# Spatiotemporal mode-locking in multimode fiber lasers

## TL;DR

This paper demonstrates spatiotemporal mode-locking in multimode fiber lasers, enabling ultrafast pulses with complex mode interactions, opening new avenues for high-power laser applications and nonlinear wave studies.

## Contribution

It introduces a novel method to achieve spatiotemporal mode-locking in multimode fiber lasers using graded-index fibers and intracavity filtering, a previously unexplored regime.

## Key findings

- Successful locking of multiple transverse and longitudinal modes.
- Generation of ultrafast spatiotemporal pulses.
- Observation of multimode nonlinear dynamical processes.

## Abstract

A laser is based on the electromagnetic modes of its resonator, which provides the feedback required for oscillation. Enormous progress has been made in controlling the interactions of longitudinal modes in lasers with a single transverse mode. For example, the field of ultrafast science has been built on lasers that lock many longitudinal modes together to form ultrashort light pulses. However, coherent superposition of many longitudinal and transverse modes in a laser has received little attention. The multitude of disparate frequency spacings, strong dispersions, and complex nonlinear interactions among modes greatly favor decoherence over the emergence of order. Here we report the locking of multiple transverse and longitudinal modes in fiber lasers to generate ultrafast spatiotemporal pulses. We construct multimode fiber cavities using graded-index multimode fiber (GRIN MMF). This causes spatial and longitudinal mode dispersions to be comparable. These dispersions are counteracted by strong intracavity spatial and spectral filtering. Under these conditions, we achieve spatiotemporal, or multimode (MM), mode-locking. A variety of other multimode nonlinear dynamical processes can also be observed. Multimode fiber lasers thus open new directions in studies of three-dimensional nonlinear wave propagation. Lasers that generate controllable spatiotemporal fields, with orders-of-magnitude increases in peak power over existing designs, should be possible. These should increase laser utility in many established applications and facilitate new ones.

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Source: https://tomesphere.com/paper/1705.05050