Patent ID: 8842294

Claim:
A detection apparatus, comprising: an illumination optical system configured to illuminate a first diffraction grating having periods in each of a first direction and a second direction different from the first direction, and a second diffraction grating having a period different from the period in the second direction of the first diffraction grating in the second direction, at an oblique incidence; and a detection optical system configured to detect diffracted light from the first diffraction grating and the second diffraction grating, wherein the illumination optical system includes a first pole and a second pole which is in opposite side of the first pole with respect to an optical axis on a pupil plane thereof, and wherein the detection optical system detects the light diffracted by the first diffraction grating and the second diffraction grating by illuminating the first diffraction grating and the second diffraction grating with the light from the first pole and the second pole at an oblique incidence in the first direction radiated from the illumination optical system.