatic steps toward understanding the physics of the nearby Universe, as well as observing the Universe out to cosmological distances by the detection of binary black hole coalescences. This article presents the instrument design and a quantitative analysis of the anticipated noise floor.
The words "
No
" and
"Yes
" are involved in conditioning to prohibit or encourage behavior, respectively. The authors, therefore, hypothesized that these words would be attributed to endogenous ...valence, activating neuronal circuits involved with valence and emotional control. Functional MRI (fMRI) at 4 Tesla was used to record regional brain activity while participants were exposed to emphatic vocalizations of the words. Results showed that
No
and
Yes
were associated with opposite brain-behavior responses; while
No
was negatively valenced, produced slower response times, and evoked a negative signal in the right lateral orbitofrontal cortex (OFC),
Yes
was positively valenced, produced faster response times, and evoked a positive signal in a contiguous region of the OFC. Attribution of negative valence to
No
and trait anger control were associated with increased responsivity of the OFC to
No
. Inasmuch as sensitivity to the prohibitive command
No
develops during childhood through interaction with primary caregivers as the first social objects, our findings may implicate the lateral OFC in the neurobiology of emotion regulation and subsequent social development.
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