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Optics Letters

Path length modulation technique for scatter noise immunity in squeezing measurements

Andrew R. Wade, S. Chua, Michael Stefszky, D. A. Shaddock, David E. McClelland

Published Jun 21, 2013• 4 citations
Publisher

Abstract

We present a technique for frequency shifting scattering induced noise on squeezed light beams, providing immunity from scattered light while preserving the squeezed states. Using a 500 Hz pre and postsqueezing apparatus path length modulation, we show up to a 20 dB reduction in scattering induced noise while recovering squeezing measurement below the shot noise level. Such a technique offers immunity to spurious scattering sources without the need for optically lossy isolation optics.

DOI
10.1364/ol.38.002265

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We present a technique for frequency shifting scattering induced noise on squeezed light beams, providing immunity from scattered light while preserving the squeezed states. Using a 500 Hz pre and postsqueezing apparatus path length modulation, we show up to a 20 dB reduction in scattering induced noise while recovering squeezing measurement below the shot noise level. Such a technique offers immunity to spurious scattering sources without the need for optically lossy isolation optics.
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In this article, we present a novel spectroscopy technique that improves the signal-to-shot-noise ratio without the need to increase the laser power. Detrimental effects by technical noise sources are avoided by frequency-modulation techniques (frequency up-shifting). Superimposing the signal on non-classical states of light leads to a reduced quantum noise floor. Our method reveals in a proof-of-concept experiment small signals at Hz to kHz frequencies even below the shot noise limit. Our theoretical calculations fully support our experimental findings. The proposed technique is interesting for applications such as high-precision cavity spectroscopy, e.g., for explosive trace gas detection where the specific gas might set an upper limit for the laser power employed.
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An improvement in precision beyond the limit set by the vacuum-state or zero-point fluctuations of the electromagnetic field is reported for the measurement of phase modulation in an optical interferometer. The experiment makes use of squeezed light to reduce the level of fluctuations below the shot-noise limit. An increase in the signal-to-noise ratio of 3.0 dB relative to the shot-noise limit is demonstrated, with the improvement currently limited by losses in propagation and detection and not by the degree of available squeezing.