Patent Number: 
Section: claims

1. A measuring apparatus, comprising:light receiving means for receiving EUV light diverging from a light convergent point;an optical system for directing the EUV light toward said light receiving means;a first light blocking member disposed at a pupil plane of said optical system and having a plurality of openings;a second light blocking member having an opening and being detachably mountable at the position of the light convergence point: andmeans for detecting a spatial distribution of the EUV light at the light convergent point, on the basis of reception of EUV light by said light receiving means. 2. An apparatus according to claim 1, wherein, when L is the distance between the light convergent point and the openings, λ is the wavelength of light to be measured, and R is a desired resolving power, the size d of the openings of the first light blocking member satisfies a relation d>1.22·λ·L/R. 3. An apparatus according to claim 1, wherein, when L is the distance between the light convergent point and the openings, λ is the wavelength of light to be measured, and D is a diameter of the light convergent point, the size d of the openings of the first light blocking member satisfies a relation d>6.1·λ·L/D. 4. An apparatus according to claim 1, wherein said second light blocking member has a thickness in an optical axis direction and wherein the opening of said second light blocking member has extension from an incidence direction of the EUV light to an exit direction thereof, with a predetermined angle. 5. A measuring apparatus, comprising:light receiving means for receiving EUV light diverging from a light convergent point;a gas filter disposed in a portion of a light path of the EUV light and being filled with a predetermined gas; andmeans for detecting a spatial distribution of the EUV light at the light convergent point, on the basis of the reception of EUV light by said light receiving means. 6. An apparatus according to claim 5, wherein the gas is a mixed gas comprising mixture of gases having positive and negative differential coefficients, to wavelength, of an absorption coefficient with respect to light of a predetermined wavelength. 7. An apparatus according to claim 5, wherein the gas consists of at least one of xenon Xe, sulfur hexafluoride SF6, krypton Kr, and mixture of them. 8. An apparatus according to claim 5, further comprising a light blocking member having an opening and being detachably mountable at the position of the light convergence point. 9. An apparatus according to claim 8, wherein said light blocking member has a thickness in an optical axis direction and wherein the opening of said second light blocking member has extension from an incidence direction of the EUV light to an exit direction thereof, with a predetermined angle.