Contrast and phase closure acquisitions in photon counting regime using a frequency upconversion interferometer for high angular resolution imaging

In the context of new generation instruments for astronomical interferometer, we have developed in laboratory a new kind of optical interferometer using the frequency conversion of the star light. We investigate the sensitivity limit and reliability of our so-called upconversion interferometer when operating in photon counting mode. For this purpose, we have implemented a laboratory test bench including two three-arm interferometers dedicated to high angular resolution imaging. The first classical one works at the same wavelength as the laboratory star (infrared) and operates with high optical flux levels (used as a reference interferometer). The second one, under test, uses sum frequency generation process in a non-linear optical waveguide placed on each arm to shift the wavelength of the infrared laboratory star to the visible domain. The observables are obtained in photon counting operation, involving signal processing to recover unbiased data. The reference measurement (high flux complex visibilities in infrared) and the upconversion interferometer observables (complex visibilities obtained in photon counting regime) are in good agreement. We notice a degradation on the phase closure terms reliability for low values of the triple product (bispectrum). We estimate from the experimental results the related limiting magnitude for several configurations using an upconversion interferometer.