Microwave plasma assisted sputtering of a combined Ta2O5/SiO2 and a-Si:H/SiO2 two stack optical coating design concept for gravitational wave detectors

Connor Lindsay, Carlos García Nuñez, Lewis Fleming, Jonathan Pomfret, Kirstin Saunders, Sam Ahmadzadeh, Simon Tait, Stuart Reid, Iain Martin, Des Gibson

Research output: Chapter in Book/Report/Conference proceedingConference contribution

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Abstract

In this work, a new optical coating design concept is proposed for gravitational wave detector (GWD) utilising, microwave plasma assisted sputtering of a high reflector (HR) multi-material stack coating consisting of hydrogenated amorphous silicon (a-Si:H), Ta2O5 and SiO2 for GWD’s mirror coatings. This work includes the study of the optical, mechanical, structural and morphological properties of the coating to evaluate the potential of the materials for GWDs. Benefits of the microwave plasma assisted sputter deposition technique are described. a-Si is a promising alternative material for GWD mirror coatings, as it has been demonstrated to have reduced thermal noise, however, has optical absorption above the required level for GWDs. The HR multi-material coating design concept is a way potentially mediate the high absorption a-Si whilst taking advantage of its reduced thermal noise, incorporating the a-Si material into a Ta2O5 and SiO2 based HR multilayer coating. Hydrogenating a-Si (a-Si:H) is another method to reduce the absorption with the hydrogen concentration being an important parameter, this work combines these techniques to further lower the absorption. The multi-material coating consists of an ‘upper stack’ of Ta2O5/SiO2 low absorbing material on the incident side of the coating used to reflect the majority of the incident laser power and a ‘lower stack’ of a a-Si:H/SiO2 higher absorbing materials at the bottom of the coating where there is less laser power to be absorbed. In addition to investigating the effectiveness of the two-stack approach for optimum compromise between optical and mechanical loss reduction, this work also studies the effect of annealing on the properties of the multi-material coating. Moreover, effects of the deposition parameters such as deposition rate on each material are investigated and utilised to optimise properties the two-stack coating approach.
Original languageEnglish
Title of host publicationAdvances in Optical Thin Films VIII
EditorsMichel Lequime, Detlev Ristau
Place of PublicationBellingham
PublisherSociety of Photo-Optical Instrumentation Engineers
Volume13020
ISBN (Electronic)9781510673595
ISBN (Print)9781510673588
DOIs
Publication statusPublished - 24 Jun 2024
EventSPIE Phototonics Europe 2024 - Strasbourg, France
Duration: 7 Apr 202412 Apr 2024
https://www.spiedigitallibrary.org/conference-proceedings-of-SPIE/12999.toc#_=_

Publication series

NameSPIE Proceedings
PublisherSPIE
Volume13020
ISSN (Print)0277-786X
ISSN (Electronic)1996-756X

Conference

ConferenceSPIE Phototonics Europe 2024
Country/TerritoryFrance
CityStrasbourg
Period7/04/2412/04/24
Internet address

Keywords

  • gravitational wave detection
  • microwave plasma assisted sputtering
  • multi-material coating
  • hydrogenated amorphous silicon
  • coating thermal noise
  • optical absorption

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