Pound-Drever-Hall Feedforward: Laser Phase Noise Suppression beyond Feedback

TL;DR

This paper presents a feedforward technique that significantly enhances laser phase noise suppression beyond traditional PDH feedback, achieving four orders of magnitude improvement at high frequencies.

Contribution

The authors introduce a novel feedforward method that recycles the residual PDH signal to suppress high-frequency laser phase noise more effectively than feedback alone.

Findings

Achieves about 10,000 times better phase noise suppression at MHz frequencies.

Demonstrates noise suppression comparable to cavity filtering.

Applicable to high-stability lasers for quantum control applications.

Abstract

Pound-Drever-Hall (PDH) laser frequency stabilization is a powerful technique widely used for building narrow-linewidth lasers. This technique is however ineffective in suppressing high-frequency (>100~kHz) laser phase noise detrimental for many applications. Here, we introduce an effective method which can greatly enhance its high-frequency performance. The idea is to recycle the residual PDH signal of a laser locked to a cavity, by feedforwarding it directly to the laser output field after a delay fiber. Using this straightforward method, we demonstrate a phase noise suppression capability about 4 orders of magnitude better than just using usual PDH feedback for phase noise around a few MHz. We further find that this method exhibits noise suppression performance equivalent to cavity filtering. The new method holds great promise for applications demanding highly stable lasers with diminished phase noise up to tens of MHz, e.g. precise and high-speed control of atomic and molecular quantum states.