Robust High-frequency Laser Phase Noise Suppression by Adaptive Pound-Drever-Hall Feedforward

TL;DR

This paper presents an adaptive PDH feedforward technique that significantly suppresses high-frequency laser phase noise, achieving over 40 dB noise reduction up to 50 MHz, enhancing laser stability for quantum and metrological applications.

Contribution

It introduces an adaptive control circuit for PDH feedforward, improving long-term stability and robustness of high-frequency laser phase noise suppression.

Findings

Achieved ≥40 dB phase noise suppression around 2 MHz

Demonstrated noise suppression bandwidth up to 50 MHz

Compared robustness with traditional feedback methods

Abstract

Suppressing high-frequency laser phase noise, particularly at frequencies near and beyond typical feedback bandwidths of a few MHz, is a critical yet challenging task in many advanced applications. Feedforward-based methods generally outperform feedback in high-frequency range, but their performances are more susceptible to perturbations. In this work, we focus on the Pound-Drever-Hall (PDH)-feedforward method we demonstrated recently [Yu-Xin Chao et al., Optica 11(7), 945-950 (2024)] and analyze the factors that affect its long-term stability. By constructing a simple circuit allowing for adaptive control of the feedforward gain in response to power fluctuations of cavity transmission, we demonstrate a robust $\geq 40$ dB suppression of laser phase noise around 2 MHz and a noise suppression bandwidth up to 50 MHz. In comparison, when using normal PDH feedback, robust noise suppression of over 40 dB can only occur for frequencies below tens of kHz in most setups. Our findings may pave the way for general usage of PDH feedforward and allow for simple construction of low-noise lasers for precise quantum controls and precision metrology.