Thermal noise reduction and absorption optimization via multimaterial coatings

Steinlechner, J., Martin, I. W. , Hough, J. , Krüger, C., Rowan, S. and Schnabel, R. (2015) Thermal noise reduction and absorption optimization via multimaterial coatings. Physical Review D, 91(4), 042001. (doi: 10.1103/PhysRevD.91.042001)

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Future gravitational wave detectors (GWDs) such as Advanced LIGO upgrades and the Einstein Telescope are planned to operate at cryogenic temperatures using crystalline silicon (cSi) test-mass mirrors at an operation wavelength of 1550 nm. The reduction in temperature in principle provides a direct reduction in coating thermal noise, but the presently used coating stacks which are composed of silica (SiO<sub>2</sub>) and tantala (Ta<sub>2</sub>O<sub>5</sub>) show cryogenic loss peaks which results in less thermal noise improvement than might be expected. Due to low mechanical loss at low temperature amorphous silicon (aSi) is a very promising candidate material for dielectric mirror coatings and could replace Ta<sub>2</sub>O<sub>5</sub>. Unfortunately, such an aSi/SiO<sub>2</sub> coating is not suitable for use in GWDs due to high optical absorption in aSi coatings. We explore the use of a three material based coating stack. In this multimaterial design the low absorbing Ta<sub>2</sub>O<sub>5</sub> in the outermost coating layers significantly reduces the incident light power, while aSi is used only in the lower bilayers to maintain low optical absorption. Such a coating design would enable a reduction of Brownian thermal noise by 25%. We show experimentally that an optical absorption of only (5.3±0.4)  ppm at 1550 nm should be achievable.

Item Type:Articles
Glasgow Author(s) Enlighten ID:Rowan, Professor Sheila and Martin, Dr Iain and Steinlechner, Dr Jessica and Hough, Professor James
Authors: Steinlechner, J., Martin, I. W., Hough, J., Krüger, C., Rowan, S., and Schnabel, R.
College/School:College of Science and Engineering > School of Physics and Astronomy
Research Centre:College of Science and Engineering > School of Physics and Astronomy > Institute for Gravitational Research
Journal Name:Physical Review D
Publisher:American Physical Society
ISSN (Online):1550-2368
Copyright Holders:Copyright © 2015 American Physical Society
First Published:First published in Physical Review D 91(4):042001
Publisher Policy:Reproduced in accordance with the copyright policy of the publisher.

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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
624341Investigations in Gravitational Radiation / Particle Astrophysics Capital equipmentSheila RowanScience & Technologies Facilities Council (STFC)ST/L000946/1S&E P&A - PHYSICS & ASTRONOMY