Abstract
We demonstrate a method to measure and actively reduce the coupling of vibrations to the phase noise of a cavity-stabilized laser. This method uses the vibration noise of the laboratory environment rather than active drive to perturb the optical cavity. The laser phase noise is measured via a beat note with a second unperturbed ultra-stable laser while the vibrations are measured by accelerometers positioned around the cavity. A Wiener filter algorithm extracts the frequency and direction dependence of the cavity response function. Once the cavity response function is known, real-time noise cancellation can be implemented by use of the accelerometer measurements to predict and then cancel the laser phase fluctuations. We present real-time noise cancellation that results in a 25 dB reduction of the laser phase noise power spectral density.
Highlights
Lasers locked to well isolated Fabry-Perot cavities provide the highest short-term fractionalfrequency stability [1]
For high-finesse cavities, the large signal-to-noise ratio (SNR) of the Pound-Drever-Hall (PDH) stabilization technique [2] allows laser frequencies to track the cavity resonance with negligible added noise. In this situation the laser’s frequency stability is determined primarily by the length stability of the cavity. This length stability is limited fundamentally by intrinsic thermomechanical noise [1,3,4], but the thermomechanical noise can be exceeded by vibration-induced length changes
Such frequency-stable lasers play a crucial role in a wide range of scientific investigations including: optical atomic clocks [5], gravitational wave detectors [6], and searches for the time variation of fundamental constants [7], but their use is currently confined to quiet laboratory settings
Summary
Lasers locked to well isolated Fabry-Perot cavities provide the highest short-term fractionalfrequency stability [1]. For high-finesse cavities, the large signal-to-noise ratio (SNR) of the Pound-Drever-Hall (PDH) stabilization technique [2] allows laser frequencies to track the cavity resonance with negligible added noise. In this situation the laser’s frequency stability is determined primarily by the length stability of the cavity. In this work we discuss the application of Wiener filters [13] to measure the vibration sensitivity of a laser stabilization cavity, and to reduce this sensitivity with real-time corrections This technique yields information about the cavity’s vibration response function, which can be used to improve the mechanical design and minimize the residual vibration sensitivity. The cavity response function is used to calculate real-time corrections to the laser frequency from measured accelerations and demonstrate a vibration-sensitivity reduction
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