Notch-Filter Masks: Practical Image Masks for Planet-finding Coronagraphs

An ideal coronagraph with a band-limited image mask can efficiently image off-axis sources while removing identically all of the light from an on-axis source. However, strict mask construction tolerances limit the utility of this technique for directly imaging extrasolar terrestrial planets. We present a variation on the basic band-limited mask design-a family of "notch-filter" masks-that mitigates this problem. These robust and trivially achromatic masks can be easily manufactured by cutting holes in opaque material.