Optical absorption measurements on crystalline silicon test masses at 1550 nm

Steinlechner, J.; Krüger, Christoph; Lastzka, N.; Steinlechner, S.; Khalaidovski, A.; Schnabel, R.

doi:10.1088/0264-9381/30/9/095007

Cited by 7 publications

(16 citation statements)

References 22 publications

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“…Both results are in good mutual agreement. Our absorption coefficient of α si (1550nm) ≈ 40 /cm found for the ion plated silicon layers of our coating stack is lower than values of 100 /cm up to 2000 /cm reported for a-Si [12][13][14], while for c-Si the absorption coefficient is only in the order of a few ppm/cm up to a few hundreds ppm/cm at 1550 nm [10,22,26]. Our result reveals a rather modest reduction of optical absorption for Si layers deposited by ion plating instead of the ion beam sputtering technique, and the coating investigated has an absorption that is still far too high for test mass mirrors in GWDs.…”

Section: Discussioncontrasting

confidence: 69%

Optical absorption measurement at 1550 nm on a highly-reflective Si/SiO ₂ coating stack

Steinlechner

Khalaidovski

Schnabel

2014

Class. Quantum Grav.

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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 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 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• 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 nm and for an angle of incidence of 44• . We used the photothermal self-phase modulation technique to measure the coating absorption in s-polarization and p-polarization. We obtained α coat s = (1035 ± 42) ppm and α coat p = (1428 ± 97) ppm. These results correspond to an absorption coefficient which is lower than literature values for a-Si which vary from 100 cm −1 up to 2000 cm −1 . 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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Section: Discussioncontrasting

confidence: 69%

Optical absorption measurement at 1550 nm on a highly-reflective Si/SiO ₂ coating stack

Steinlechner

Khalaidovski

Schnabel

2014

Class. Quantum Grav.

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“…At low intensities no non-linear contribution to the free-carrier absorption takes place. As outlined in [8], from the residual doping of the crystal an absorption coefficient of α ≈ 1 ppm/cm can be predicted, excluding this effect as a possible explanation for the observed high absorption values. The expected contribution is shown in trace (b) of Fig.…”

Section: Discussionmentioning

confidence: 87%

“…Both the bulk absorption and the absorption in the surfaces beneath the HR Free-carrier absorption calculated for the residual doping in our sample (p-doping, N = 2 × 10 12 /cm 3 ) using the theory presented in [16]. (c, red circle) Total optical absorption in a prototype crystalline silicon test mass measured at an intensity of 2.2 kW/cm 2 and scaled to the cavity round-trip length [8]. (d, head-down blue triangle) Bulk absorption of a silicon crystal measured with a beam deflection approach at an intensity of 2.2 kW/cm 2 [9].…”

Section: Discussionmentioning

confidence: 99%

“…While predictions basing on photocurrent measurements led to the hope for subppm/cm absorption at 1550 nm [6,7], to the best of our knowledge only recently first direct sensitive measurements of the optical absorption of undoped samples at 1550 nm were presented [8,9]. In [8] we have reported an optical absorption of α = 264 ppm/cm. This value is two orders of magnitude higher than expected from the residual doping of the silicon crystal (the specific resistivity was specified to 11 kΩcm).…”

Section: Introductionmentioning

confidence: 99%

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

Khalaidovski

Steinlechner

Schnabel

2013

Class. Quantum Grav.

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The sensitivity of future gravitational wave (GW) observatories will be limited by thermal noise in a wide frequency band. To reduce thermal noise, the European GW observatory Einstein GW Telescope (ET) is suggested to use crystalline silicon test masses at cryogenic temperature and a laser wavelength of 1550 nm. Here, we report a measurement of the optical loss in a prototype high-resistivity crystalline silicon test mass as a function of optical intensity at room temperature. The total loss from both the bulk crystal and the surfaces was determined in a joint measurement. The characterization window ranged from small intensities below 1 W/cm 2 , as planned to be used in ET, up to 21 kW/cm 2 . A non-linear absorption was observed for intensities above a few kW/cm 2 . In addition we have observed an intensity-independent offset that possibly arises from absorption in the crystal surfaces. This absorption was estimated to α surf ≈ 800 ppm/surface, which might be too high for a cryogenic operation of a fibre-suspended silicon test mass. Such an offset was not observed in other recent measurements that were insensitive to surface absorption. Finally, a set of further characterization measurements is proposed to clearly separate the contributions from the surfaces and the bulk crystal. arXiv:1304.4126v1 [physics.optics]

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“…For practical devices, further reduction of the pump power is key, especially when it comes to integrated Kerr comb modules in which the available pump power is limited [52][53][54][55]. In this context, improvements in waveguide fabrication may allow reducing the linear propagation losses to values of, e.g., 0.4 dB cm −1 [56], which is well below the 2 dB cm −1 assumed in this work, but still far above the intrinsic absorption of silicon of less than 0.01 dB cm −1 at telecommunication wavelengths [57]. As an alternative or an addition to reversebiased p-i-n junctions, silicon self ion implantation may be used to reduce of the FC dwell time at the expense of slightly increased waveguide losses [58].…”

Section: Discussionmentioning

confidence: 74%

Analysis of Kerr comb generation in silicon microresonators under the influence of two-photon absorption and fast free-carrier dynamics

et al. 2021

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Kerr frequency comb generation relies on dedicated waveguide platforms that are optimized toward ultralow loss while offering comparatively limited functionality restricted to passive building blocks. In contrast to that, the silicon-photonic platform offers a highly developed portfolio of high-performance devices, but suffers from strong two-photon absorption (TPA) and subsequent free-carrier absorption (FCA) at near-infrared telecommunication wavelengths, thereby rendering Kerr comb generation a challenge. Here we present a model to investigate the impact of TPA and FCA on Kerr comb formation. Our model combines a modified version of the Lugiato-Lefever equation with a refined relation to precisely describe the fast space and time dependence of the free-carrier concentration along the circumference of the microresonator. Using this refined model, we derive conditions for modulation instability, in particular for necessary pump powers depending on TPA parameters and free-carrier lifetimes. We validate our analytical predictions by time integration and study the impact of fast free-carrier dynamics on Kerr comb formation. We find that silicon microresonators may be suitable for Kerr comb generation in the NIR, provided that the dwell time of the TPA-generated free carriers in the waveguide core is reduced by a reverse-biased p-i-n-junction and that the pump parameters are chosen appropriately.

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Optical absorption measurements on crystalline silicon test masses at 1550 nm

Cited by 7 publications

References 22 publications

Optical absorption measurement at 1550 nm on a highly-reflective Si/SiO ₂ coating stack

Optical absorption measurement at 1550 nm on a highly-reflective Si/SiO ₂ coating stack

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

Analysis of Kerr comb generation in silicon microresonators under the influence of two-photon absorption and fast free-carrier dynamics

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Optical absorption measurements on crystalline silicon test masses at 1550 nm

Cited by 7 publications

References 22 publications

Optical absorption measurement at 1550 nm on a highly-reflective Si/SiO 2 coating stack

Optical absorption measurement at 1550 nm on a highly-reflective Si/SiO 2 coating stack

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

Analysis of Kerr comb generation in silicon microresonators under the influence of two-photon absorption and fast free-carrier dynamics

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Optical absorption measurement at 1550 nm on a highly-reflective Si/SiO ₂ coating stack

Optical absorption measurement at 1550 nm on a highly-reflective Si/SiO ₂ coating stack