Coherent feedback from dissipation: the lasing mode volume of random lasers

TL;DR

This paper demonstrates that random lasers with high dissipation can still exhibit coherent feedback, with a finite lasing mode volume influenced by pump intensity, explained through a new theoretical model.

Contribution

The study introduces a theory showing how lossy dynamics in random lasers lead to a finite lasing mode volume, resolving the puzzle of coherence without resonators.

Findings

Random lasers can exhibit coherent feedback despite high dissipation.

Lasing mode volume depends on pump intensity as predicted by the theory.

The theory aligns with experimental observations of photon statistics and mode volume.

Abstract

In any quantum or wave system dissipation leads to decoherence. Therefore, it was surprising in first instance when experiments on strongly lossy random lasers showed unambiguously by measurements of the photon statistics and of the lasing mode volume that coherent feedback is possible in such systems3-5,8. In coherent-feedback lasers the photons form a far-from-equilibrium condensate in the sense that a single quantum state is occupied by a macroscopic number of photons15. We demonstrate that the lossy dynamics of random lasers alone imply a three dimensional finite lasing mode extent, thus resolving the puzzle about coherent feedback without resonator. Our theory of random lasing including nonlinear gain and gain saturation predicts a characteristic dependence of this lasing mode volume on the pump intensity, which can be tested experimentally.