The mode-locking transition of random lasers

TL;DR

This paper demonstrates spontaneous mode-locking in micron-sized random lasers, showing a transition from weakly to strongly interacting modes, and introduces a novel mode-selective pumping mechanism for miniaturized, all-optically controlled light sources.

Contribution

It reveals spontaneous mode-locking in disordered micrometer-scale lasers and introduces a new mode-selective pumping method to control mode interactions.

Findings

Mode-locking occurs spontaneously in random lasers.

A mode transition from weakly to strongly interacting regimes is demonstrated.

The smallest mode-locking device has been fabricated.

Abstract

The discovery of the spontaneous mode-locking of lasers, i.e., the synchronous oscillation of electromagnetic modes in a cavity, has been a milestone of photonics allowing the realization of oscillators delivering ultra-short pulses. This process is so far known to occur only in standard ordered lasers with meter size length and only in the presence of a specific device (the saturable absorber). Here we demonstrate that mode-locking can spontaneously arise also in random lasers composed by micronsized laser resonances dwelling in intrinsically disordered, self-assembled clusters of nanometer-sized particles. Moreover by engineering a novel mode-selective pumping mechanism we show that it is possible to continuously drive the system from a configuration in which the various excited electromagnetic modes oscillate in the form of several, weakly interacting, resonances to a collective strongly interacting regime. By realizing the smallest mode-locking device ever fabricated, we open the way to novel generation of miniaturized and all-optically controlled light sources.