Patent ID: 8184263

Claim:
A measurement apparatus which measures spatial coherence in an illuminated plane illuminated by an illumination system, the apparatus comprising: a measurement mask which has at least three pinholes and is arranged on the illuminated plane; a detector configured to detect an interference pattern formed by lights from said at least three pinholes; and a calculator configured to calculate the spatial coherence in the illuminated plane based on a Fourier spectrum obtained by Fourier-transforming the interference pattern detected by said detector, wherein said calculator calculates spatial coherence Γ p in accordance with: Γ p = 2 ⁢ ⁢ NF p N p ⁢ F 0 where N is the total number of pinholes of said measurement mask, N p is the total number of pinholes which contribute to form an interference pattern with a frequency v of the detected interference pattern, F o is a value of the Fourier spectrum around zero frequency, and F p is a value of the Fourier spectrum around the frequency v.