Apodization

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Apodization literally means "removing the foot". It is the technical term for changing the shape of a mathematical function, an electrical signal, an optical transmission or a mechanical structure. An example of apodization is the use of the Hann window in the Fast Fourier transform analyzer to smooth the discontinuities at the beginning and end of the sampled time record.

In optical design jargon, an apodization function is used to purposely change the input intensity profile of an optical system, and may be a complicated function to tailor the system to certain properties. Usually it refers to a non-uniform illumination or transmission profile that approaches zero at the edges. The diaphragm of a photo camera is not strictly an example of apodization, since the stop doesn't produce a smooth transition to zero intensity, nor does it provide shaping of the intensity profile (beyond the obvious all-or-nothing, "top hat" transmission of its aperture). Simulation of a gaussian laser beam input profile is an example of apodization.

Apodization is used in telescope optics in order to improve the dynamic range of the image. For example, stars with low intensity in the close vicinity of very bright stars can be made visible using this technique. Generally, apodization reduces the resolution of an optical image; however, because it reduces diffraction edge effects, it can actually enhance certain small details.

Photon sieves provide a relatively easy way to achieve tailored optical apodization.^[1]