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Optical Absorption Measurement at 1550 nm on a Highly-Reflective Si/SiO2 Coating Stack

Steinlechner, J., Khalaidovski, A., & Schnabel, R. (2014). Optical Absorption Measurement at 1550 nm on a Highly-Reflective Si/SiO2 Coating Stack. Classical and quantum gravity, 31(10): 105005. doi:10.1088/0264-9381/31/10/105005.

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Steinlechner, Jessica1, Author
Khalaidovski, Alexander1, Author
Schnabel, Roman1, Author
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1Laser Interferometry & Gravitational Wave Astronomy, AEI-Hannover, MPI for Gravitational Physics, Max Planck Society, ou_24010

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Free keywords: Physics, Optics, physics.optics
Abstract: Future laser-interferometric gravitational wave detectors (GWDs) will potentially employ test mass mirrors from crystalline silicon and a laser wavelength of $1550\,\rm{nm}$, which corresponds to a photon energy below the 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 $1550\,\rm{nm}$ than crystalline silicon (c-Si). Here, we investigate the optical absorption of a Si/SiO$_2$ 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 250$^\circ$C, 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 $1550\,\rm{nm}$ and for an angle of incidence of 44$^\circ$. We used the photothermal self-phase modulation technique to measure the coating absorption in s-polarization and p-polarization. We obtained $\alpha^{\rm coat}_{s}=(1035 \pm 42)\,\rm{ppm}$ and $\alpha^{\rm coat}_{p}=(1428 \pm 97)\,\rm{ppm}$. These results correspond to an absorption coefficient which is lower than literature values for a-Si which vary from $100\,\rm{/cm}$ up to $2000\,\rm{/cm}$. It is, however, still orders of magnitude higher than expected for c-Si and thus still too high for GWD applications.

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Dates: 2014-01-202014
Publication Status: Published in print
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Identifiers: arXiv: 1401.4916
DOI: 10.1088/0264-9381/31/10/105005
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### Source 1

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Title: Classical and quantum gravity
Source Genre: Journal
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Publ. Info: Bristol, U.K. : Institute of Physics
Pages: - Volume / Issue: 31 (10) Sequence Number: 105005 Start / End Page: - Identifier: ISSN: 0264-9381
CoNE: https://pure.mpg.de/cone/journals/resource/954925513480_1