Mid-infrared laser light nulling experiment using single-mode conductive waveguides

Aims. In the context of space interferometry missions devoted to the search for exo-Earths, this paper investigates the capabilities of new single mode conductive waveguides to provide modal filtering in an infrared and monochromatic nulling experiment Methods. A Michelson laser interferometer with a co-axial beam combination scheme at 10.6 mu m is used. After introducing a pi phase shift using a translating mirror, dynamic and static measurements of the nulling ratio are performed in the two cases where modal filtering is implemented and suppressed. No additional active control of the wavefront errors is involved. Results. We achieve on average a statistical nulling ratio of 2.5 x 10(-4) with a 1-sigma upper limit of 6 x 10(-4), while a best null of 5.6 x 10(-5) is obtained in static mode. At the moment, the impact of external vibrations limits our ability to maintain the null to 10 to 20 s. Conclusions. A positive effect of SM conductive waveguide on modal filtering has been observed in this study. Further improvement of the null should be possible with proper mechanical isolation of the setup.