Abstract

A modified method of excess fractions used for finding the correct integral orders of interference is given. In this modified method, besides an approximate value of the interferometer spacing d′ ± Δd′, either two known precise wavelengths satisfying the requirement of |4(1/λ₂ − 1/λ₁)Δd′| ≤ 1 or three known precise wavelengths satisfying the requirement of 1 < |4(1/λ₂ − 1/λ₁)Δd′| ≤ n are sufficient for finding the correct integral orders. I take the integral part of either 2(d′ + Δd′)/λ₁ or 2(d′ − Δd′)/λ₁ as m₁₁′, continue using m₁₂′ + e₂′ = (m₁₁′ + e₁)λ₁/λ₂, point out that the correct x in the expression m₁₁ = m₁₁′ + x when calculating the correct integral order is the integer nearest (e₂ − e₂′ − z)/(λ₁/λ₂ − 1), give the expression m₁₂ = m₁₂′ + x − z, introduce integer z into the above-mentioned expressions, and give the selection rules of z. In comparison with the traditional methods, this modified method will avoid both repeatedly probing calculation and using even more wavelengths in measurements and checking computation, and it has rigorous, simple, and convenient features.

© 1987 Optical Society of America

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