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THU: Thursday Contributed Sessions

THU 13: Poster Session: Applications

THU 13.79: Poster

Thursday, September 11, 2025, 16:30–18:30, ZHG Foyer 1. OG

Observation of squeezed light in the 2-um range in the signal band of future gravitational wave observatories — Julian Gurs, •Nils Sültmann, and Roman Schnabel — University of Hamburg, Hamburg, Germany

Next generation of squeezed-light-enhanced gravitational wave (GW) observatories could achieve higher sensitivities by reducing the thermal noise of the suspended mirrors, which involves shifting the wavelength into the 2-um range [1,2]. Photodiodes made of extended InGaAs are available for this wavelength regime, but their quantum efficiencies in the low frequency signal band of GW observatories is strongly limited by photo diode dark noise [3,4]. Here we present the successful extension of 2128-nm-squeezed-light measurements [4] into the signal band of a few ten hertz of typical GWs.

The squeeze factor achieved is limited by the photodiode*s quantum efficiency. Our results show that photodiodes with higher quantum efficiency must be developed for wavelengths in the 2*m range so that squeeze factors of *10dB become possible.
[1] A cryogenic silicon interferometer for gravitational-wave detection by R. X. Adhikari (10.1088/1361-6382/ab9143)
[2] Silicon-Based Optical Mirror Coatings for Ultrahigh Precision Metrology and Sensing by J. Steinlechner (10.1103/PhysRevLett.120.263602)
[3] Squeezed vacuum phase control at 2 µm by M. J. Yap (10.1364/OL.44.005386)

Keywords: Photodiodes; Quantum-efficency; squeezed light; 2128 nm