Patent ID: 8542345
Filing Date: 2013-09-24
Classification: G01M,G03B,G03F

Abstract:
1. A measurement apparatus which measures a numerical aperture NA of an optical system to be measured, the measurement apparatus comprising: a mirror configured to reflect test light which passes through the optical system; an interferometer unit which includes an image sensor and is configured to form an interference fringe on an image sensing plane of the image sensor by reference light and the test light reflected by the mirror; and a controller configured to control the interferometer unit, and to compute the numerical aperture NA of the optical system based on the interference fringe captured by the image sensor, wherein the controller is configured to compute the numerical aperture NA of the optical system by multiplying a quotient ΔNA/ΔR, describing a change ΔNA in the numerical aperture NA of the optical system with respect to a change ΔR in pupil radius R of the optical system in the image sensing plane, by the pupil radius R of the optical system in the image sensing plane, wherein the controller is configured to compute, using a first radius R to compute, using a second radius R to compute the quotient ΔNA/ΔR using the following equation: