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Application of frequency conversion of starlight to high-resolution imaging interferometry. On-sky sensitivity test of a single arm of the interferometer




We investigate the sensitivity of frequency conversion of starlight using a non-linear optical sum frequency process. This study is being carried out in the context of future applications of optical interferometry dedicated to high-resolution imaging. We have implemented a complete experimental chain from telescope to detector. The starlight frequency is shifted from the infrared to the visible using an optically non-linear crystal. To fulfil the requirements of interferometry, our experimental setup uses spatially single-mode and polarization maintaining components. Due to the small size of the collecting aperture (8 inches Celestron C8) with a 3 nm spectral bandwidth, on-sky tests were performed on bright stars in the H band. The detection was achieved in a true photon counting operation, using synchronous detection. Betelgeuse (HMag =−3.9), Antares (HMag =−3.6) and Pollux (HMag =−1) were successfully converted and detected in visible light. Despite the low transmission of our experiment, our results prove that the efficiency of frequency conversion offers sufficient sensitivity for future interferometric applications.