Regensburg 2025 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 29: Poster II

HL 29.49: Poster

Dienstag, 18. März 2025, 18:00–20:00, P1

Birefringence effects in crystalline AlGaAs/GaAs mirror coatings from 4 K to room temperature — •Mona Kempkes, Chun Yu Ma, Thomas Legero, Uwe Sterr, and Daniele Nicolodi — Physikalisch-Technische Bundesanstalt, Braunschweig

Coating thermal noise limits the performance of high precision interferometry experiments, including ultra-stable optical oscillators used for interrogating atomic clocks and gravitational wave detectors. Due to their low mechanical losses, Bragg-reflectors from crystalline Al_0.92Ga_0.08As/GaAs heterostructures emerged as a lower thermal noise alternative to traditional dielectric mirror coatings. Mirrors realized with this material exhibit still poorly understood birefringence that can be modified by temperature and incident optical power. Furthermore, experiments at 4 K, 16 K and 124 K revealed spontaneous fluctuations of the birefringence, as well as an additional and yet unidentified noise source that limits the performance well above the expected thermal noise floor [J. Yu et al., Phys. Rev. X 13, 041002 (2023)]. Reconciling these observations from different samples is challenging and hinders a common interpretation. Thus we have set up one system where the temperature can be swept continuously across a wide range. We will present our setup based on a low-vibration closed-cycle cryostat, and measurements of the birefringence of crystalline AlGaAs/GaAs mirror coatings from 4 K to room temperature and as function of optical power.

Keywords: AlGaAs/GaAs; Heterostructures; Birefringence; Cryogenics