Multiwavelength imaging concepts for exoplanet detection

Abstract

Direct exoplanet detections are currently limited by speckle noise arising from residual atmospheric wavefront errors and optical aberrations. Simultaneous spectral differential imaging (SSDI) is a high contrast imaging technique that aims at reducing this noise by the subtraction of images obtained simultaneously in adjacent narrow spectral bands. SSDI performances are severely degraded by differential optical aberrations between channels. We discuss two novel approaches to implement SSDI in which there are no differential aberrations. The first uses a microlens array at the focal plane to sample the point spread function (PSF) and micro-filters on the backside of each microlens to separate colors. The micropupils are immediately imaged on the detector. The second preserves the microlens array at the focal plane but re-images the array of micropupils through a beam-splitter on the detector. In both concepts the PSF measurement is made at the microlens array, so all optics is common prior to the PSF measurement in all colors. A simple prototype was used to test the concepts; preliminary results yield noise attenuation of ~10 -2 .