Clearer visibility Hong-Ou-Mandel effect with correlation function based   on rates rather than intensities
  We test ideas put forward e.g in arXiv:1508.02368, which suggest that using rates in quantum optics can lead to better indicators of non-classicality for states of quantum optical fields with undefined photon numbers. By rate we mean the ratio of registered photons in a given detector to the total number of detected photons in all detectors in the experiment. For the Hong-Ou-Mandel effect for parametric down conversion fields, we show that by using two detector correlation functions which are defined in terms of averages of products of measured rates, rather than usual intensities, one can observe non -- classical visibilities beyond $1/2$ for significantly higher pump rates. At such rates we already have a partially stimulated emission which leads to significant amplitudes for multiple pairs production, still the new approach allows to clearly see the non-classical dip. 
Krzysztof Roso{\l}ek, Kamil Kostrzewa, Arijit Dutta, Wies{\l}aw   Laskowski, Marcin Wie\'sniak, Marek \.Zukowski
quant-ph