Nonlinear Stabilization of High-Energy and Ultrashort Pulses in Passively Modelocked Lasers with Fast Saturable Absorption

TL;DR

This paper demonstrates that the cubic-quintic modelocking equation (CQME) predicts stable high-energy ultrashort pulses in passively modelocked lasers, surpassing the stability range of the Haus modelocking equation (HME), and aligns with experimental observations.

Contribution

It shows that including a quintic nonlinearity in the CQME yields stable high-energy pulses, extending the stability range beyond the HME predictions.

Findings

CQME predicts stable high-energy pulses with small quintic terms.

Stability range of CQME exceeds that of HME.

Results align with experimental data.

Abstract

The two most commonly used models for passively modelocked lasers with fast saturable absorbers are the Haus modelocking equation (HME) and the cubic-quintic modelocking equation (CQME). The HME corresponds to a special limit of the CQME in which only a cubic nonlinearity in the fast saturable absorber is kept in the model. Here, we use singular perturbation theory to demonstrate that the CQME has a stable high-energy solution for an arbitrarily small but non-zero quintic contribution to the fast saturable absorber. As a consequence, we find that the CQME predicts the existence of stable modelocked pulses when the cubic nonlinearity is orders of magnitude larger than the value at which the HME predicts that modelocked pulses become unstable. This intrinsically larger stability range is consistent with experiments. Our results suggest a possible path to obtain high-energy and ultrashort pulses by fine tuning the higher-order nonlinear terms in the fast saturable absorber.