Synthetic FM triplet for AM-free precision laser stabilization and spectroscopy

TL;DR

This paper introduces an improved PDH laser stabilization scheme using an acousto-optic modulator for digital phase reference generation, achieving better control of residual amplitude modulation and enhanced flexibility over traditional methods.

Contribution

The authors develop a simplified, reconfigurable PDH scheme with digital synthesis, enabling superior residual amplitude modulation control and easier implementation compared to electro-optic modulator-based systems.

Findings

Enhanced residual amplitude modulation suppression

Flexible digital synthesis of modulation tones

Improved control over optical field quadratures

Abstract

The Pound-Drever-Hall (PDH) cavity-locking scheme has found prevalent uses in precision optical interferometry and laser frequency stabilization. A form of frequency modulation spectroscopy, PDH enjoys superior signal-to-noise recovery, large acquisition dynamic range, wide servo bandwidth, and robust rejection of spurious effects. However, residual amplitude modulation at the signal frequency, while significantly suppressed, still presents an important concern for further advancing the state-of-the-art performances. Here we present a simplified and improved scheme for PDH using an acousto-optic modulator to generate digital phase reference sidebands instead of the traditionally used electro-optic modulator approach. We demonstrate four key advantages: (1) the carrier and two modulation tones are individually synthesized and easily reconfigured, (2) robust and orthogonal control of the modulated optical field is applied directly to the amplitude and phase quadratures, (3) modulation synthesis, demodulation, and feedback are implemented in a self-contained and easily reproducible electronic unit, and (4) superior active and passive control of residual amplitude modulation is achieved, especially when the carrier power is vanishingly low. These distinct merits stimulate new ideas on how we optimally enact PDH for a wide range of applications.