Abstract

An automated technique has been developed for the analysis of various types of interferograms. The technique makes use of a high speed digitized microdensitometer to scan the interferograms and a high speed computer to perform the required computations. The optical thickness variations for a test specimen can be determined by analysis of one or two interferograms. In addition, when required, determinations can be made of time change in optical thickness or the physical thickness and index of refraction homogeneity profiles by analysis of multiple interferograms.

© 1968 Optical Society of America

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Figures (5)

Fig. 1
Fig. 1

Block diagram for the determination of the reference scan.

Fig. 2
Fig. 2

Interferogram corresponding to the empty interferometer.

Fig. 3
Fig. 3

Interferogram corresponding to the interferometer–test piece combination.

Fig. 4
Fig. 4

Computer determined fringe positions for the interferogram–test piece combination.

Fig. 5
Fig. 5

Results of applying the double interferogram procedure on two different interferograms corresponding to the same test piece having λ/4 variations.

Equations (24)

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L = M λ ,
Δ L = ( H / D ) λ ,
Case I             Δ L = 2 ( n - 1 ) Δ t             Transmittance interferometer ,
Case II             Δ L = 2 n Δ t             Fizeau interferometer ,
Case III Δ L = 2 Δ t             Reflecting test piece ,
V = Δ t / 2 = H / 2 D K ,
S ¯ = ( P L - P F ) / ( N - 1 ) ,
A = S i + S i - 1
B = S i + S i + 1 .
X I J = A + I D + J B ,
I = 1 N J = 1 M ( P I J - X I J ) 2
H I J = P I J - X I J
E P = Δ X / 2 ,
Δ X L / N X
L N F · D ,
E P N F D / 2 N X .
Δ t = H λ / 2 D K
E S = E p λ / 2 D K .
E S N F λ / 4 N X K .
E D N F λ / 2 N X K .
Tranmission interferometer             Δ L T = 2 [ ( n - 1 ) Δ t + t Δ n ]
Fizeau interferometer             Δ L F = 2 [ n Δ t + t Δ n ] ,
Δ t = 1 2 ( Δ L F - Δ L T ) ,
Δ n = [ ( Δ L T - 2 ( n - 1 ) Δ t ] / 2 t .

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