Thermal photon statistics in laser light above threshold

We show that the reduction in photon number fluctuations at laser threshold often cited as a fundamental laser property does not occur in small semiconductor lasers. The conventional theory of threshold noise is not valid in lasers with a spontaneous emission factor larger than 10. If the spontaneous emission factor is larger than 10, the photon number statistics even remain thermal far above threshold. We therefore conclude that the reduction in photon number fluctuations is not a fundamental laser property but rather a matter of size and the corresponding relative importance of quantum fluctuations above threshold.