Abstract

Quality control of infrared optical elements fabricated from visually opaque materials can be accomplished either during manufacture or after completion by the use of the Evaporograph, a thermal-imaging device. The wavelength range for which the components are designed is used for this inspection. Localized variations in transmittance ranging from 100% to less than 1% are detected and typical examples are shown. The same technique can be applied to the inspection of antireflection coatings. The results obtained are enhanced by the use of suitable filters and examples are shown. Other applications include the inspection of images produced by infrared optical systems, and the determination of birefringence.

© 1962 Optical Society of America

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References

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  1. J. F. W. Herschel, Phil. Trans. Roy. Soc., London 131, 52 (1840).
  2. M. Czerny, Z. Physik 53, 1 (1929).
    [CrossRef]
  3. M. Czerny, P. Mollet, Z. tech. Physik 18, 582 (1937).
  4. Gene W. McDaniel, David Z. Robinson, Appl. Optics 1, 311 (1962).
    [CrossRef]

1962 (1)

Gene W. McDaniel, David Z. Robinson, Appl. Optics 1, 311 (1962).
[CrossRef]

1937 (1)

M. Czerny, P. Mollet, Z. tech. Physik 18, 582 (1937).

1929 (1)

M. Czerny, Z. Physik 53, 1 (1929).
[CrossRef]

1840 (1)

J. F. W. Herschel, Phil. Trans. Roy. Soc., London 131, 52 (1840).

Czerny, M.

M. Czerny, P. Mollet, Z. tech. Physik 18, 582 (1937).

M. Czerny, Z. Physik 53, 1 (1929).
[CrossRef]

Herschel, J. F. W.

J. F. W. Herschel, Phil. Trans. Roy. Soc., London 131, 52 (1840).

McDaniel, Gene W.

Gene W. McDaniel, David Z. Robinson, Appl. Optics 1, 311 (1962).
[CrossRef]

Mollet, P.

M. Czerny, P. Mollet, Z. tech. Physik 18, 582 (1937).

Robinson, David Z.

Gene W. McDaniel, David Z. Robinson, Appl. Optics 1, 311 (1962).
[CrossRef]

Appl. Optics (1)

Gene W. McDaniel, David Z. Robinson, Appl. Optics 1, 311 (1962).
[CrossRef]

Phil. Trans. Roy. Soc., London (1)

J. F. W. Herschel, Phil. Trans. Roy. Soc., London 131, 52 (1840).

Z. Physik (1)

M. Czerny, Z. Physik 53, 1 (1929).
[CrossRef]

Z. tech. Physik (1)

M. Czerny, P. Mollet, Z. tech. Physik 18, 582 (1937).

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Figures (11)

Fig. 1
Fig. 1

Diagram of apparatus to test transmittance.

Fig. 2
Fig. 2

Quantities concerned in transmittance measurements plotted as a function of wavelength. A—Spectral response of evaporograph. B—Spectral radiant intensity of source expressed as a fraction of the spectral radiant intensity from a 200°C black body. C—Spectral transmittance of germanium. D—Effective spectral radiant intensity from 200°C source as seen by the membrane. E—Effective spectral radiant intensity from a 20°C black body as seen by the membrane.

Fig. 3
Fig. 3

Germanium sample with corresponding Evaporograph image.

Fig. 4
Fig. 4

Spectral transmittance of germanium sample measured by infrared spectrophotometer.

Fig. 5
Fig. 5

Evaporograph images of a good and of a defective lens.

Fig. 6
Fig. 6

Germanium window with antireflection coating on both sides of one half.

Fig. 7
Fig. 7

Spectral transmittance of antireflection coating on germanium showing the effect of auxiliary filters. A—Measured transmittance of coated half of germanium. B—Measured transmittance of uncoated half of germanium. C—Effective radiant intensity reaching membrane through coated half of germanium expressed as a fraction of the spectral radiant intensity from a 200°C blackbody. D—Effective radiant intensity reaching membrane through uncoated half of germanium. E—Spectral transmittance of auxiliary glass filter. F—Curve C corrected for filter transmittance. G—Curve D corrected for filter transmittance.

Fig. 8
Fig. 8

Silicon window with antireflection coating on one side of one half only, viewed through glass filter.

Fig. 9
Fig. 9

Diagram of apparatus to test for birefringence.

Fig. 10
Fig. 10

Example of birefringence in sapphire.

Fig. 11
Fig. 11

Example of resolution test of optical system. Line group resolved indicates system resolution of ten lines per millimeter.

Equations (17)

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P s = 0 τ s ( λ ) 1 ( λ ) W λ ( T 2 ) d λ + 0 ρ s ( λ ) W λ ( T 1 ) d λ + 0 s ( λ ) W λ ( T 1 ) d λ
τ s ( λ ) + ρ s ( λ ) + s ( λ ) = 1
ρ s ( λ ) + s ( λ ) = 1 τ s ( λ )
P s = 1 0 τ s ( λ ) W λ ( T 2 ) d λ + 0 [ 1 τ s ( λ ) ] W λ ( T 1 ) d λ
P s = 1 τ s σ T 2 4 + ( 1 τ s ) σ T 1 4
T s ( av ) ( T 1 ) = 0 τ s ( λ ) W λ ( T 1 ) d λ 0 W λ ( T 1 ) d λ
T s ( av ) ( T 2 ) = 0 T s ( λ ) W λ ( T 2 ) d λ 0 W λ ( T 2 ) d λ
U = ( 1 k ) t [ 0 ρ ( λ ) W λ ( T 1 ) d λ + 0 ( λ ) W λ ( T 1 ) d λ + k t 0 1 W λ ( T 2 ) d λ
ρ ( λ ) + ( λ ) = 1
U = k t 1 σ T 2 4 + ( 1 k ) t σ T 1 4
U / t = P = k 1 σ T 2 4 + ( 1 k ) σ T 1 4
W = 1 0 W λ ( T 2 ) d λ
W eff = 1 0 S λ W λ ( T 2 ) d λ
τ s ( av ) = 1 0 τ s ( λ ) S λ W λ ( T 2 ) d λ 0 S λ W λ ( T 2 ) d λ
ρ + = 1 τ m
0.126 × 10 2 τ m + ( 1 τ m ) 1.6 × 10 2 = 1.02 × 1.6 × 10 2
τ m = 0.003.

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