Statistical physics of power fluctuations in mode locked lasers

TL;DR

This paper analyzes power fluctuations in passively mode locked lasers using statistical physics, deriving explicit formulas for fluctuations and their relations, revealing Gaussian behavior and non-perturbative characteristics.

Contribution

It introduces a non-perturbative statistical light-mode theory approach to analyze power fluctuations in mode locked lasers, providing explicit covariance and fluctuation-dissipation relations.

Findings

Power fluctuations are Gaussian and inversely proportional to the square root of degrees of freedom.

Explicit covariance matrices for pulse, cw, and total power are derived.

Fluctuation-dissipation relations connect fluctuations to steady-state susceptibilities.

Abstract

We present an analysis of the power fluctuations in the statistical steady state of a passively mode locked laser. We use statistical light-mode theory to map this problem to that of fluctuations in a reference equilibrium statistical physics problem, and in this way study the fluctuations non-perturbatively. The power fluctuations, being non-critical, are Gaussian and proportional in amplitude to the inverse square root of the number of degrees of freedom. We calculate explicit analytic expressions for the covariance matrix of the overall, pulse and cw power variables, providing complete information on the single-time power distribution in the laser, and derive a set of fluctuation-dissipation relations between them and the susceptibilities of the steady-state quantities.