First laboratory demonstration of iEFC for high-contrast imaging at small angular separation on ELT scales

Implicit electric field conjugation (iEFC) is an efficient, model-free wavefront control technique for dark hole creation. Because it relies on calibration with real data rather than a synthetic model of the instrument, iEFC is uniquely versatile and has been demonstrated in the laboratory and on-sky with different experimental platforms and coronagraphs.

Prior iEFC demonstrations produced dark holes with moderate to large inner working angles and wide fields of view, often extending over several tens of λ/D. Here, the authors report the first iEFC demonstration at small angular separations, achieving a dark hole spanning 1 to 4 λ/D on a segmented pupil in H-band under laboratory conditions; this aggressive inner working angle and reduced field of view highlight the uniqueness of the SPEED facility.

SPEED (segmented pupil experiment for exoplanet detection) is a high-contrast imaging testbed designed for extremely large telescopes (ELTs), developed in the context of the ELT/PCS instrument (planetary camera and spectrograph), currently in pre-phase A. Its small-inner-working-angle coronagraph, an apodized pupil complex mask coronagraph (APCMC), and its multi- and out-of-pupil-plane deformable mirror (DM) architecture are specifically optimized for dark holes at very small inner working angles, down to the diffraction limit.

The results demonstrate (i) that widely separated out-of-pupil DMs are well suited to generating dark holes with inner working angles down to 1 λ/D, and (ii) that iEFC is effective when combined with the SPEED wavefront control architecture for high-contrast imaging with segmented telescopes. Ultimately, the work paves the way toward meeting the stringent high-contrast requirements of ELT-class instruments and opens new opportunities for exoplanet detection at unprecedented angular resolutions.