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Abstract

A photon-number-resolving transition edge sensor (TES) is used to measure the photon-number distribution of two microcavity lasers. The investigated devices are bimodal microlasers with similar emission intensity and photon statistics with respect to the photon autocorrelation. Both high-beta microlasers show partly thermal and partly coherent emission around the lasing threshold. For higher pump powers, the strong mode of microlaser A emits Poissonian distributed photons, while the emission of the weak mode is thermal. By contrast, laser B shows a bistability resulting in overlayed thermal and Poissonian distributions. While a standard Hanbury Brown and Twiss experiment cannot distinguish between the simple thermal emission of laser A and the temporal mode switching of the bistable laser B, TESs allow us to measure the photon-number distribution, which provides important insight into the underlying emission processes. Indeed, our experimental data and their theoretical description by a master equation approach show that TESs are capable of revealing subtle effects like the mode switching of bimodal microlasers. As such, we clearly demonstrate the benefit and importance of investigating nanophotonic devices via photon-number-resolving transition edge sensors.