Optical absorption measurement at 1550 nm on a highly-reflective Si/SiO2 coating stack

Steinlechner, J., Khalaidovski, A. and Schnabel, R. (2014) Optical absorption measurement at 1550 nm on a highly-reflective Si/SiO2 coating stack. Classical and Quantum Gravity, 31(10), p. 105005. (doi: 10.1088/0264-9381/31/10/105005)

Abstract

Future laser-interferometric gravitational wave detectors (GWDs) will potentially employ test mass mirrors from crystalline silicon and a laser wavelength of 1550 nm, which corresponds to a photon energy belowthe silicon bandgap. Silicon might also be an attractive high-refractive index material for the dielectric mirror coatings. Films of amorphous silicon (a-Si), however, have been found to be significantly more absorptive at 1550 nm than crystalline silicon (c-Si).Here, we investigate the optical absorption of a Si/SiO2 dielectric coating produced with the ion plating technique. The ion plating technique is distinct from the standard state-of-the-art ion beam sputtering technique since it uses a higher processing temperature of about 250C, higher particle energies, and generally results in higher refractive indices of the deposited films. Our coating stack was fabricated for a reflectivity of R = 99.95% for s-polarized light at 1550 nm and for an angle of incidence of 44deg. We used the photothermal self-phase modulation technique to measure the coating absorption in s-polarization and p-polarization. We obtained αs = (1035 ± 42) ppm and αp = (1428±97) ppm. These results correspond to an absorption coefficient which is lower than literature values for a-Si which vary from 100/cm up to 2000/cm. It is, however, still orders of magnitude higher than expected for c-Si and thus still too high for GWD applications.

• Item Type: Articles
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Steinlechner, Dr Jessica
• Authors: Steinlechner, J., Khalaidovski, A., and Schnabel, R.
• Subjects: Q Science > QC Physics
• College/School: College of Science and Engineering > School of Physics and Astronomy
• Journal Name: Classical and Quantum Gravity
• Publisher: Institute of Physics
• ISSN: 0264-9381
• ISSN (Online): 1361-6382