Exoplanet imaging with a phase-induced amplitude apodization coronagraph. I. Principle

Using two aspheric mirrors, it is possible to apodize a telescope beam without losing light or angular resolution: the output beam is produced by "remapping" the entrance beam to produce the desired light intensity distribution in a new pupil. We present the phase-induced amplitude apodization coronagraph (PIAAC) concept, which uses this technique, and show that it allows efficient direct imaging of extrasolar terrestrial planets with a small-sized telescope in space. The suitability of the PIAAC for exoplanet imaging is due to a unique combination of achromaticity, small inner working angle (about 1.5λ/d), high throughput, high angular resolution, and large field of view. Three-dimensional geometrical ray tracing is used to investigate the off-axis aberrations of PIAAC configurations and show that a field of view of more than 100λ/d in radius is available thanks to the correcting optics of the PIAAC, Angular diameter of the star and tip-tilt errors can be compensated for by slightly increasing the size of the occulting mask in the focal plane, with minimal impact on the system performance. Earth-sized planets at 10 pc can be detected in less than 30 s with a 4 m telescope. Wave-front quality requirements are similar to classical techniques.