Patent ID: 8922786

Claim:
A detector comprising: an illumination optical system configured to illuminate a first grating having a period in each of a first direction and a second direction different from the first direction, and a second diffraction grating having a period in the second direction different from the period of the first diffraction grating in the second direction; and a detection optical system configured to detect diffracted light diffracted by the first diffracted grating and the second diffraction grating illuminated by said illumination optical system, said detection optical system including a photoelectric conversion element and a guide portion arranged on a pupil plane of said detection optical system, wherein said illumination optical system forms a first pole and a second pole on a pupil plane thereof, the guide portion is configured to guide, to the photoelectric conversion element, the light diffracted by the first diffracting grafting and the second diffraction grating by illuminating the first diffraction grating and the second diffraction grating with the light from the first pole at an oblique incidence in the first detection, and the diffracted light diffracted by the second diffraction grating by illuminating the first diffracting grating and the second diffracting grating with the light from the second pole at an oblique incidence in the second direction enters a position different from the guide portion on the pupil plane of the detection optical system.