Loss factors of mirrors for a gravitational wave antenna.
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 (lambda = 1064 nm) with two distinct measurements: a tabletop experiment that used a short cavity with a small beam with a beam waist of approximately 2w(0) = 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 2w(0) = 4.4 mm. A multilayer coating comprised 29 layers of SiO(2)/Ta(2)O(5) and one protective coating of SiO(2). The best values obtained as a result of these measurements were 16 ppm (parts in 10(6)) 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.
Sato
S
S
Department of Astronomical Science, Graduate University for Advanced Studies, Mitaka, 181-8588 Tokyo, Japan. sato@gravity.mtk.nao.ac.jp
Miyoki
S
S
Ohashi
M
M
Fujimoto
M K
MK
Yamazaki
T
T
Fukushima
M
M
Ueda
A
A
Ueda
K
K
Watanabe
K
K
Nakamura
K
K
Etoh
K
K
Kitajima
N
N
Ito
K
K
Kataoka
I
I