Threshold in nanolasers: definitions, measurement, modelling and applications – Invited Paper

Coherence, associated to the crossing of laser threshold, identifies lasing and is the defining property for most of the current laser applications. It is signalled by the change between Gaussian and Poissonian photon statistics. The threshold is poorly defined in nanolasers, where the transition between the two statistical regimes takes place over a broad pump range. This has led to confusion about the nanoscale threshold definition, as well to inconsistencies depending on the measurement techniques. A proper identification of the coherence onset depends on a more sophisticated modelling approach, where the properties of radiation “below” and “above” threshold are simultaneously taken into account. Furthermore, the mixed regime of emission holds promise for interesting and new applications.