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.

Figure 1

Global scheme of a telescope array using fibered components to analyze the spatial coherence of an astronomical source at visible and infrared wavelengths.

Figure 2

Global scheme of the up-conversion interferometer dedicated to spatial-coherence analysis of an astronomical source (PPLN: periodically poled lithium niobate).

Figure 3

(a) Classical spatial-coherence analysis through a telescope array. (b) Spatial-coherence analysis through the dedicated test bench used for the laboratory experiment on a blackbody source [$P$ (polarizer), $L$ (lens)].

Figure 4

Global scheme of the reference IR interferometer [$P$ (polarizer), OPM (optical path modulation), $L$ (lens), SMF (single mode fiber)].

Figure 5

Global scheme of the up-conversion interferometer [OPM (optical path modulation), $L$ (lens), WDM (wavelength division multiplexer), IF (interference filter), Pr (prism), $P$ (polarizer)].

Figure 6

Fringe contrast evolution versus the fiber tip relative position $x$ for the two experimental configurations [red crosses (reference IR interferometer measurements), black crosses (up-conversion interferometer measurements)]. The red curve is the numerical fit of the reference contrast measurements. The black curve is the numerical fit of the SFG contrast measurements.