## 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*′ ± Δ*d*′, either two known precise wavelengths satisfying the requirement of |4(1/λ_{2} − 1/λ_{1})Δ*d*′| ≤ 1 or three known precise wavelengths satisfying the requirement of 1 < |4(1/λ_{2} − 1/λ_{1})Δ*d*′| ≤ *n* are sufficient for finding the correct integral orders. I take the integral part of either 2(*d*′ + Δ*d*′)/λ_{1} or 2(*d*′ − Δ*d*′)/λ_{1} as *m*_{11}′, continue using *m*_{12}′ + *e*_{2}′ = (*m*_{11}′ + *e*_{1})λ_{1}/λ_{2}, point out that the correct *x* in the expression *m*_{11} = *m*_{11}′ + *x* when calculating the correct integral order is the integer nearest (*e*_{2} − *e*_{2}′ − *z*)/(λ_{1}/λ_{2} − 1), give the expression *m*_{12} = *m*_{12}′ + *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

Full Article | PDF Article## Corrections

Zhu Shidong, "Calculation of the integral-order number of interference of a Fabry–Perot interferometer-fringe system: errata," J. Opt. Soc. Am. A**4**, 1838-1838 (1987)

https://www.osapublishing.org/josaa/abstract.cfm?uri=josaa-4-9-1838

**OSA Recommended Articles**

David W. Steinhaus and John V. Kline

J. Opt. Soc. Am. **65**(7) 814-816 (1975)

Shidong Zhu

J. Opt. Soc. Am. A **6**(4) 500-507 (1989)

Carl W. Helstrom

J. Opt. Soc. Am. A **4**(7) 1245-1255 (1987)