Patent ID: 8390799

Claim:
A method for measuring optical characteristics of a diffraction optical element, the method comprising: a filtering step of filtering light emitted from a white light source with a band-pass filter, thereby obtaining a beam in a specified wavelength range; a light entering step of allowing the beam in the specified wavelength range to enter an imaging lens composed of the diffraction optical element; a magnifying step of magnifying a spot beam as a result of convergence of the beam by the imaging lens; a projecting step of projecting the magnified spot beam on a photodetector having a plurality of pixels; a measuring step of measuring an intensity of the projected magnified spot beam by using the photodetector while changing a distance between the photodetector and the imaging lens in a direction of an optical axis of the spot beam; and a profile obtaining step of obtaining an intensity variation of the projected magnified spot beam along the optical axis as a function of the distance, the intensity variation including at least two peaks corresponding to two different order diffraction lights.