719 research outputs found
Measurement of Birefringence of Low-Loss, High-Reflectance Coating of M-Axis Sapphire
The birefringence of a low-loss, high-reflectance coating applied to an 8-cm-diameter sapphire crystal grown in the m-axis direction has been mapped. By monitoring the transmission of a high-finesse Fabry-Perot cavity as a function of the polarization of the input light, we find an upper limit for the magnitude of the birefringence of 2.5 x 10^-4 rad and an upper limit in the variation in direction of the birefringence of 10 deg. These values are sufficiently small to allow consideration of m-axis sapphire as a substrate material for the optics of the advanced detector at the Laser Interferometer Gravitational Wave Observatory
Investigating the relationship between material properties and laser-induced damage threshold of dielectric optical coatings at 1064 nm
The Laser Induced Damage Threshold (LIDT) and material properties of various multi-layer amorphous dielectric
optical coatings, including Nb2O5, Ta2O5, SiO2, TiO2, ZrO2, AlN, SiN, LiF and ZnSe, have been studied. The coatings
were produced by ion assisted electron beam and thermal evaporation; and RF and DC magnetron sputtering at Helia
Photonics Ltd, Livingston, UK. The coatings were characterized by optical absorption measurements at 1064 nm by
Photothermal Common-path Interferometry (PCI). Surface roughness and damage pits were analyzed using atomic force
microscopy. LIDT measurements were carried out at 1064 nm, with a pulse duration of 9.6 ns and repetition rate of 100
Hz, in both 1000-on-1 and 1-on-1 regimes. The relationship between optical absorption, LIDT and post-deposition heattreatment
is discussed, along with analysis of the surface morphology of the LIDT damage sites showing both coating
and substrate failure
Medium range structural order in amorphous tantala spatially resolved with changes to atomic structure by thermal annealing
Amorphous tantala (a-Ta2O5) is an important technological material that has
wide ranging applications in electronics, optics and the biomedical industry.
It is used as the high refractive index layers in the multi-layer dielectric
mirror coatings in the latest generation of gravitational wave interferometers,
as well as other precision interferometers. One of the current limitations in
sensitivity of gravitational wave detectors is Brownian thermal noise that
arises from the tantala mirror coatings. Measurements have shown differences in
mechanical loss of the mirror coatings, which is directly related to Brownian
thermal noise, in response to thermal annealing. We utilise scanning electron
diffraction to perform Fluctuation Electron Microscopy (FEM) on Ion Beam
Sputtered (IBS) amorphous tantala coatings, definitively showing an increase in
the medium range order (MRO), as determined from the variance between the
diffraction patterns in the scan, due to thermal annealing at increasing
temperatures. Moreover, we employ Virtual Dark-Field Imaging (VDFi) to
spatially resolve the FEM signal, enabling investigation of the persistence of
the fragments responsible for the medium range order, as well as the extent of
the ordering over nm length scales, and show ordered patches larger than 5 nm
in the highest temperature annealed sample. These structural changes directly
correlate with the observed changes in mechanical loss.Comment: 22 pages, 5 figure
Optical absorption of ion-beam sputtered amorphous silicon coatings
Low mechanical loss at low temperatures and a high index of refraction should make silicon
optimally suited for thermal noise reduction in highly reflective mirror coatings for gravitational wave
detectors. However, due to high optical absorption, amorphous silicon (aSi) is unsuitable for being used
as a direct high-index coating material to replace tantala. A possible solution is a multimaterial design,
which enables exploitation of the excellent mechanical properties of aSi in the lower coating layers. The
possible number of aSi layers increases with absorption reduction. In this work, the optimum heat
treatment temperature of aSi deposited via ion-beam sputtering was investigated and found to be 450 °C.
For this temperature, the absorption after deposition of a single layer of aSi at 1064 nm and 1550 nm
was reduced by more than 80%
Nonlinear interaction between two heralded single photons
Harnessing nonlinearities strong enough to allow two single photons to
interact with one another is not only a fascinating challenge but is central to
numerous advanced applications in quantum information science. Currently, all
known approaches are extremely challenging although a few have led to
experimental realisations with attenuated classical laser light. This has
included cross-phase modulation with weak classical light in atomic ensembles
and optical fibres, converting incident laser light into a non-classical stream
of photon or Rydberg blockades as well as all-optical switches with attenuated
classical light in various atomic systems. Here we report the observation of a
nonlinear parametric interaction between two true single photons. Single
photons are initially generated by heralding one photon from each of two
independent spontaneous parametric downconversion sources. The two heralded
single photons are subsequently combined in a nonlinear waveguide where they
are converted into a single photon with a higher energy. Our approach
highlights the potential for quantum nonlinear optics with integrated devices,
and as the photons are at telecom wavelengths, it is well adapted to
applications in quantum communication.Comment: 4 pages, 4 figure
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