906 research outputs found
Spatial and temporal filtering of a 10-W Nd:YAG laser with a Fabry-Perot ring-cavity premode cleaner
We report on the use of a fixed-spacer FabryâPerot ring cavity to filter spatially and temporally a 10-W laser-diode-pumped Nd:YAG master-oscillator power amplifier. The spatial filtering leads to a 7.6-W TEMinfinity beam with 0.1% higher-order transverse mode content. The temporal filtering reduces the relative power fluctuations at 10 MHz to 2.8 x 10^-/sqrtHz, which is 1 dB above the shot-noise limit for 50 mA of detected photocurrent
Charge neutralization in vacuum for non-conducting and isolated objects using directed low-energy electron and ion beams
We propose using ions and electrons of energy 1 eVâ10 eV for neutralizing the charges on the non-conducting or isolated surfaces of high-sensitivity experiments. The mirror surfaces of the test masses of the laser interferometer gravitational observatory are used as an example of the implementation of this method. By alternatively directing beams of positive and negative charges towards the mirror surfaces, we ensure the neutralization of the total charge as well as the equalization of the surface charge distribution to within a few eV of the potential of the ground reference of the vacuum system. This method is compatible with operation in high vacuum, does not require measuring the potential of the mirrors and is expected not to damage sensitive optical surfaces
Order within disorder: the atomic structure of ion-beam sputtered amorphous tantala (a-Ta2O5)
Amorphous tantala (a-Ta2O5) is a technologically important material often used in high-performance coatings. Understanding this material at the atomic level provides a way to further improve performance. This work details extended X-ray absorption fine structure measurements of a-Ta2O5 coatings, where high-quality experimental data and theoretical fits have allowed a detailed interpretation of the nearest-neighbor distributions. It was found that the tantalum atom is surrounded by four shells of atoms in sequence; oxygen, tantalum, oxygen, and tantalum. A discussion is also included on how these models can be interpreted within the context of published crystalline Ta 2O5 and other a-T2O5 studies
Investigating the medium range order in amorphous Ta<sub>2</sub>O<sub>5</sub> coatings
Ion-beam sputtered amorphous heavy metal oxides, such as Ta2O5, are widely used as the high refractive index layer of highly reflective dielectric coatings. Such coatings are used in the ground based Laser Interferometer Gravitational-wave Observatory (LIGO), in which mechanical loss, directly related to Brownian thermal noise, from the coatings forms an important limit to the sensitivity of the LIGO detector. It has previously been shown that heat-treatment and TiO2 doping of amorphous Ta2O5 coatings causes significant changes to the levels of mechanical loss measured and is thought to result from changes in the atomic structure. This work aims to find ways to reduce the levels of mechanical loss in the coatings by understanding the atomic structure properties that are responsible for it, and thus helping to increase the LIGO detector sensitivity. Using a combination of Reduced Density Functions (RDFs) from electron diffraction and Fluctuation Electron Microscopy (FEM), we probe the medium range order (in the 2-3 nm range) of these amorphous coatings
Elastic response of [111]-tunneling impurities
We study the dynamic response of a [111] quantum impurity, such as lithium or
cyanide in alkali halides, with respect to an external field coupling to the
elastic quadrupole moment. Because of the particular level structure of a
eight-state system on a cubic site, the elastic response function shows a
biexponential relaxation feature and a van Vleck type contribution with a
resonance frequency that is twice the tunnel frequency . This
basically differs from the dielectric response that does not show relaxation.
Moreover, we show that the elastic response of a [111] impurity cannot be
reduced to that of a two-level system. In the experimental part, we report on
recent sound velocity and internal friction measurements on KCl doped with
cyanide at various concentrations. At low doping (45 ppm) we find the dynamics
of a single [111] impurity, whereas at higher concentrations (4700 ppm) the
elastic response rather indicates strongly correlated defects. Our theoretical
model provides a good description of the temperature dependence of
and at low doping, in particular the relaxation peaks, the absolute
values of the amplitude, and the resonant contributions. From our fits we
obtain the value of the elastic deformation potential eV.Comment: 19 pages, 5 figure
GARIMAS 1 - GAlapagos RIft MAssive Sulphides : Cruise 32 of MS SONNE, 09.05.-09.07.1984 ; cruise report
Order within disorder: The atomic structure of ion-beam sputtered amorphous tantala (a-Ta_2O_5)
Amorphous tantala (a-Ta_2O_5) is a technologically important material often used in high-performance coatings. Understanding this material at the atomic level provides a way to further improve performance. This work details extended X-ray absorption fine structure measurements of a-Ta_2O_5 coatings, where high-quality experimental data and theoretical fits have allowed a detailed interpretation of the nearest-neighbor distributions. It was found that the tantalum atom is surrounded by four shells of atoms in sequence; oxygen, tantalum, oxygen, and tantalum. A discussion is also included on how these models can be interpreted within the context of published crystalline Ta 2O5 and other a-T_2O_5 studies
Spatial and temporal filtering of a 10-W Nd:YAG laser with a FabryâPerot ring-cavity premode cleaner
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