Halftoning: from the printing industry to high-contrast imaging instruments
P. Martinez, C. Dorrer, M. Kasper, A. Boccaletti, and K. Dohlen
ESO, LESIA, LAM
Controlling the amplitude of light is crucial for many scientific applications, such as imaging systems, astronomical instruments, optical testing, or laser physics. We provide an overview of the halftoning technique – the technique used for hundred years in the printing industry as the process of generating a continuous tone image with only black and white dots – for application to coronagraphy. Customized filters with spatially varying transmission are produced using a binary array of metal pixels (namely microdot masks) that offers excellent control of the local transmission, with intrinsic achromaticity property. Applications, design guidelines, and testing of near-IR prototypes for both pupil (Apodized Pupil Lyot Coronagraphs) and focal plane (Band-Limited Coronagraphs) devices are presented in the context of the VLT-SPHERE and E-ELT EPICS instruments.