Measurement and reduction of laser power fluctuations beyond the shot noise limit

authored by: Jasper Robert Venneberg
supervised by: Benno Willke
Abstract: Many experiments in state-of-the-art research rely on highly stable light sources. For example, gravitational-wave detectors demand ultra-low-noise lasers to meet their stringent sensitivity requirements. In particular, exceptionally low laser power noise is necessary. Classically, laser power noise measurements are restricted by shot noise. Shot-noise-limited sensing can be improved conventionally by increasing the detected power. However, the power handling capabilities of photodetectors impose constraints on this approach, limiting current-day power noise monitoring and reduction techniques. This work investigates methods to surpass the limit imposed by shot noise. Concepts usable in both low- and high-power setups are examined, which could improve the sensitivity of future high-precision experiments in metrology and spectroscopy. A power noise monitoring method is demonstrated, capable of sub-shot-noise measurements by correlating the signals of two photodetectors. Without the need of a complex optical setup, this technique, called quantum correlation measurement, is demonstrated to achieve a relative power noise sensitivity one order of magnitude below what is achievable via a conventional shot-noise-limited measurement. This technique could increase sensitivity and considerably reduce technical effort in power noise monitoring. A nonclassical power stabilization scheme is demonstrated, which enables power stability beyond the classical limit of active stabilization. A bright squeezed output beam with a power of up to 9.9 mW and sub-shot-noise power fluctuations for frequencies from 550 Hz to 70 kHz at levels of up to 5.7 +0.3/-0.4 dB below shot noise is generated. As an effective bright squeezed light source, this method could enable future high-precision measurements in low-power applications otherwise limited by shot noise. Finally, concepts for future bright squeezing schemes are investigated. Bright squeezed light generation via passive power noise filtering by a cavity and active stabilization based on optical AC coupling are examined. Case studies for proof-of-principle experiments are performed, and the feasibility is shown by applying realistic parameters. The scalability of the optical AC coupling assisted bright squeezing technique to powers of hundreds of watts is illustrated by applying parameters for a future gravitational-wave detector.
Organisation(s): Institute of Gravitation Physics
QUEST-Leibniz Research School
Type: Doctoral thesis
No. of pages: 125
Publication date: 2024
Publication status: Published
Electronic version(s): https://doi.org/10.15488/17858 (Access: Open)
: Details in the research portal "Research@Leibniz University"

BibTeX

@phdthesis{64248a3982804d4ba00bb92de6db2cb0,
title = "Measurement and reduction of laser power fluctuations beyond the shot noise limit",
abstract = "Many experiments in state-of-the-art research rely on highly stable light sources. For example, gravitational-wave detectors demand ultra-low-noise lasers to meet their stringent sensitivity requirements. In particular, exceptionally low laser power noise is necessary. Classically, laser power noise measurements are restricted by shot noise. Shot-noise-limited sensing can be improved conventionally by increasing the detected power. However, the power handling capabilities of photodetectors impose constraints on this approach, limiting current-day power noise monitoring and reduction techniques. This work investigates methods to surpass the limit imposed by shot noise. Concepts usable in both low- and high-power setups are examined, which could improve the sensitivity of future high-precision experiments in metrology and spectroscopy. A power noise monitoring method is demonstrated, capable of sub-shot-noise measurements by correlating the signals of two photodetectors. Without the need of a complex optical setup, this technique, called quantum correlation measurement, is demonstrated to achieve a relative power noise sensitivity one order of magnitude below what is achievable via a conventional shot-noise-limited measurement. This technique could increase sensitivity and considerably reduce technical effort in power noise monitoring. A nonclassical power stabilization scheme is demonstrated, which enables power stability beyond the classical limit of active stabilization. A bright squeezed output beam with a power of up to 9.9 mW and sub-shot-noise power fluctuations for frequencies from 550 Hz to 70 kHz at levels of up to 5.7 +0.3/-0.4 dB below shot noise is generated. As an effective bright squeezed light source, this method could enable future high-precision measurements in low-power applications otherwise limited by shot noise. Finally, concepts for future bright squeezing schemes are investigated. Bright squeezed light generation via passive power noise filtering by a cavity and active stabilization based on optical AC coupling are examined. Case studies for proof-of-principle experiments are performed, and the feasibility is shown by applying realistic parameters. The scalability of the optical AC coupling assisted bright squeezing technique to powers of hundreds of watts is illustrated by applying parameters for a future gravitational-wave detector.",
author = "Venneberg, {Jasper Robert}",
year = "2024",
doi = "10.15488/17858",
language = "English",
publisher = "Leibniz Universit{\"a}t Hannover",
school = "Leibniz University Hannover",
}