University of Birmingham > Talks@bham > Astrophysics Seminars > Fabrication of Ta2O5, Zr:Ta2O5 and aSi by ECR ion beam deposition for use as high-index coating layers in ultra-stable optical cavities with low Brownian thermal noise.

Fabrication of Ta2O5, Zr:Ta2O5 and aSi by ECR ion beam deposition for use as high-index coating layers in ultra-stable optical cavities with low Brownian thermal noise.

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If you have a question about this talk, please contact Dr Matteo Bianconi.

Precision metrology applications, such as mHz-linewidth laser cavities for optical clocks and stabilized frequency combs, and fundamental physics experiments such as gravitational wave detectors, impose stringent requirements on optical and mechanical losses in the multilayer HR mirror coatings. In the case of current and future gravitational wave detectors, only ion beam deposition (IBD) has been demonstrated to satisfy the optical requirements over suitably large areas (mirror diameter ³ 340 mm). Advanced gravitational wave detectors currently use mirror coatings fabricated from multilayers of silica (SiO2, low index) and alloys of tantalum pentoxide and titanium dioxide (Ti:Ta2O5, high index). Coating Brownian thermal noise, which predominantly arises from the high index materials, sets an important limit on the astrophysical reach of all current and future detectors. Developing materials and methods by which the thermal noise can be reduced by a factor of 2, whilst maintaining the required optical properties, is a goal for the various international projects in this field. This presentation will provide an overview of the first use of electron cyclotron resonance (ECR) IBD processes for the fabrication of optical thin film coatings, with unprecedented levels of optical and mechanical losses. ECR ion sources provide a number of key benefits compared to standard RF ion sources, through extending the accessible ion energies by an order of magnitude, and in the removal of grids (contamination) in the plasma extraction process. Amorphous silicon fabricated by ECR -IBD has been demonstrated to have optical absorptions down to k = 1.2 × 10−5 at 1550 nm, the lowest ever reported, and with potential to reach the thermal noise requirements at this wavelength. Recent results on alloys of tantalum pentoxide and zirconium dioxide are presented, which shows partial progress towards the same goal whilst enabling the laser wavelength in the optical cavities to remain at 1064 nm.

This talk is part of the Astrophysics Seminars series.

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