apodizers

An apodizer is an optical element or device that modifies the amplitude and/or phase of light across an optical pupil or beam to control the diffraction pattern of an imaging system. By shaping the wavefront, apodizers suppress diffraction sidelobes and reduce stray light in the image, often at the expense of some throughput and potential bandwidth sensitivity. They are widely used in high-contrast astronomical imaging, where suppressing starlight enables the direct detection of faint companions such as exoplanets, as well as in laser beam shaping and optical lithography.

There are several classes of apodizers. Amplitude apodizers implement a transmission profile across the pupil, often smooth functions such as Gaussian, cosine, or polynomial ramps, or binary masks produced by lithographic processes. Phase apodizers modify the wavefront phase to achieve similar redistribution of energy. Pupil-plane apodizers can be static, designed for a particular wavelength or bandwidth. Phase-Induced Amplitude Apodization (PIAA) uses refractive or diffractive optics to remap the pupil illumination, achieving high throughput with reduced diffraction, while shaped-pupil methods design masks to create dark zones in the PSF for coronagraphy.

Applications include coronagraphic instruments and high-contrast imagers in ground-based and space telescopes. The selection of an apodizer involves trade-offs among throughput, bandwidth, inner working angle, and manufacturing complexity.