Influence of spectral filtering on the quantum nature of light

We study the two-time correlation function of spectrally filtered light fro m a quantum mechanical light source. The bunching and anti-bunching propert ies of the photo-statistics of a field display the quantum nature of the so urce. We study whether these properties are affected by the presence of fil ters that are modelled by dielectric slabs. We quantize the radiation field in the presence of the filters and express the correlation function in ter ms of source operators. As a quantum source we take the resonance fluoresce nce of a driven two-level atom. We find that the spectral correlations depe nd on the linewidth of the filters. When the pass time of the filter is muc h longer than the time scale on which the source evolves, the presence of t he filter can conceal the quantum nature of the source. However. quantum me chanical correlations between opposite side bands survive even for very nar row filters.