Mode Locking At and Below the CW Threshold

TL;DR

This paper demonstrates a new regime in a Ti:Sapphire laser where mode locking occurs below the CW threshold, enabling pulsed operation without CW oscillation by exploiting a Kerr nonlinearity 'sweet spot'.

Contribution

It introduces a novel regime for mode locking below the CW threshold and explains the underlying mechanism with a qualitative model.

Findings

Pulsed operation can be achieved without CW oscillation.

The Kerr nonlinearity 'sweet spot' optimizes mode locking.

Pump power threshold for mode locking is significantly lowered.

Abstract

We explore experimentally a new regime of operation for mode locking in a Ti:Sapphire laser with enhanced Kerr nonlinearity, where the threshold for pulsed operation is lowered below the threshold for continuous-wave (CW) operation. Even though a CW solution cannot exist in this regime, pulsed oscillation can be realized directly from zero CW oscillation. In this regime, the point of maximum strength of the Kerr nonlinear process provides a "sweet spot" for mode locking, which can be optimized to considerably lower the pump power threshold. The properties of the "sweet spot" are explained with a qualitative model.