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 emission in mesoscale lasers which makes use of a small -amplitude modulation added to the pump. The optimal modulation frequency is obtained from the radio-frequency power spectrum of the unperturbed laser emission. The identification of the lasing onset rests on the appearance of a resonance in the experimentally measured zero-order autocorrelation function (g(2)(0)) plotted as a function of the pump rate. Numerical proof is provided in support of the autocorrelation resonance. The intrinsic simplicity of this technique and its inherent compatibility with photon counting makes it an excellent tool for certifying the onset of laser emission independent of the laser cavity volume. Recently published measurements of g(2)(0), obtained in nanolasers, support the extension of our technique to nanoscale devices.