Amplitude Noise Suppression in Frequency-Doubled Lasers: A Lyapunov Mechanism for Intensity Stabilization in Coupled Oscillator Systems

TL;DR

This paper introduces a Lyapunov-based mechanism for amplitude noise suppression in frequency-doubled lasers, demonstrating significant noise reduction through a novel coupled oscillator dynamics approach.

Contribution

It presents a new Lyapunov functional approach to achieve intensity stabilization in coupled oscillator laser systems, validated experimentally.

Findings

Achieved 100-fold noise contrast in a frequency-doubled Nd:YVO4-LBO laser.

Confirmed the Lyapunov mechanism's role in noise suppression beyond statistical predictions.

Demonstrated the algebraic structure's importance in the noise reduction process.

Abstract

Multimode intracavity frequency-doubled lasers can reach states of amplitude noise suppression orders of magnitude beyond the predictions of independent-mode partition statistics. We show that the chi2 coupled-wave dynamics in the doubling crystal admit a Lyapunov functional whose monotone decrease under each crystal pass establishes a constant-intensity manifold as the per-pass descent target of the mode dynamics. We confirm the mechanism in an intracavity frequency-doubled Nd:YVO4-LBO laser, observing a 100 fold contrast between full and Fabry-Perot-filtered output noise at fixed detector bandwidth, well beyond the statistical-averaging baseline. The mechanism rests on the algebraic structure of the coupling, a coherent superposition of oscillators sharing a quadratic dissipative channel, and is therefore a candidate for analogous noise-suppression effects in other coupled oscillator systems with the same algebraic form.