Laboratory demonstration of spatial-coherence analysis of a blackbody through an up-conversion interferometer.

In the field of high resolution imaging in astronomy, we experimentally demonstrate the spatial-coherence analysis of a blackbody using an up-conversion interferometer in the photon counting regime. The infrared radiation of the blackbody is converted to a visible one in both arms of the interferometer thanks to the sum-frequency generation processes achieved in Ti-diffused periodically poled lithium niobate waveguides. The coherence analysis is performed through a dedicated imaging stage which mimics a classical telescope array analyzing an astrophysical source. The validity of these measurements is confirmed by the comparison with spatial-coherence analysis through a reference interferometer working at infrared wavelengths.