Gaussian aperture
The element is implemented according to Siegman book “Lasers”, chapter 20.3 “Gaussian apertures and complex ABCD matrices”.
This is a thin optical element consisting of a “soft-aperture” which has a quadratic transversely varying wave-amplitude transmission.
The coefficient α is the total loss factor through an aperture.
See also
Gaussian aperture with thin lens, Elements Matrices, ../catalog, ../elem_props