Low-loss mirrors fabricated by ion-beam-sputtering machines for possible application in an interferometric gravitational wave antenna were evaluated by use of Nd:YAG laser light (λ = 1064 nm) with two distinct measurements: a tabletop experiment that used a short cavity with a small beam with a beam waist of approximately 2<i>w</i><sub>0</sub> = 0.82 mm, and an optical test that used a 20-m prototypical gravitational-wave detector with a large beam with a beam waist of approximately 2<i>w</i><sub>0</sub> = 4.4 mm. A multilayer coating comprised 29 layers of SiO<sub>2</sub>/Ta<sub>2</sub>O<sub>5</sub> and one protective coating of SiO<sub>2</sub>. The best values obtained as a result of these measurements were 16 ppm (parts in 10<sup>6</sup>) and 30 ppm in total loss, respectively. Also, a two-dimensional loss map generated by use of a small beam successfully revealed the existence of a loss structure within the coating surface. These results imply that a high-reflectance multilayer coating has some inhomogeneities and a loss distribution with a typical scale of a few millimeters and that the total measured losses depend on the beam spot size.
© 1999 Optical Society of America
(230.4040) Optical devices : Mirrors
(230.4170) Optical devices : Multilayers
(240.0310) Optics at surfaces : Thin films
(290.5820) Scattering : Scattering measurements
(310.1620) Thin films : Interference coatings
Shuichi Sato, Shinji Miyoki, Masatake Ohashi, Masa-Katsu Fujimoto, Toshitaka Yamazaki, Mitsuhiro Fukushima, Akitoshi Ueda, Ken-ichi Ueda, Koji Watanabe, Kenji Nakamura, Kazuyuki Etoh, Naoya Kitajima, Kazuhiko Ito, and Izumi Kataoka, "Loss Factors of Mirrors for a gravitational wave Antenna," Appl. Opt. 38, 2880-2885 (1999)