5,466 research outputs found
Three-port beam splitters-combiners for interferometer applications
We derive generic phase and amplitude coupling relations for beam
splitters-combiners that couple a single port with three output ports or input
ports, respectively. We apply the coupling relations to a reflection grating
that serves as a coupler to a single-ended Fabry-Perot ring cavity. In the
impedance-matched case such an interferometer can act as an all-reflective ring
mode cleaner. It is further shown that in the highly undercoupled case almost
complete separation of carrier power and phase signal from a cavity strain can
be achieved
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
Demonstration of 3-port grating phase relations
We experimentally demonstrate the phase relations of 3-port gratings by
investigating 3-port coupled Fabry-Perot cavities. Two different gratings which
have the same 1st order diffraction efficiency but differ substantially in
their 2nd order diffraction efficiency have been designed and manufactured.
Using the gratings as couplers to Fabry-Perot cavities we could validate the
results of an earlier theoretical description of the phases at a three port
grating
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
Input-output relations for a 3-port grating coupled Fabry-Perot cavity
We analyze an optical 3-port reflection grating by means of a scattering
matrix formalism. Amplitude and phase relations between the 3 ports, i.e. the 3
orders of diffraction are derived. Such a grating can be used as an
all-reflective, low-loss coupler to Fabry-Perot cavities. We derive the input
output relations of a 3-port grating coupled cavity and find distinct
properties not present in 2-port coupled cavities. The cavity relations further
reveal that the 3-port coupler can be designed such that the additional cavity
port interferes destructively. In this case the all-reflective, low-loss,
single-ended Fabry-Perot cavity becomes equivalent to a standard transmissive,
2-port coupled cavity
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
The Little Engine That Could – How to Start the Motor? Motivating the Online Student
Motivation is a function of initiating and sustaining goal-directed action. In addition to individual variables, student motivation is influenced by situational variables that include course design, instructional approach, and to a great extent, faculty behavior. This article presents classic literature on motivation and offers a grounded set of instructional methods and strategies with which faculty can spark and sustain motivation that leads to deep rather than superficial learning in the online learner. These classic motivational techniques have a direct relationship with today's online learner. The authors highlight the significance of external influences and describe some of the many opportunities available to faculty to enhance the motivation of online students to learn
Diffractive Optics for Gravitational Wave Detectors
All-reflective interferometry based on nano-structured diffraction gratings
offers new possibilities for gravitational wave detection. We investigate an
all-reflective Fabry-Perot interferometer concept in 2nd order Littrow mount.
The input-output relations for such a resonator are derived treating the
grating coupler by means of a scattering matrix formalism. A low loss
dielectric reflection grating has been designed and manufactured to test the
properties of such a grating cavity
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
Small cisterno-lumbar gradient of phosphorylated Tau protein in geriatric patients with suspected normal pressure hydrocephalus
Additional file 1. Dementia markers Spinal tap fraction 1 and 8
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