What is the "working aperture" of MMDM

The reflective surface of an MMDM is a membrane, which is fixed at the edges. Thus for correction of an aberration with arbitrary boundary conditions, a central part of the mirror (approximately 2/3 of the total membrane diameter) should be used. This area is called "working aperture" of the mirror. Thus, for a 15 mm MMDM, a working aperture is about 10 mm.

 

Any membrane or coating defect located outside the working aperture does not affect the mirror performance.