Patent ID: 7486404

Claim:
A size difference measuring method comprising: an optical interference measuring step without wringing, of obtaining, through simultaneous measurement of interference fringes, size information relating to at least two end standards BG A and BG B which are set in parallel in the measuring optical path between a first interferometer and a second interferometer, by an optical interferometer without wringing that comprises: one light emitter that emits coherent light; a beam splitter; the first interferometer and the second interferometer which are arranged with predetermined separation interval between them and each of which has an optical axis in agreement with the length-measurement axes of at least two end standards BG A and BG B having known preliminary values; and a first interference fringe observation device and a second interference fringe observation device; and a computing step of computing a difference of a size L A , which is the length between the opposing end faces of the end standard BG A and can be expressed by formula 24 below, and a size L B , which is the length between the opposing end faces of the end standard BG B and can be expressed by formula 25 below, (the size difference ΔL AB =L B −L A ), based on the interference fringe phase differences acquired as the size information of the end standards BG A and BG B at the optical interference measuring without wringing step L A =λ/2 {N A +(ε A4 −ε A3 )+(ε A2 −ε A1 )}, (Formula 24) where λ: wave length of the interference light, N A : the integer part of the quotient obtained by dividing the size L A of the end standard BG A by λ/2, (ε A2 −ε A1 ): phase difference between the reference interference fringe and the measured interference fringe relating to one end face of the end standard BG A , observed by the first interference fringe observation device, (ε A4 −ε A3 ): phase difference between the reference interference fringe and the measured interference fringe relating to the other end face of the end standard BG A observed by the second interference fringe observation device, L B =λ/2 {N B +(ε B4 −ε B3 )+(ε B2 −ε B1 )}, (Formula 25) where λ: wave length of the interference light, N B : the integer part of the quotient obtained by dividing the size L B of the end standard BG B by λ/2, (ε B2 −ε B1 ): phase difference between the reference interference fringe and the measured interference fringe relating to one end face of the end standard BG B , observed by the first interference fringe observation device, (ε B4 −ε B3 ): phase difference between the reference interference fringe and the measured interference fringe relating to the other end face of the end standard BG B , observed by the second interference fringe observation device.