Indication for dominating surface absorption in crystalline silicon test masses at 1550 nm

Khalaidovski, A.; Steinlechner, J.; Schnabel, R.

doi:10.1088/0264-9381/30/16/165001

Cited by 13 publications

(17 citation statements)

References 20 publications

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“…Although this observation was not universal to all samples, it was common and was seen in samples from different vendors. It had also been reported elsewhere [13] that high purity samples might have significantly higher surface absorption than expected. This was something that had not been reported in similar studies of fused silica substrates undertaken in the visible or near infrared region.…”

Section: Motivationsupporting

confidence: 71%

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Anomalous optical surface absorption in nominally pure silicon samples at 1550 nm

Bell

Steinlechner

Martin

et al. 2017

Class. Quantum Grav.

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The announcement of the direct detection of gravitational waves (GW) by the LIGO and Virgo collaboration in February 2016 has removed any uncertainty around the possibility of GW astronomy. It has demonstrated that future detectors with sensitivities ten times greater than the Advanced LIGO detectors would see thousands of events per year. Many proposals for such future interferometric GW detectors assume the use of silicon test masses. Silicon has low mechanical loss at low temperatures, which leads to low displacement noise for a suspended interferometer mirror. In addition to the low mechanical loss, it is a requirement that the test masses have a low optical loss. Measurements at 1550 nm have indicated that material with a low enough bulk absorption is available; however there have been suggestions that this low absorption material has a surface absorption of >100 ppm which could preclude its use in future cryogenic detectors. We show in this paper that this surface loss is not intrinsic but is likely to be a result of particular polishing techniques and can be removed or avoided by the correct polishing procedure. This is an important step towards high gravitational wave detection rates in silicon based instruments.

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Section: Motivationsupporting

confidence: 71%

“…(1) amorphous silicon forming a layer or series of small islands on the surface due to mechanical effects during polishing [13]; (2) contamination due to material used during the polishing process becoming trapped within the surface.…”

Section: Silicon Etchmentioning

confidence: 99%

Anomalous optical surface absorption in nominally pure silicon samples at 1550 nm

Bell

Steinlechner

Martin

et al. 2017

Class. Quantum Grav.

Self Cite

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“…Optical absorption measurements done before on a monolithic cavity [14] reported a high surface absorption. Also, the calorimetric measurements will be extremely sensitive to such absorptions-either being caused by intrinsic surface effects or simply dirt on the surface.…”

Section: Investigation Of a Possible Surface Absorptionmentioning

confidence: 97%

“…As all absorption values reported in this paper are well above 100 ppm cm −1 any influence of the surface to our measurements can be excluded. Additionally, these results make the hypothesis of potential intrinsic strong surface absorptions in silicon very unlikely [14].…”

Section: Investigation Of a Possible Surface Absorptionmentioning

confidence: 98%

Measurement of the optical absorption of bulk silicon at cryogenic temperature and the implication for the Einstein Telescope

Degallaix

Komma

Forest

et al. 2014

Class. Quantum Grav.

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We report in this article on the measurement of the optical absorption of moderately doped crystalline silicon samples at 1550 nm, which is a candidate material for the main optics of the low temperature interferometer of the Einstein Telescope (ET). We observe a nearly constant absorption from room temperature down to cryogenic temperatures for two silicon samples presenting an optical absorption of 0.029 cm −1 and 780 ppm cm −1 , both crystals doped with boron. This is in contradiction to what was assumed previously-a negligible optical absorption at low temperature due to the carrier freezeout. As the main consequence, if the silicon intrinsic absorption can not be lowered, the cross section of the mirror suspension of the ET must be increased to be able to carry away the excess heat generated by the partially absorbed laser beam during the operation of the interferometer.

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“…24 The surface absorption is about ten times higher than the bulk value. The enhancement extracted from the distance dependent measurements is substantially less than reported in 16 which is particularly beneficial for applications in highprecision metrology where low noise is required. 5,6 The quadratic contribution to the silicon bulk deflection exceeds 5% at a pump beam intensity of about 2.3 × 10 5 W cm 2 ⁄ .…”

Section: Discussionmentioning

confidence: 83%

Key signal contributions in photothermal deflection spectroscopy

Dickmann

Bruns

et al. 2019

Journal of Applied Physics

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We report on key signal contributions in photothermal deflection spectroscopy (PDS) of semiconductors at photon energies below the bandgap energy and show how to extract the actual absorption properties from the measurement data. To this end, we establish a rigorous computation scheme for the deflection signal including semi-analytic raytracing to analyze the underlying physical effects. The computation takes into account linear and nonlinear absorption processes affecting the refractive index and thus leading to a deflection of the probe beam. We find that beside the linear mirage effect, nonlinear absorption mechanisms make a substantial contribution to the signal for strongly focussed pump beams and sample materials with high two-photon absorption coefficients. For example, the measured quadratic absorption contribution exceeds 5% at a pump beam intensity of about 1.3 × 10 5 W cm 2 ⁄ in Si and at 5 × 10 4 W cm 2 ⁄ in GaAs. In addition, our method also includes thermal expansion effects as well as spatial gradients of the attenuation properties. We demonstrate that these effects result in an additional deflection contribution which substantially depends on the distance of the photodetector from the readout point. This distance dependent contribution enhances the surface related PDS signal up to two orders of magnitude and may be misinterpreted as surface absorption if not corrected in the analysis of the measurement data. We verify these findings by PDS measurements on crystalline silicon at a wavelength of 1550 nm and provide guidelines how to extract the actual attenuation coefficient from the PDS signal.

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Indication for dominating surface absorption in crystalline silicon test masses at 1550 nm

Cited by 13 publications

References 20 publications

Anomalous optical surface absorption in nominally pure silicon samples at 1550 nm

Anomalous optical surface absorption in nominally pure silicon samples at 1550 nm

Measurement of the optical absorption of bulk silicon at cryogenic temperature and the implication for the Einstein Telescope

Key signal contributions in photothermal deflection spectroscopy

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