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Applied Optics

Applied Optics


  • Editor: Joseph N. Mait
  • Vol. 53, Iss. 7 — Mar. 1, 2014
  • pp: 1315–1321

Low scatter and ultra-low reflectivity measured in a fused silica window

Cinthia Padilla, Peter Fritschel, Fabian Magaña-Sandoval, Erik Muniz, Joshua R. Smith, and Liyuan Zhang  »View Author Affiliations

Applied Optics, Vol. 53, Issue 7, pp. 1315-1321 (2014)

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We investigate the reflectivity and optical scattering characteristics at 1064 nm of an antireflection coated fused silica window of the type being used in the Advanced LIGO gravitational-wave detectors. Reflectivity is measured in the ultra-low range of 5–10 ppm (by vendor) and 14–30 ppm (by us). Using an angle-resolved scatterometer we measure the sample’s bidirectional scattering distribution function (BSDF) and use this to estimate its transmitted and reflected scatter at roughly 20–40 and 1 ppm, respectively, over the range of angles measured. We further inspect the sample’s low backscatter using an imaging scatterometer, measuring an angle resolved BSDF below 10 6 sr 1 for large angles (10°–80° from incidence in the plane of the beam). We use the associated images to (partially) isolate scatter from different regions of the sample and find that scattering from the bulk fused silica is on par with backscatter from the antireflection coated optical surfaces. To confirm that the bulk scattering is caused by Rayleigh scattering, we perform a separate experiment measuring the scattering intensity versus input polarization angle. We estimate that 0.9–1.3 ppm of the backscatter can be accounted for by Rayleigh scattering of the bulk fused silica. These results indicate that modern antireflection coatings have low enough scatter to not limit the total backscattering of thick fused silica optics.

© 2014 Optical Society of America

OCIS Codes
(110.0110) Imaging systems : Imaging systems
(120.5820) Instrumentation, measurement, and metrology : Scattering measurements
(310.1210) Thin films : Antireflection coatings
(290.1483) Scattering : BSDF, BRDF, and BTDF

ToC Category:

Original Manuscript: December 5, 2013
Manuscript Accepted: January 8, 2014
Published: February 24, 2014

Virtual Issues
May 22, 2014 Spotlight on Optics

Cinthia Padilla, Peter Fritschel, Fabian Magaña-Sandoval, Erik Muniz, Joshua R. Smith, and Liyuan Zhang, "Low scatter and ultra-low reflectivity measured in a fused silica window," Appl. Opt. 53, 1315-1321 (2014)

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