First On-Sky Fringes with an Up-Conversion Interferometer Tested on a Telescope Array

The Astronomical Light Optical Hybrid Analysis project investigates the combined use of a telescope array interferometer and nonlinear optics to propose a new generation of instruments dedicated to high-resolution imaging for infrared astronomy. The nonlinear process of optical frequency conversion transfers the astronomical light to a shorter wavelength domain. Here, we report on the first fringes obtained on the sky with the prototype operated at $1.55\mu \mathrm{m}$ in the astronomical $H$ band and implemented on the Center for High Angular Resolution Astronomy telescope array. This seminal result allows us to foresee a future extension to the challenging midinfrared spectral domain.

Figure 1

On-site configuration with implementation of the ALOHA prototype at $1.55\mu \mathrm{m}$ on the CHARA Array. It is composed of three different stages (infrared, SFG, and visible stages). Apart from the filtering stage, the interferometer is entirely fibered with single-mode and polarization maintaining fibers.

Figure 2

Experimental power spectral density related to the $\alpha$ UMa interferogram. Black: interferometric configuration, blue and orange: photometric signals, red: interferometric configuration without signal source.

Figure 3

Comparison of the signal-to-noise ratio measured in interferometric and in photometric configurations. In the photometric configurations, the flux level is measured by injecting the light in one single arm, one after the other, and then without light injection at the input of the interferometer.

Figure 4

Future design for the midinfrared domain. The light collected by the telescopes are up-converted in nonlinear crystals as close as possible to the telescope foci, before being mixed thanks to a fibered coupler.