Towards a Mid-Infrared L Band Up-Conversion Interferometer: First On-Sky Sensitivity Test on a Single Arm

We report on the first on-sky sensitivity test on a single arm of the Astronomical Light Optical Hybrid Analysis (ALOHA) instrument, an uncooled up-conversion interferometer in the L band (3.5 mu m). Despite a low coupling efficiency (in the range of 1 per cent) between the 1-m class telescope and our instrument, we detect a magnitude L-mag = 2.8 star with a signal-to-noise ratio SNR = 2.7 over a 30 min integration time and with a spectral resolution lambda/Delta lambda = 100. As the ALOHA project aims to shift light from the L band to the near-infrared, the use of very low loss silica optical fibres is an important step towards fibre-linked very long-baseline interferometry in the mid-infrared.