Onset of Lasing in Small Devices: The Identification of the First Threshold through Autocorrelation Resonance

We present a simple technique for identifying the onset of coherent emissionin mesoscale lasers which makes use of a small -amplitude modulation addedto the pump. The optimal modulation frequency is obtained from theradio-frequency power spectrum of the unperturbed laser emission. Theidentification of the lasing onset rests on the appearance of a resonance in theexperimentally measured zero-order autocorrelation function (g(2)(0)) plottedas a function of the pump rate. Numerical proof is provided in support of theautocorrelation resonance. The intrinsic simplicity of this technique and itsinherent compatibility with photon counting makes it an excellent tool forcertifying the onset of laser emission independent of the laser cavity volume.Recently published measurements of g(2)(0), obtained in nanolasers, supportthe extension of our technique to nanoscale devices.