Photon statistics measurement by use of single photon detection

The direct measurement of the Mandel parameter of weak laser pulses, with 10 ns pulse duration time and the mean number of photon per pulse (n) over bar being approximately 0.1, is investigated by recording every photocount event. With the Hanbury Brown and Twiss detection scheme, and not more than one photon per pulse being detected during the sample time by single-photon counters, we have found that the single mode diode laser with driving current lower than the threshold yields a sub-Poissonian statistics. In addition, when the diode laser driving current is much higher than the threshold, it is validated that the Mandel parameter Q(C) of the Poissonian coherent state is nearly -(n) over bar /2. The experimental results are in good agreement with theoretical prediction considering the measurement error.