On the use of
Subwavelength Layered Titania-Silica
for Lowe thermal noise
Interferometer Coatings
Innocenzo M. Pinto
Maria Principe
Riccardo DeSalvo
University of Sannio at Benevento (IT), INFN and LVC
Comments on input parameters
• TiO2 losses assumed so far are inconsistent
and probably wrong (some likely belonging to
crystallized materials)
• The so far assumed Young’s modulus is wrong,
a value of 290 GPa (which is true for
crystalline form) is assumed while 190 GPa is
the measured value for the glassy form
TiO2 stability
• TiO2 layers crystalizes
• TiO2 stable for thin layers or for SiO2 dopant
– H. Sankur and G. Gunning, J. Appl. Phys. 66 (1989) 4747
• TiO2 stable when doped
W.H. Wang and S. Chao, Optics Lett., 23 (1998) 1417;
S. Chao, W.H. Wang, M.-Y. Hsu and L.-C. Wang, J. Opt. Soc. Am. A16 (1999) 1477;
S. Chao, W.H. Wang and C.C. Lee, Appl. Opt., 40 (2001) 2177;
SiO2 Coating Losses vs. Annealing T
• Annealing at high temperature is necessary to
keep mechanical losses low
Co-sputtered SiO2/TiO2::SiO2 CSIRO Tests
•
R.P. Netterfield and M. Gross, "Investigation of Ion Beam Sputtered Silica Titania
Mixtures for Use in GW Interferometer Optics," Optical Interference Coatings (OIC)
Conference, Tucson AZ, USA, 2007, paper Thd2
Claims: Annealing at 500C did not produce crystallization
A Direct Measurement of ø TiO2
• .
• What to do with all of this information?
• Example of stratified dychroic
coating:
• Using extreme values of
input parameters
• Obtain thermal noise levels
40% to 76% of what obtained
with doped Tantala in same
performance coating.
• Very promising prediction
Tests in process with Chao Shiu
20x