664 research outputs found
Kiri Koburgi õukonnateatri näitleja Ramaizinski'le
Burmeister, Friedrich, 1771-1851, näitleja DresdenisPalub olla eestkostjaks noorele, algajale näitlejal
Realization of a monolithic high-reflectivity cavity mirror from a single silicon crystal
We report on the first experimental realization of a high-reflectivity cavity
mirror that solely consists of a single silicon crystal. Since no material was
added to the crystal, the urgent problem of 'coating thermal noise' that
currently limits classical as well as quantum measurements is avoided. Our
mirror is based on a surface nanostructure that creates a resonant surface
waveguide. In full agreement with a rigorous model we realized a reflectivity
of (99.79+/-0.01)% at a wavelength of 1.55 {\mu}m, and achieved a cavity
finesse of 2784. We anticipate that our achievement will open the avenue to
next generation high-precision experiments targeting fundamental questions of
physics.Comment: Phys. Rev. Lett., accepte
Diffractively coupled Fabry-Perot resonator with power-recycling
We demonstrate the optical coupling of two cavities without light
transmission through a substrate. Compared to a conventional coupling
component, that is a partially transmissive mirror, an all-reflective coupler
avoids light absorption in the substrate and therefore associated thermal
problems, and even allows the use of opaque materials with possibly favourable
mechanical and thermal properties. Recently, the all-reflective coupling of two
cavities with a low-efficiency 3-port diffraction grating was theoretically
investigated. Such a grating has an additional (a third) port. However, it was
shown that the additional port does not necessarily decrease the bandwidth of
the coupled cavities. Such an all-reflective scheme for cavity coupling is of
interest in the field of gravitational wave detection. In such detectors light
that is resonantly enhanced inside the so-called power-recycling cavity is
coupled to (kilometre-scale) Fabry-Perot resonators representing the arms of a
Michelson interferometer. In order to achieve a high sensitivity over a broad
spectrum, the Fabry-Perot resonators need to have a high bandwidth for a given
(high) power build-up. We realized such an all-reflective coupling in a
table-top experiment. Our findings are in full agreement with the theoretical
model incorporating the characteristics of the 3-port grating used, and
therefore encourage the application of all-reflective cavity couplers in future
gravitational wave detectors
Digital Twin of the Radio Environment: A Novel Approach for Anomaly Detection in Wireless Networks
The increasing relevance of resilience in wireless connectivity for Industry
4.0 stems from the growing complexity and interconnectivity of industrial
systems, where a single point of failure can disrupt the entire network,
leading to significant downtime and productivity losses. It is thus essential
to constantly monitor the network and identify any anomaly such as a jammer.
Hereby, technologies envisioned to be integrated in 6G, in particular joint
communications and sensing (JCAS) and accurate indoor positioning of
transmitters, open up the possibility to build a digital twin (DT) of the radio
environment. This paper proposes a new approach for anomaly detection in
wireless networks enabled by such a DT which allows to integrate contextual
information on the network in the anomaly detection procedure. The basic
approach is thereby to compare expected received signal strengths (RSSs) from
the DT with measurements done by distributed sensing units (SUs). Employing
simulations, different algorithms are compared regarding their ability to infer
from the comparison on the presence or absence of an anomaly, particular a
jammer. Overall, the feasibility of anomaly detection using the proposed
approach is demonstrated which integrates in the ongoing research on employing
DTs for comprehensive monitoring of wireless networks.Comment: 6 pages, 4 figure
High reflectivity grating waveguide coatings for 1064nm
We propose thin single-layer grating waveguide structures to be used as
high-reflectivity, but low thermal noise, alternative to conventional coatings
for gravitational wave detector test mass mirrors. Grating waveguide (GWG)
coatings can show a reflectivity of up to 100% with an overall thickness of
less than a wavelength. We theoretically investigate GWG coatings for 1064nm
based on tantala (Ta2O5) on a Silica substrate focussing on broad spectral
response and low thickness
All-reflective coupling of two optical cavities with 3-port diffraction gratings
The shot-noise limited sensitivity of Michelson-type laser interferometers
with Fabry-Perot arm cavities can be increased by the so-called power-recycling
technique. In such a scheme the power-recycling cavity is optically coupled
with the interferometer's arm cavities. A problem arises because the central
coupling mirror transmits a rather high laser power and may show thermal
lensing, thermo-refractive noise and photo-thermo-refractive noise. Cryogenic
cooling of this mirror is also challenging, and thus thermal noise becomes a
general problem. Here, we theoretically investigate an all-reflective coupling
scheme of two optical cavities based on a 3-port diffraction grating. We show
that power-recycling of a high-finesse arm cavity is possible without
transmitting any laser power through a substrate material. The power splitting
ratio of the three output ports of the grating is, surprisingly, noncritical
Michelson interferometer with diffractively-coupled arm resonators in second-order Littrow configuration
Michelson-type laser-interferometric gravitational-wave (GW) observatories
employ very high light powers as well as transmissively- coupled Fabry-Perot
arm resonators in order to realize high measurement sensitivities. Due to the
absorption in the transmissive optics, high powers lead to thermal lensing and
hence to thermal distortions of the laser beam profile, which sets a limit on
the maximal light power employable in GW observatories. Here, we propose and
realize a Michelson-type laser interferometer with arm resonators whose
coupling components are all-reflective second-order Littrow gratings. In
principle such gratings allow high finesse values of the resonators but avoid
bulk transmission of the laser light and thus the corresponding thermal beam
distortion. The gratings used have three diffraction orders, which leads to the
creation of a second signal port. We theoretically analyze the signal response
of the proposed topology and show that it is equivalent to a conventional
Michelson-type interferometer. In our proof-of-principle experiment we
generated phase-modulation signals inside the arm resonators and detected them
simultaneously at the two signal ports. The sum signal was shown to be
equivalent to a single-output-port Michelson interferometer with
transmissively-coupled arm cavities, taking into account optical loss. The
proposed and demonstrated topology is a possible approach for future
all-reflective GW observatory designs
Monolithic dielectric surfaces as new low-loss light-matter interfaces
We propose a new mirror architecture, which is solely based upon structuring of the surface of a monolithic, possibly monocrystalline, bulk material. We found that a structure of T-shaped ridges of a subwavelength grating can theoretically provide 100% reflectivity. Since no material needs to be added to the mirror device, lowest mechanical loss can also be expected. Our approach might have compelling applications as a new light-matter interface
100% reflectivity from a monolithic dielectric microstructured surface
Here, we propose a new mirror architecture which is solely based upon a monolithic dielectric micro-structured surface. Hence, the mirror device, which consists of a possibly mono-crystalline bulk material, can in principle simultaneously provide perfect reflectivity and lowest mechanical loss. By specifically structuring the monolithic surface, resulting in T-shaped ridges of a subwavelength grating, a resonant behavior of light coupling can be realized, leading to theoretically 100% reflectivity
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