Abstract

The construction and performance of three far-infrared spectrometers are described. These are a large-aperture diffraction-grating monochromator using six 28×35-cm interchangeable echelette gratings to span the frequency range from 10 to 150 cm−1, a set of 30-cm-square lamellar grating plates which can be inserted into the grating monochromator to convert it into a lamellar grating interferometer, and an 18-cm Michelson interferometer. The two interferometers are used with an automatic digital data recording system which records the interferograms on punched cards so that the spectra can be obtained by numerical transformation on a digital computer. All three instruments have been operated with the same detector and the same source, thus providing, for the first time, a controlled test of the relative merits of these three types of spectrometers. As expected theoretically, the two interferometers performed similarly except for differences due to beamsplitter efficiency and mechanical accuracy. Owing to their ability to look at all parts of the spectrum simultaneously and to achieve high resolution with large aperture, however, both interferometers proved far superior to the grating spectrometer, giving some of the highest resolution spectra yet obtained in the far-infrared. Examples are presented demonstrating resolution of ∼0.1 cm−1 over the frequency range from 3 to 80 cm−1.

© 1964 Optical Society of America

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References

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  1. See, for example, R. S. Ohl, P. P. Budenstein, and C. A. Burrus, Rev. Sci. Instr. 30, 765 (1959).
    [CrossRef]
  2. For example, see H. Yoshinaga and et al., J. Opt. Soc. Am. 48, 315 (1958);D. Bloor and et al., Proc. Roy. Soc. (London) A260, 510 (1961);V. N. Murzin and A. I. Demshina, Opt. i Spektro-skopiya 13, 826 (1962)[English transl.: Opt. Spectry. 13, 467 (1963)].
    [CrossRef]
  3. For a discussion of the early development of Fourier transform spectroscopy, see J. Strong, J. Opt. Soc. Am. 47, 354 (1957).
    [CrossRef]
  4. J. Strong and G. A. Vanasse, J. Opt. Soc. Am. 49, 844 (1959).
    [CrossRef]
  5. P. Jacquinot, Rept. Progr. Phys. 23, 267 (1960).
    [CrossRef]
  6. J. Connes, Rev. Opt. 40, 45, 116, 171, and 231 (1961).
  7. L. Genzel, J. Mol. Spectry. 4, 241 (1960).
    [CrossRef]
  8. For an interferometer whose limiting aperture subtends a solid angle Ω=πθ2 at a collimating mirror, the axial ray through the interferometer has a path difference cosθ∼1−Ω/2π times that of an extremal off-axis ray. This spread in values, δΔ/Δ, of path difference corresponds to a spread in frequency of δν/ν=δΔ/Δ =Ω/2π, thus limiting the resolving power to values less than R=ν/δν=2π/Ω. Another effect of the finite aperture is that the mean path difference for all rays entering the interferometer is 〈cosθ〉=(1−Ω/4π) times that of an axial ray. Thus, if the axial path difference is used in Eq. (3), the frequencies of spectral elements are overestimated by the factor 1+Ω/4π. For the interferometers described in Secs. III and IV, Ω=4.5×10−4 and 1.8×10−3 sr, respectively. The limitation on resolution is negligible for frequencies below 1000 cm−1, but significant frequency corrections must be made for high-resolution spectra at much lower frequencies.
  9. P. Fellgett, J. Phys. Radium 19, 187, 237 (1958).
    [CrossRef]
  10. Assuming otherwise comparable efficiency for the monochromator and interferometer.
  11. L. Genzel and R. Weber, Z. Angew. Phys. 10, 127 (1957);Z. Angew. Phys. 10, 195 (1958).
  12. A. S. Barker and M. Tinkham, Bull. Am. Phys. Soc. 6, 112 (1961).
  13. E. E. Bell (private communication).
  14. Block Associates, Inc., Cambridge 39, Massachusetts.
  15. H. A. Gebbie and G. A. Vanasse, Nature 178, 432 (1956).
    [CrossRef]
  16. S. Goldman, Information Theory (Prentice-Hall, Inc., Engle-wood Cliffs, New Jersey, 1953), pp. 67 ff.
  17. R. C. Ohlman, P. L. Richards, and M. Tinkham, J. Opt. Soc. Am. 48, 531 (1958).
    [CrossRef]
  18. P. Jacquinot, J. Opt. Soc. Am. 44, 761 (1954).
    [CrossRef]
  19. This design is similar to those used by T. K. McCubbin and W. M. Sinton, J. Opt. Soc. Am. 42, 113 (1952);and by P. L. Richards and M. Tinkham, Phys. Rev. 119, 575 (1960).
    [CrossRef]
  20. The optical system used here can transmit false energy due to double diffraction. Energy at frequencies close to those which pass through the exit slit is roughly focused on the slit jaws or the face of the grating. Part of this energy finds its way back along the optical path, is diffracted by the grating, and irradiates a region around the entrance slit. Since the grating is not, in general, in the focal plane of the collimating mirror, this region is large enough for some of the doubly diffracted energy to spill out the exit slit as false energy. To avoid this we mask a horizontal strip of the grating somewhat wider than the slit height when maximum radiation purity is required. This difficulty could be avoided by using an optical system2 in which the entrance and exit slits are widely separated, at the cost of an increase in the over-all size of the instrument, and some impairment of its performance as a lamellar grating interferometer.
  21. P. L. Richards, Phys. Rev. Letters 7, 412 (1961).
    [CrossRef]
  22. J. Strong and G. A. Vanasse, J. Phys. Radium 19, 192 (1958).
    [CrossRef]
  23. J. Strong and G. A. Vanasse, J. Opt. Soc. Am. 50, 113 (1960).
    [CrossRef]
  24. See, for example, H. H. Skilling, Fundamentals of Electric Waves (John Wiley & Sons, Inc., New York, 1948), p. 204.
  25. H. A. Gebbie, 1959 Symposium on Interferometry, Teddington, England (unpublished).
  26. K. D. Möller and R. V. McKnight, J. Opt. Soc. Am. 53, 760 (1963).
    [CrossRef]
  27. R. F. Renk and L. Genzel, Appl. Opt. 1, 643 (1962).
    [CrossRef]
  28. L. Genzel (private communication).
  29. P. F. Parshin, Opt. i Spektroskopiya 13, 740 (1962)[English transl.: Opt. Spectry. 13, 418 (1962)].
  30. G. A. Vanasse, J. Opt. Soc. Am. 52, 472 (1962).
    [CrossRef]
  31. E. V. Loewenstein, Appl. Opt. 2, 491 (1963).
    [CrossRef]
  32. D. W. Williamson, J. Opt. Soc. Am. 42, 712 (1952).
    [CrossRef]
  33. P. L. Richards, J. Appl. Phys. 34, 1237 (1963);J. Appl. Phys. 35, 850 (1964).
    [CrossRef]
  34. W. S. Boyle and K. F. Rodgers, J. Opt. Soc. Am. 49, 66 (1959).
    [CrossRef]
  35. J. E. Kunzler, T. H. Geballe, and G. W. Hull, Rev. Sci. Instr. 28, 96 (1957).
    [CrossRef]
  36. F. J. Low, J. Opt. Soc. Am. 51, 1300 (1961).
    [CrossRef]
  37. J. Connes6 has made some comparisons with grating spectrometers in the near-infrared on weak source experiments.
  38. N. G. Yaroslavski and A. E. Stanevich, Opt. i Spektroskopiya 5, 384 (1958);Opt. i Spektroskopiya 7, 626 (1959).[English transl.: Opt. Spectry. 7, 380 (1959)].
  39. E. Archbold and H. A. Gebbie, Proc. Phys. Soc. (London) 80, 793 (1962).
    [CrossRef]
  40. H. A. Gebbie, K. J. Habell, and S. P. Middleton, Proceedings of the Conference on Optical Instruments and Techniques (Chapman and Hall, Ltd., London, 1962), p. 43.
  41. P. F. Parshin, Opt. i Spektroskopiya 14, 388 (1963)[English transl.: Opt. Spectry. 14, 207 (1963)].
  42. E. H. Putley, J. Phys. Chem. Solids 22, 241 (1961).
    [CrossRef]
  43. D. W. Goodwin and R. H. Jones, J. Appl. Phys. 32, 2056 (1961).
    [CrossRef]
  44. M. A. C. S. Brown and M. F. Kimmitt, Brit. Commun. Electron. 11, 608 (1963).

1963 (5)

P. L. Richards, J. Appl. Phys. 34, 1237 (1963);J. Appl. Phys. 35, 850 (1964).
[CrossRef]

P. F. Parshin, Opt. i Spektroskopiya 14, 388 (1963)[English transl.: Opt. Spectry. 14, 207 (1963)].

M. A. C. S. Brown and M. F. Kimmitt, Brit. Commun. Electron. 11, 608 (1963).

E. V. Loewenstein, Appl. Opt. 2, 491 (1963).
[CrossRef]

K. D. Möller and R. V. McKnight, J. Opt. Soc. Am. 53, 760 (1963).
[CrossRef]

1962 (4)

G. A. Vanasse, J. Opt. Soc. Am. 52, 472 (1962).
[CrossRef]

R. F. Renk and L. Genzel, Appl. Opt. 1, 643 (1962).
[CrossRef]

P. F. Parshin, Opt. i Spektroskopiya 13, 740 (1962)[English transl.: Opt. Spectry. 13, 418 (1962)].

E. Archbold and H. A. Gebbie, Proc. Phys. Soc. (London) 80, 793 (1962).
[CrossRef]

1961 (6)

E. H. Putley, J. Phys. Chem. Solids 22, 241 (1961).
[CrossRef]

D. W. Goodwin and R. H. Jones, J. Appl. Phys. 32, 2056 (1961).
[CrossRef]

P. L. Richards, Phys. Rev. Letters 7, 412 (1961).
[CrossRef]

J. Connes, Rev. Opt. 40, 45, 116, 171, and 231 (1961).

A. S. Barker and M. Tinkham, Bull. Am. Phys. Soc. 6, 112 (1961).

F. J. Low, J. Opt. Soc. Am. 51, 1300 (1961).
[CrossRef]

1960 (3)

J. Strong and G. A. Vanasse, J. Opt. Soc. Am. 50, 113 (1960).
[CrossRef]

P. Jacquinot, Rept. Progr. Phys. 23, 267 (1960).
[CrossRef]

L. Genzel, J. Mol. Spectry. 4, 241 (1960).
[CrossRef]

1959 (3)

1958 (5)

R. C. Ohlman, P. L. Richards, and M. Tinkham, J. Opt. Soc. Am. 48, 531 (1958).
[CrossRef]

For example, see H. Yoshinaga and et al., J. Opt. Soc. Am. 48, 315 (1958);D. Bloor and et al., Proc. Roy. Soc. (London) A260, 510 (1961);V. N. Murzin and A. I. Demshina, Opt. i Spektro-skopiya 13, 826 (1962)[English transl.: Opt. Spectry. 13, 467 (1963)].
[CrossRef]

P. Fellgett, J. Phys. Radium 19, 187, 237 (1958).
[CrossRef]

J. Strong and G. A. Vanasse, J. Phys. Radium 19, 192 (1958).
[CrossRef]

N. G. Yaroslavski and A. E. Stanevich, Opt. i Spektroskopiya 5, 384 (1958);Opt. i Spektroskopiya 7, 626 (1959).[English transl.: Opt. Spectry. 7, 380 (1959)].

1957 (3)

L. Genzel and R. Weber, Z. Angew. Phys. 10, 127 (1957);Z. Angew. Phys. 10, 195 (1958).

For a discussion of the early development of Fourier transform spectroscopy, see J. Strong, J. Opt. Soc. Am. 47, 354 (1957).
[CrossRef]

J. E. Kunzler, T. H. Geballe, and G. W. Hull, Rev. Sci. Instr. 28, 96 (1957).
[CrossRef]

1956 (1)

H. A. Gebbie and G. A. Vanasse, Nature 178, 432 (1956).
[CrossRef]

1954 (1)

1952 (2)

Archbold, E.

E. Archbold and H. A. Gebbie, Proc. Phys. Soc. (London) 80, 793 (1962).
[CrossRef]

Barker, A. S.

A. S. Barker and M. Tinkham, Bull. Am. Phys. Soc. 6, 112 (1961).

Bell, E. E.

E. E. Bell (private communication).

Boyle, W. S.

Brown, M. A. C. S.

M. A. C. S. Brown and M. F. Kimmitt, Brit. Commun. Electron. 11, 608 (1963).

Budenstein, P. P.

See, for example, R. S. Ohl, P. P. Budenstein, and C. A. Burrus, Rev. Sci. Instr. 30, 765 (1959).
[CrossRef]

Burrus, C. A.

See, for example, R. S. Ohl, P. P. Budenstein, and C. A. Burrus, Rev. Sci. Instr. 30, 765 (1959).
[CrossRef]

Connes, J.

J. Connes, Rev. Opt. 40, 45, 116, 171, and 231 (1961).

Fellgett, P.

P. Fellgett, J. Phys. Radium 19, 187, 237 (1958).
[CrossRef]

Geballe, T. H.

J. E. Kunzler, T. H. Geballe, and G. W. Hull, Rev. Sci. Instr. 28, 96 (1957).
[CrossRef]

Gebbie, H. A.

E. Archbold and H. A. Gebbie, Proc. Phys. Soc. (London) 80, 793 (1962).
[CrossRef]

H. A. Gebbie and G. A. Vanasse, Nature 178, 432 (1956).
[CrossRef]

H. A. Gebbie, K. J. Habell, and S. P. Middleton, Proceedings of the Conference on Optical Instruments and Techniques (Chapman and Hall, Ltd., London, 1962), p. 43.

H. A. Gebbie, 1959 Symposium on Interferometry, Teddington, England (unpublished).

Genzel, L.

R. F. Renk and L. Genzel, Appl. Opt. 1, 643 (1962).
[CrossRef]

L. Genzel, J. Mol. Spectry. 4, 241 (1960).
[CrossRef]

L. Genzel and R. Weber, Z. Angew. Phys. 10, 127 (1957);Z. Angew. Phys. 10, 195 (1958).

L. Genzel (private communication).

Goldman, S.

S. Goldman, Information Theory (Prentice-Hall, Inc., Engle-wood Cliffs, New Jersey, 1953), pp. 67 ff.

Goodwin, D. W.

D. W. Goodwin and R. H. Jones, J. Appl. Phys. 32, 2056 (1961).
[CrossRef]

Habell, K. J.

H. A. Gebbie, K. J. Habell, and S. P. Middleton, Proceedings of the Conference on Optical Instruments and Techniques (Chapman and Hall, Ltd., London, 1962), p. 43.

Hull, G. W.

J. E. Kunzler, T. H. Geballe, and G. W. Hull, Rev. Sci. Instr. 28, 96 (1957).
[CrossRef]

Jacquinot, P.

P. Jacquinot, Rept. Progr. Phys. 23, 267 (1960).
[CrossRef]

P. Jacquinot, J. Opt. Soc. Am. 44, 761 (1954).
[CrossRef]

Jones, R. H.

D. W. Goodwin and R. H. Jones, J. Appl. Phys. 32, 2056 (1961).
[CrossRef]

Kimmitt, M. F.

M. A. C. S. Brown and M. F. Kimmitt, Brit. Commun. Electron. 11, 608 (1963).

Kunzler, J. E.

J. E. Kunzler, T. H. Geballe, and G. W. Hull, Rev. Sci. Instr. 28, 96 (1957).
[CrossRef]

Loewenstein, E. V.

Low, F. J.

McCubbin, T. K.

McKnight, R. V.

Middleton, S. P.

H. A. Gebbie, K. J. Habell, and S. P. Middleton, Proceedings of the Conference on Optical Instruments and Techniques (Chapman and Hall, Ltd., London, 1962), p. 43.

Möller, K. D.

Ohl, R. S.

See, for example, R. S. Ohl, P. P. Budenstein, and C. A. Burrus, Rev. Sci. Instr. 30, 765 (1959).
[CrossRef]

Ohlman, R. C.

Parshin, P. F.

P. F. Parshin, Opt. i Spektroskopiya 14, 388 (1963)[English transl.: Opt. Spectry. 14, 207 (1963)].

P. F. Parshin, Opt. i Spektroskopiya 13, 740 (1962)[English transl.: Opt. Spectry. 13, 418 (1962)].

Putley, E. H.

E. H. Putley, J. Phys. Chem. Solids 22, 241 (1961).
[CrossRef]

Renk, R. F.

Richards, P. L.

P. L. Richards, J. Appl. Phys. 34, 1237 (1963);J. Appl. Phys. 35, 850 (1964).
[CrossRef]

P. L. Richards, Phys. Rev. Letters 7, 412 (1961).
[CrossRef]

R. C. Ohlman, P. L. Richards, and M. Tinkham, J. Opt. Soc. Am. 48, 531 (1958).
[CrossRef]

Rodgers, K. F.

Sinton, W. M.

Skilling, H. H.

See, for example, H. H. Skilling, Fundamentals of Electric Waves (John Wiley & Sons, Inc., New York, 1948), p. 204.

Stanevich, A. E.

N. G. Yaroslavski and A. E. Stanevich, Opt. i Spektroskopiya 5, 384 (1958);Opt. i Spektroskopiya 7, 626 (1959).[English transl.: Opt. Spectry. 7, 380 (1959)].

Strong, J.

Tinkham, M.

A. S. Barker and M. Tinkham, Bull. Am. Phys. Soc. 6, 112 (1961).

R. C. Ohlman, P. L. Richards, and M. Tinkham, J. Opt. Soc. Am. 48, 531 (1958).
[CrossRef]

Vanasse, G. A.

Weber, R.

L. Genzel and R. Weber, Z. Angew. Phys. 10, 127 (1957);Z. Angew. Phys. 10, 195 (1958).

Williamson, D. W.

Yaroslavski, N. G.

N. G. Yaroslavski and A. E. Stanevich, Opt. i Spektroskopiya 5, 384 (1958);Opt. i Spektroskopiya 7, 626 (1959).[English transl.: Opt. Spectry. 7, 380 (1959)].

Yoshinaga, H.

Appl. Opt. (2)

Brit. Commun. Electron. (1)

M. A. C. S. Brown and M. F. Kimmitt, Brit. Commun. Electron. 11, 608 (1963).

Bull. Am. Phys. Soc. (1)

A. S. Barker and M. Tinkham, Bull. Am. Phys. Soc. 6, 112 (1961).

J. Appl. Phys. (2)

P. L. Richards, J. Appl. Phys. 34, 1237 (1963);J. Appl. Phys. 35, 850 (1964).
[CrossRef]

D. W. Goodwin and R. H. Jones, J. Appl. Phys. 32, 2056 (1961).
[CrossRef]

J. Mol. Spectry. (1)

L. Genzel, J. Mol. Spectry. 4, 241 (1960).
[CrossRef]

J. Opt. Soc. Am. (12)

J. Phys. Chem. Solids (1)

E. H. Putley, J. Phys. Chem. Solids 22, 241 (1961).
[CrossRef]

J. Phys. Radium (2)

P. Fellgett, J. Phys. Radium 19, 187, 237 (1958).
[CrossRef]

J. Strong and G. A. Vanasse, J. Phys. Radium 19, 192 (1958).
[CrossRef]

Nature (1)

H. A. Gebbie and G. A. Vanasse, Nature 178, 432 (1956).
[CrossRef]

Opt. i Spektroskopiya (3)

P. F. Parshin, Opt. i Spektroskopiya 14, 388 (1963)[English transl.: Opt. Spectry. 14, 207 (1963)].

N. G. Yaroslavski and A. E. Stanevich, Opt. i Spektroskopiya 5, 384 (1958);Opt. i Spektroskopiya 7, 626 (1959).[English transl.: Opt. Spectry. 7, 380 (1959)].

P. F. Parshin, Opt. i Spektroskopiya 13, 740 (1962)[English transl.: Opt. Spectry. 13, 418 (1962)].

Phys. Rev. Letters (1)

P. L. Richards, Phys. Rev. Letters 7, 412 (1961).
[CrossRef]

Proc. Phys. Soc. (London) (1)

E. Archbold and H. A. Gebbie, Proc. Phys. Soc. (London) 80, 793 (1962).
[CrossRef]

Rept. Progr. Phys. (1)

P. Jacquinot, Rept. Progr. Phys. 23, 267 (1960).
[CrossRef]

Rev. Opt. (1)

J. Connes, Rev. Opt. 40, 45, 116, 171, and 231 (1961).

Rev. Sci. Instr. (2)

See, for example, R. S. Ohl, P. P. Budenstein, and C. A. Burrus, Rev. Sci. Instr. 30, 765 (1959).
[CrossRef]

J. E. Kunzler, T. H. Geballe, and G. W. Hull, Rev. Sci. Instr. 28, 96 (1957).
[CrossRef]

Z. Angew. Phys. (1)

L. Genzel and R. Weber, Z. Angew. Phys. 10, 127 (1957);Z. Angew. Phys. 10, 195 (1958).

Other (11)

J. Connes6 has made some comparisons with grating spectrometers in the near-infrared on weak source experiments.

H. A. Gebbie, K. J. Habell, and S. P. Middleton, Proceedings of the Conference on Optical Instruments and Techniques (Chapman and Hall, Ltd., London, 1962), p. 43.

The optical system used here can transmit false energy due to double diffraction. Energy at frequencies close to those which pass through the exit slit is roughly focused on the slit jaws or the face of the grating. Part of this energy finds its way back along the optical path, is diffracted by the grating, and irradiates a region around the entrance slit. Since the grating is not, in general, in the focal plane of the collimating mirror, this region is large enough for some of the doubly diffracted energy to spill out the exit slit as false energy. To avoid this we mask a horizontal strip of the grating somewhat wider than the slit height when maximum radiation purity is required. This difficulty could be avoided by using an optical system2 in which the entrance and exit slits are widely separated, at the cost of an increase in the over-all size of the instrument, and some impairment of its performance as a lamellar grating interferometer.

S. Goldman, Information Theory (Prentice-Hall, Inc., Engle-wood Cliffs, New Jersey, 1953), pp. 67 ff.

See, for example, H. H. Skilling, Fundamentals of Electric Waves (John Wiley & Sons, Inc., New York, 1948), p. 204.

H. A. Gebbie, 1959 Symposium on Interferometry, Teddington, England (unpublished).

L. Genzel (private communication).

For an interferometer whose limiting aperture subtends a solid angle Ω=πθ2 at a collimating mirror, the axial ray through the interferometer has a path difference cosθ∼1−Ω/2π times that of an extremal off-axis ray. This spread in values, δΔ/Δ, of path difference corresponds to a spread in frequency of δν/ν=δΔ/Δ =Ω/2π, thus limiting the resolving power to values less than R=ν/δν=2π/Ω. Another effect of the finite aperture is that the mean path difference for all rays entering the interferometer is 〈cosθ〉=(1−Ω/4π) times that of an axial ray. Thus, if the axial path difference is used in Eq. (3), the frequencies of spectral elements are overestimated by the factor 1+Ω/4π. For the interferometers described in Secs. III and IV, Ω=4.5×10−4 and 1.8×10−3 sr, respectively. The limitation on resolution is negligible for frequencies below 1000 cm−1, but significant frequency corrections must be made for high-resolution spectra at much lower frequencies.

Assuming otherwise comparable efficiency for the monochromator and interferometer.

E. E. Bell (private communication).

Block Associates, Inc., Cambridge 39, Massachusetts.

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Figures (9)

F. 1
F. 1

Diffraction grating monochromator described in Sec. II.

F. 2
F. 2

Lamellar grating interferometer described in Sec. III.

F. 3
F. 3

Comparison of beamsplitting efficiencies for the lamellar grating interferometer described in Sec. II, the Michelson interferometer described in Sec. II with a 3-mil Mylar beamsplitter, and the Michelson interferometer with a ∼250-lines/cm wire grid beamsplitter. The frequency at which cancellation begins to occur in the lamellar grating interferometer, and the frequency at which the wavelength equals the grating constant of the wire grid are marked as νc and 1/d, respectively. These curves give the relative efficiencies of the different instruments assuming the vignetting and reflection losses to be similar.

F. 4
F. 4

Michelson interferometer described in Sec. IV.

F. 5
F. 5

Block diagram of the interferometric spectrometer including cryostat for measuring transmission at low temperatures.

F. 6
F. 6

Examples of interferograms measured with the Michelson interferometer for various types of spectra. Curve (a) is the interferogram of the mercury lamp modified by filters which cut the spectrum off at 100 cm−1. Unnecessary interference effects such as channel spectra, which would show up as structure on this curve, were carefully eliminated. Curves (b) and (c) show interferograms for antiferromagnetic resonance in 1-mm-thick samples of FeF2 at 1.2°K. Curve (d) is an interferogram for H2O vapor.

F. 7
F. 7

Transmittance T and absorption coefficient −logT of a 1.5-m path of H2O vapor at a pressure of 20 Torr. measured using the Michelson. interferometer. The data shown here were obtained by drawing a smooth curve through the computed points which were at intervals of 0.1 cm−1. The measured frequencies should be reduced by 1.45×10−4ν to correct for the effects of finite instrumental aperture.8

F. 8
F. 8

Transmittance of a 1.5-m path of H2O vapor at a pressure of 2 Torr measured using tie Michelson interferometer. The measured frequencies should be reduced by 1.45×10−4ν to correct for the effects of finite instrumental aperture.8

F. 9
F. 9

Zero-field ferrimagnetic resonance in a 1-cm-thick powder sample of ytterbium iron garnet at 1.2°K, measured using the lamellar grating interferometer. Frequency corrections due to finite instrumental aperture are negligible here, but a reduction of 2.17 10−4ν must be made because of the separation of the entrance and exit slits of the lamellar grating interferometer.

Tables (3)

Tables Icon

Table I Grating space d and blaze angle θ for diffraction gratings and filter gratings, and carborundum mesh used to grind aluminum scatter plates.

Tables Icon

Table II Thickness of transmission filters. The filters are wedge shaped to reduce interference effects.

Tables Icon

Table III Measured transmittance of 1.1-cm i.d., 91-cm-long light pipes, and polished brass condenser cones, at frequencies of 20 and 100 cm−1.

Equations (6)

Equations on this page are rendered with MathJax. Learn more.

I ( Δ ) = S 0 ( 1 + cos 2 π ν Δ ) ,
I ( Δ ) = 0 S ( ν ) [ 1 + cos 2 π ν Δ ] d ν = 1 2 I ( 0 ) + 0 S ( ν ) cos 2 π ν Δ d ν ,
S ( ν ) = 4 0 [ I ( Δ ) 1 2 I ( 0 ) ] cos 2 π ν Δ d Δ ,
2 n ν max ν and 2 ( n 1 ) ν max + ν , where n = 1 , 2 , 3 , .
S 1 ( ν m ) = F 0 + 2 n = 1 n = N F n cos ( n m π N ) ,
S 2 ( ν m ) = F 0 + 2 n = 1 n = N ( 1 n N ) F n cos ( n m π N ) ,