Waveguide grating mirror in a fully suspended 10 meter Fabry-Perot cavity

• Published in: Optics express Vol. 19; no. 16; pp. 14955 - 14963
• Main Authors: Friedrich, Daniel, Barr, Bryan W, Brückner, Frank, Hild, Stefan, Nelson, John, Macarthur, John, Plissi, Michael V, Edgar, Matthew P, Huttner, Sabina H, Sorazu, Borja, Kroker, Stefanie, Britzger, Michael, Kley, Ernst-Bernhard, Danzmann, Karsten, Tünnermann, Andreas, Strain, Ken A, Schnabel, Roman
• Format: Journal Article
• Language: English
• Published: United States 01-08-2011
• ISSN: 1094-4087; 1094-4087
• DOI: 10.1364/OE.19.014955

We report on the first demonstration of a fully suspended 10 m Fabry-Perot cavity incorporating a waveguide grating as the coupling mirror. The cavity was kept on resonance by reading out the length fluctuations via the Pound-Drever-Hall method and employing feedback to the laser frequency. From the achieved finesse of 790 the grating reflectivity was determined to exceed 99.2% at the laser wavelength of 1064 nm, which is in good agreement with rigorous simulations. Our waveguide grating design was based on tantala and fused silica and included a ≈ 20 nm thin etch stop layer made of Al2O3 that allowed us to define the grating depth accurately and preserve the waveguide thickness during the fabrication process. Demonstrating stable operation of a waveguide grating featuring high reflectivity in a suspended low-noise cavity, our work paves the way for the potential application of waveguide gratings as mirrors in high-precision interferometry, for instance in future gravitational wave observatories.