Experimental Results of the Coherent Differential Imaging on Speckle Area Nulling (CDI-SAN) Method

Direct detection of Earth-like exoplanets requires a high-contrast imaging system to suppress bright stellar light that prevents the detection. The wavefront sensing and control technique which is one component of the high-contrast imaging system can suppress stellar scattered light (speckles) caused by wavefront aberrations. However, deformation of the system due to temperature changes in space telescopes or atmospheric turbulence in ground-based telescopes cause speckles that fluctuate faster than the wavefront sensing and control. As the post-processing technique, the Coherent Differential Imaging on Speckle Area Nulling (CDI-SAN) method was proposed to suppress the fast-fluctuating speckles. We are conducting the laboratory demonstration of the CDI-SAN method using two types of experimental facilities. One of them is equipped with a deformable mirror and a field programmable gate array. In our initial laboratory demonstration, we achieved 10⁻⁸ level contrast. To achieve higher contrast, we are updating our facility. The other facility is equipped with a spatial light modulator (SLM). In this facility, the contrast was improved by 10⁻¹ using the CDI-SAN method.