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Dr. Benjamin Knispel
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Henning Vahlbruch, Dennis Wilken, Moritz Mehmet, and Benno Willke
Laser Power Stabilization beyond the Shot Noise Limit Using Squeezed Light
DOI

More stable laser light with squeezing

AEI researchers show how to improve laser power stability by the injection of a squeezed vacuum

October 22, 2018

AEI researchers have demonstrated how to improve high precision metrology applications that use high laser power. They demonstrated a nonclassical way to improve the achievable power stability without increasing the detected power. By the injection of a squeezed vacuum field of light they improved the classical laser power stability beyond its shot noise limit.
Noise budget of the squeezing enhanced laser power stabilization. (a) Measured out-of-loop laser noise normalized to the shot noise level of the 90.6 uA in-loop detected power. (b) In-loop measurement of the free-running laser power noise suppressed by the electronic loop gain. (c) Electronic dark noise of the in-loop photodetector. (d) Nonclassical laser power noise reduction. Between 5–80 kHz an average of 9.4+0.6−0.6 dB below the shot noise was achieved. (e) Simulated squeezing enhancement. (f) Uncorrelated sum of limiting noise sources (b),(c),(e). Zoom Image
Noise budget of the squeezing enhanced laser power stabilization. (a) Measured out-of-loop laser noise normalized to the shot noise level of the 90.6 uA in-loop detected power. (b) In-loop measurement of the free-running laser power noise suppressed by the electronic loop gain. (c) Electronic dark noise of the in-loop photodetector. (d) Nonclassical laser power noise reduction. Between 5–80 kHz an average of 9.4+0.6−0.6 dB below the shot noise was achieved. (e) Simulated squeezing enhancement. (f) Uncorrelated sum of limiting noise sources (b),(c),(e). [less]

Paper abstract 

High levels of laser power stability are necessary for high precision metrology applications. The classical limit for the achievable power stability is determined by the shot noise of the light used to generate a power control signal. Increasing the power of the detected light reduces the relative shot noise level and allows higher stabilities. However, sufficiently high power is not always available and the detection of high laser powers is challenging. Here, we demonstrate a nonclassical way to improve the achievable power stability without increasing the detected power. By the injection of a squeezed vacuum field of light we improve the classical laser power stability beyond its shot noise limit by 9.4+0.6−0.6  dB at Fourier frequencies between 5 and 80 kHz. For only 90.6  μA of detected photocurrent we achieve a relative laser power noise of 2.0+0.1−0.1×10−8/√Hz. This is the first demonstration of a squeezed light-enhanced laser power stabilization and its performance is equivalent to an almost tenfold increase of detected laser power in a classical scheme. The analysis reveals that the technique presented here has the potential to achieve stability levels of 4.2×10−10/√Hz with 58 mA photocurrent measured on a single photodetector.

 
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