Beam Quality Factor of Single-Mode Gain-Guided Fiber Lasers

TL;DR

This paper derives a closed-form expression for the beam quality factor M^2 of gain-guided fiber lasers, revealing that the M^2 value can be arbitrarily large, impacting the interpretation of experimental results.

Contribution

It provides a novel analytical formula for M^2 in gain-guided fibers, enhancing understanding of beam quality in such lasers.

Findings

M^2 can be arbitrarily large in gain-guided fiber lasers

Derived a closed-form expression for M^2 as a function of the generalized V-number

Implications for interpreting beam quality measurements in experiments

Abstract

The beam quality factor M^2 for the fundamental LP01 mode of a step-index fiber is calculated in the presence of gain, in a closed form, as a function of the complex generalized V-number. It is shown that the M^2 value of a single-mode gain-guided fiber laser can be arbitrary large. The results are important for the interpretation of the beam quality measurements in recent experiments on single-mode gain-guided fiber lasers.