geometric extent

G

quantity that determines the maximum geometric throughput of radiation transmitted, received or emitted in a single-pass, passive optical arrangement

Note 1 to entry: Defining a ray as the confined radiation exchange between two subtended surface area elements dA and dA′ at distance l, with normal vectors and and orientation angles θ and θ ′ with respect to a common optical axis, the geometric extent is equal to the action of all possible rays between both surface areas A and A′. This is expressed by the integral over the product of all projected area elements dA cosθ and dA′ cosθ ′ weighted by the distance squared to account for the apparent size of the subtending surfaces areas:

with

where dΩ and dΩ ′ are the solid angle elements defining the angular extent of dA′ from dA and dA from dA′ respectively.

Note 2 to entry: "Single-pass" means that the term applies only for radiation transfer in a single defined direction. It does not apply to devices such as Fabry–Pérot cavities.

Note 3 to entry: See also "optical extent".

Note 4 to entry: The geometric extent is expressed in square metre times steradian (m²·sr).

Note 5 to entry: This entry was numbered 845-01-33 in IEC 60050-845:1987.

Note 6 to entry: This entry was numbered 17-489 in CIE S 017:2011.