Abstract

A high resolution near ir Fourier spectrometer with the same general design as previously described laboratory instruments has been built for astronomical observations at a coudé focus. Present spectral range is 0.8–3.5 μm with PbS and Ge detectors and maximum path difference 1 m. The servo system can accommodate various recording modes: stepping or continuous scan, path difference modulation, sky chopping. A real time computer is incorporated into the system, which has been set up at the Hale 500-cm telescope on Mount Palomar. Samples of the results are given.

© 1975 Optical Society of America

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References

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  1. J. Connes, P. Connes, J. Opt. Soc. Am. 56, 896 (1966).
    [CrossRef]
  2. J. Connes, P. Connes, J. P. Maillard, J. Phys 28C2, 136 (1967).
  3. P. Connes, Annu. Rev. Astron. Astrophys. 8, 209 (1970).
    [CrossRef]
  4. U. Fink, H. P. Larson, R. F. Poppen, Astrophys. J. 187, 407 (1974);and Astrophys. J. 171, 291 (1972).
    [CrossRef]
  5. J. Pinard, J. Phys. 28C2, 136 (1967);Ann. Phys. 4, 147 (1967).
  6. An astronomical interferometer comparable to our types I and II has been built independently by Beer et al.7 and has produced many astronomical results; latest reference is Ref. 8. An airborne version has been described by Schindler9 and used aboard the Concorde supersonic aircraft to record solar spectra.10 Another instrument has been built by Malbrouck (University of Liège) and set up at the Jungfraujoch Observatory, mostly for recording ir solar spectra. There is a 2-m path difference laboratory interferometer at Air Force Cambridge Research Laboratories (Pritchard, Sakai and Vanasse AFCRL Report TR-73-0223). Lastly, an astronomical interferometer has been built by Wayte for high resolution work in the visible with the Isaac Newton telescope in Herstmonceux. This brief review mentions only operating systems related to our own by similarity in type of construction and mode of operation.
  7. R. Beer, R. H. Norton, C. H. Seaman, Rev. Sci. Instrum. 42, 1393 (1971).
    [CrossRef]
  8. R. Beer, D. L. Lambert, C. Sneden, Publ. Astron. Soc. Pac. 86, 806 (1974).
    [CrossRef]
  9. R. A. Schindler, Appl. Opt. 9, 301 (1970).
    [CrossRef] [PubMed]
  10. C. B. Farmer, Can. J. Chem. 52, 544 (1974);Proc. CIAP Conf. (1974) (in print) (1971).
    [CrossRef]
  11. J. Connes, H. Delouis, P. Connes, G. Guelachvili, J. P. Maillard, G. Michel, Nouv. Rev. Opt. Appl. 1, 3 (1971).
    [CrossRef]
  12. G. Guelachvili, Nouv. Rev. Opt. Appl. 3, 317 (1972).
    [CrossRef]
  13. J. Connes, in Aspen International Conference in Fourier Spectroscopy, AFCRL Spec. Rep. 114 (1971), p. 83.
  14. H. Delouis, in Aspen Int. Conf. on Fourier Spectrosc., AFCRL Spec. Report 114 (1970), p. 145.
  15. G. Guelachvili, Opt. Commun. 8, 171 (1973).
    [CrossRef]
  16. C. Amiot, G. Guelachvili, J. Mol. Spectrosc. 51, 475 (1974).
    [CrossRef]
  17. E. Luc-Koenig, C. Morillon, J. Verges, Physica 70, 175 (1973).
    [CrossRef]
  18. J. P. Maillard, M. Combes, Th. Encrenaz, J. Lecacheux, Astron. Astrophys. 25, 219 (1973);Astron. Astrophys. 28, 457 (1973).
  19. P. Connes, G. Michel, in Aspen International Conference on Fourier Spectroscopy, AFCRL Spec. Rep. 114 (1971), p. 313.
  20. G. Michel, Appl. Opt. 11, 2671 (1972).
    [CrossRef] [PubMed]
  21. P. Connes, G. Michel, Astrophys. J. 190, L29 (1974).
    [CrossRef]
  22. W. H. Steel, Opt. Acta 21, 599 (1974).
    [CrossRef]
  23. RCA Corporation, Montreal, Canada.
  24. Interferometer V uses silicon detectors with builtin preamplifiers instead.
  25. M. Cuisenier, J. Pinard, J. Phys. 28C2, 97 (1967).
  26. W. H. Steel, Interferometry (Cambridge U.P., Cambridge, England, 1967), p. 84.
  27. The compensation process can equally well be understood in different terms. Each cat's eye is a point-symmetrical retroreflector, i.e., all rays are returned symmetrical with respect to a particular point of the axis: the image of the MF center of curvature given by ME. Varying the curvature of MF in the manner described above means keeping this center of symmetry stationary while the cat's eye moves. Then the two emerging rays originating from a given incoming ray are coincident, a necessary condition for field compensation.
  28. G. Lemaitre, Thèse, Faculte des Sciences de Marseille (1973).
  29. Two recent references on flexible mirrors are Refs. 30 and 31; in the second case the design is comparable to our own. No indication of actual accuracy is given.
  30. S. Mikoshiba, B. Ahlborn, Rev. Sci. Instrum. 44, 508 (1973).
    [CrossRef]
  31. E. Bin-nun, F. Dothan-Deutsch, Rev. Sci. Instrum. 44, 512 (1973).
    [CrossRef]
  32. T. J. Deeming, L. M. Trafton, Appl. Opt. 10, 382 (1971).
    [CrossRef] [PubMed]
  33. J. T. Trauger, F. L. Roesler, Appl. Opt. 11, 1964 (1972).
    [CrossRef] [PubMed]
  34. If field compensation is not available, one can nevertheless realize approximate compensation of planetary rotation by applying this same shear to the wavefronts. Monochromatic fringes within the planetary image diameter would then appear curved, and the situation would be generally similar to the Fabry Perot one.33
  35. Size and weight of the device tend to grow as the cube of the length; this is why a more complex, nonuniform field, switched current type was preferred for interferometers III A, B, C.11
  36. However, the RTC has also been used with a fast scanning interferometer at low resolution.20
  37. G. P. Kuiper, Commun. Lunar Planet. Lab. Univ. Ariz. 1, 83 (1962).

1974 (6)

U. Fink, H. P. Larson, R. F. Poppen, Astrophys. J. 187, 407 (1974);and Astrophys. J. 171, 291 (1972).
[CrossRef]

R. Beer, D. L. Lambert, C. Sneden, Publ. Astron. Soc. Pac. 86, 806 (1974).
[CrossRef]

C. B. Farmer, Can. J. Chem. 52, 544 (1974);Proc. CIAP Conf. (1974) (in print) (1971).
[CrossRef]

C. Amiot, G. Guelachvili, J. Mol. Spectrosc. 51, 475 (1974).
[CrossRef]

P. Connes, G. Michel, Astrophys. J. 190, L29 (1974).
[CrossRef]

W. H. Steel, Opt. Acta 21, 599 (1974).
[CrossRef]

1973 (5)

G. Guelachvili, Opt. Commun. 8, 171 (1973).
[CrossRef]

S. Mikoshiba, B. Ahlborn, Rev. Sci. Instrum. 44, 508 (1973).
[CrossRef]

E. Bin-nun, F. Dothan-Deutsch, Rev. Sci. Instrum. 44, 512 (1973).
[CrossRef]

E. Luc-Koenig, C. Morillon, J. Verges, Physica 70, 175 (1973).
[CrossRef]

J. P. Maillard, M. Combes, Th. Encrenaz, J. Lecacheux, Astron. Astrophys. 25, 219 (1973);Astron. Astrophys. 28, 457 (1973).

1972 (3)

1971 (5)

T. J. Deeming, L. M. Trafton, Appl. Opt. 10, 382 (1971).
[CrossRef] [PubMed]

J. Connes, in Aspen International Conference in Fourier Spectroscopy, AFCRL Spec. Rep. 114 (1971), p. 83.

J. Connes, H. Delouis, P. Connes, G. Guelachvili, J. P. Maillard, G. Michel, Nouv. Rev. Opt. Appl. 1, 3 (1971).
[CrossRef]

P. Connes, G. Michel, in Aspen International Conference on Fourier Spectroscopy, AFCRL Spec. Rep. 114 (1971), p. 313.

R. Beer, R. H. Norton, C. H. Seaman, Rev. Sci. Instrum. 42, 1393 (1971).
[CrossRef]

1970 (3)

P. Connes, Annu. Rev. Astron. Astrophys. 8, 209 (1970).
[CrossRef]

R. A. Schindler, Appl. Opt. 9, 301 (1970).
[CrossRef] [PubMed]

H. Delouis, in Aspen Int. Conf. on Fourier Spectrosc., AFCRL Spec. Report 114 (1970), p. 145.

1967 (3)

J. Pinard, J. Phys. 28C2, 136 (1967);Ann. Phys. 4, 147 (1967).

J. Connes, P. Connes, J. P. Maillard, J. Phys 28C2, 136 (1967).

M. Cuisenier, J. Pinard, J. Phys. 28C2, 97 (1967).

1966 (1)

1962 (1)

G. P. Kuiper, Commun. Lunar Planet. Lab. Univ. Ariz. 1, 83 (1962).

Ahlborn, B.

S. Mikoshiba, B. Ahlborn, Rev. Sci. Instrum. 44, 508 (1973).
[CrossRef]

Amiot, C.

C. Amiot, G. Guelachvili, J. Mol. Spectrosc. 51, 475 (1974).
[CrossRef]

Beer, R.

R. Beer, D. L. Lambert, C. Sneden, Publ. Astron. Soc. Pac. 86, 806 (1974).
[CrossRef]

R. Beer, R. H. Norton, C. H. Seaman, Rev. Sci. Instrum. 42, 1393 (1971).
[CrossRef]

Bin-nun, E.

E. Bin-nun, F. Dothan-Deutsch, Rev. Sci. Instrum. 44, 512 (1973).
[CrossRef]

Combes, M.

J. P. Maillard, M. Combes, Th. Encrenaz, J. Lecacheux, Astron. Astrophys. 25, 219 (1973);Astron. Astrophys. 28, 457 (1973).

Connes, J.

J. Connes, in Aspen International Conference in Fourier Spectroscopy, AFCRL Spec. Rep. 114 (1971), p. 83.

J. Connes, H. Delouis, P. Connes, G. Guelachvili, J. P. Maillard, G. Michel, Nouv. Rev. Opt. Appl. 1, 3 (1971).
[CrossRef]

J. Connes, P. Connes, J. P. Maillard, J. Phys 28C2, 136 (1967).

J. Connes, P. Connes, J. Opt. Soc. Am. 56, 896 (1966).
[CrossRef]

Connes, P.

P. Connes, G. Michel, Astrophys. J. 190, L29 (1974).
[CrossRef]

J. Connes, H. Delouis, P. Connes, G. Guelachvili, J. P. Maillard, G. Michel, Nouv. Rev. Opt. Appl. 1, 3 (1971).
[CrossRef]

P. Connes, G. Michel, in Aspen International Conference on Fourier Spectroscopy, AFCRL Spec. Rep. 114 (1971), p. 313.

P. Connes, Annu. Rev. Astron. Astrophys. 8, 209 (1970).
[CrossRef]

J. Connes, P. Connes, J. P. Maillard, J. Phys 28C2, 136 (1967).

J. Connes, P. Connes, J. Opt. Soc. Am. 56, 896 (1966).
[CrossRef]

Cuisenier, M.

M. Cuisenier, J. Pinard, J. Phys. 28C2, 97 (1967).

Deeming, T. J.

Delouis, H.

J. Connes, H. Delouis, P. Connes, G. Guelachvili, J. P. Maillard, G. Michel, Nouv. Rev. Opt. Appl. 1, 3 (1971).
[CrossRef]

H. Delouis, in Aspen Int. Conf. on Fourier Spectrosc., AFCRL Spec. Report 114 (1970), p. 145.

Dothan-Deutsch, F.

E. Bin-nun, F. Dothan-Deutsch, Rev. Sci. Instrum. 44, 512 (1973).
[CrossRef]

Encrenaz, Th.

J. P. Maillard, M. Combes, Th. Encrenaz, J. Lecacheux, Astron. Astrophys. 25, 219 (1973);Astron. Astrophys. 28, 457 (1973).

Farmer, C. B.

C. B. Farmer, Can. J. Chem. 52, 544 (1974);Proc. CIAP Conf. (1974) (in print) (1971).
[CrossRef]

Fink, U.

U. Fink, H. P. Larson, R. F. Poppen, Astrophys. J. 187, 407 (1974);and Astrophys. J. 171, 291 (1972).
[CrossRef]

Guelachvili, G.

C. Amiot, G. Guelachvili, J. Mol. Spectrosc. 51, 475 (1974).
[CrossRef]

G. Guelachvili, Opt. Commun. 8, 171 (1973).
[CrossRef]

G. Guelachvili, Nouv. Rev. Opt. Appl. 3, 317 (1972).
[CrossRef]

J. Connes, H. Delouis, P. Connes, G. Guelachvili, J. P. Maillard, G. Michel, Nouv. Rev. Opt. Appl. 1, 3 (1971).
[CrossRef]

Kuiper, G. P.

G. P. Kuiper, Commun. Lunar Planet. Lab. Univ. Ariz. 1, 83 (1962).

Lambert, D. L.

R. Beer, D. L. Lambert, C. Sneden, Publ. Astron. Soc. Pac. 86, 806 (1974).
[CrossRef]

Larson, H. P.

U. Fink, H. P. Larson, R. F. Poppen, Astrophys. J. 187, 407 (1974);and Astrophys. J. 171, 291 (1972).
[CrossRef]

Lecacheux, J.

J. P. Maillard, M. Combes, Th. Encrenaz, J. Lecacheux, Astron. Astrophys. 25, 219 (1973);Astron. Astrophys. 28, 457 (1973).

Lemaitre, G.

G. Lemaitre, Thèse, Faculte des Sciences de Marseille (1973).

Luc-Koenig, E.

E. Luc-Koenig, C. Morillon, J. Verges, Physica 70, 175 (1973).
[CrossRef]

Maillard, J. P.

J. P. Maillard, M. Combes, Th. Encrenaz, J. Lecacheux, Astron. Astrophys. 25, 219 (1973);Astron. Astrophys. 28, 457 (1973).

J. Connes, H. Delouis, P. Connes, G. Guelachvili, J. P. Maillard, G. Michel, Nouv. Rev. Opt. Appl. 1, 3 (1971).
[CrossRef]

J. Connes, P. Connes, J. P. Maillard, J. Phys 28C2, 136 (1967).

Michel, G.

P. Connes, G. Michel, Astrophys. J. 190, L29 (1974).
[CrossRef]

G. Michel, Appl. Opt. 11, 2671 (1972).
[CrossRef] [PubMed]

J. Connes, H. Delouis, P. Connes, G. Guelachvili, J. P. Maillard, G. Michel, Nouv. Rev. Opt. Appl. 1, 3 (1971).
[CrossRef]

P. Connes, G. Michel, in Aspen International Conference on Fourier Spectroscopy, AFCRL Spec. Rep. 114 (1971), p. 313.

Mikoshiba, S.

S. Mikoshiba, B. Ahlborn, Rev. Sci. Instrum. 44, 508 (1973).
[CrossRef]

Morillon, C.

E. Luc-Koenig, C. Morillon, J. Verges, Physica 70, 175 (1973).
[CrossRef]

Norton, R. H.

R. Beer, R. H. Norton, C. H. Seaman, Rev. Sci. Instrum. 42, 1393 (1971).
[CrossRef]

Pinard, J.

J. Pinard, J. Phys. 28C2, 136 (1967);Ann. Phys. 4, 147 (1967).

M. Cuisenier, J. Pinard, J. Phys. 28C2, 97 (1967).

Poppen, R. F.

U. Fink, H. P. Larson, R. F. Poppen, Astrophys. J. 187, 407 (1974);and Astrophys. J. 171, 291 (1972).
[CrossRef]

Roesler, F. L.

Schindler, R. A.

Seaman, C. H.

R. Beer, R. H. Norton, C. H. Seaman, Rev. Sci. Instrum. 42, 1393 (1971).
[CrossRef]

Sneden, C.

R. Beer, D. L. Lambert, C. Sneden, Publ. Astron. Soc. Pac. 86, 806 (1974).
[CrossRef]

Steel, W. H.

W. H. Steel, Opt. Acta 21, 599 (1974).
[CrossRef]

W. H. Steel, Interferometry (Cambridge U.P., Cambridge, England, 1967), p. 84.

Trafton, L. M.

Trauger, J. T.

Verges, J.

E. Luc-Koenig, C. Morillon, J. Verges, Physica 70, 175 (1973).
[CrossRef]

Annu. Rev. Astron. Astrophys. (1)

P. Connes, Annu. Rev. Astron. Astrophys. 8, 209 (1970).
[CrossRef]

Appl. Opt. (4)

Aspen Int. Conf. on Fourier Spectrosc. (1)

H. Delouis, in Aspen Int. Conf. on Fourier Spectrosc., AFCRL Spec. Report 114 (1970), p. 145.

Aspen International Conference in Fourier Spectroscopy (1)

J. Connes, in Aspen International Conference in Fourier Spectroscopy, AFCRL Spec. Rep. 114 (1971), p. 83.

Aspen International Conference on Fourier Spectroscopy (1)

P. Connes, G. Michel, in Aspen International Conference on Fourier Spectroscopy, AFCRL Spec. Rep. 114 (1971), p. 313.

Astron. Astrophys. (1)

J. P. Maillard, M. Combes, Th. Encrenaz, J. Lecacheux, Astron. Astrophys. 25, 219 (1973);Astron. Astrophys. 28, 457 (1973).

Astrophys. J. (2)

P. Connes, G. Michel, Astrophys. J. 190, L29 (1974).
[CrossRef]

U. Fink, H. P. Larson, R. F. Poppen, Astrophys. J. 187, 407 (1974);and Astrophys. J. 171, 291 (1972).
[CrossRef]

Can. J. Chem. (1)

C. B. Farmer, Can. J. Chem. 52, 544 (1974);Proc. CIAP Conf. (1974) (in print) (1971).
[CrossRef]

Commun. Lunar Planet. Lab. Univ. Ariz. (1)

G. P. Kuiper, Commun. Lunar Planet. Lab. Univ. Ariz. 1, 83 (1962).

J. Mol. Spectrosc. (1)

C. Amiot, G. Guelachvili, J. Mol. Spectrosc. 51, 475 (1974).
[CrossRef]

J. Opt. Soc. Am. (1)

J. Phys (1)

J. Connes, P. Connes, J. P. Maillard, J. Phys 28C2, 136 (1967).

J. Phys. (2)

J. Pinard, J. Phys. 28C2, 136 (1967);Ann. Phys. 4, 147 (1967).

M. Cuisenier, J. Pinard, J. Phys. 28C2, 97 (1967).

Nouv. Rev. Opt. Appl. (2)

J. Connes, H. Delouis, P. Connes, G. Guelachvili, J. P. Maillard, G. Michel, Nouv. Rev. Opt. Appl. 1, 3 (1971).
[CrossRef]

G. Guelachvili, Nouv. Rev. Opt. Appl. 3, 317 (1972).
[CrossRef]

Opt. Acta (1)

W. H. Steel, Opt. Acta 21, 599 (1974).
[CrossRef]

Opt. Commun. (1)

G. Guelachvili, Opt. Commun. 8, 171 (1973).
[CrossRef]

Physica (1)

E. Luc-Koenig, C. Morillon, J. Verges, Physica 70, 175 (1973).
[CrossRef]

Publ. Astron. Soc. Pac. (1)

R. Beer, D. L. Lambert, C. Sneden, Publ. Astron. Soc. Pac. 86, 806 (1974).
[CrossRef]

Rev. Sci. Instrum. (3)

R. Beer, R. H. Norton, C. H. Seaman, Rev. Sci. Instrum. 42, 1393 (1971).
[CrossRef]

S. Mikoshiba, B. Ahlborn, Rev. Sci. Instrum. 44, 508 (1973).
[CrossRef]

E. Bin-nun, F. Dothan-Deutsch, Rev. Sci. Instrum. 44, 512 (1973).
[CrossRef]

Other (10)

If field compensation is not available, one can nevertheless realize approximate compensation of planetary rotation by applying this same shear to the wavefronts. Monochromatic fringes within the planetary image diameter would then appear curved, and the situation would be generally similar to the Fabry Perot one.33

Size and weight of the device tend to grow as the cube of the length; this is why a more complex, nonuniform field, switched current type was preferred for interferometers III A, B, C.11

However, the RTC has also been used with a fast scanning interferometer at low resolution.20

W. H. Steel, Interferometry (Cambridge U.P., Cambridge, England, 1967), p. 84.

The compensation process can equally well be understood in different terms. Each cat's eye is a point-symmetrical retroreflector, i.e., all rays are returned symmetrical with respect to a particular point of the axis: the image of the MF center of curvature given by ME. Varying the curvature of MF in the manner described above means keeping this center of symmetry stationary while the cat's eye moves. Then the two emerging rays originating from a given incoming ray are coincident, a necessary condition for field compensation.

G. Lemaitre, Thèse, Faculte des Sciences de Marseille (1973).

Two recent references on flexible mirrors are Refs. 30 and 31; in the second case the design is comparable to our own. No indication of actual accuracy is given.

An astronomical interferometer comparable to our types I and II has been built independently by Beer et al.7 and has produced many astronomical results; latest reference is Ref. 8. An airborne version has been described by Schindler9 and used aboard the Concorde supersonic aircraft to record solar spectra.10 Another instrument has been built by Malbrouck (University of Liège) and set up at the Jungfraujoch Observatory, mostly for recording ir solar spectra. There is a 2-m path difference laboratory interferometer at Air Force Cambridge Research Laboratories (Pritchard, Sakai and Vanasse AFCRL Report TR-73-0223). Lastly, an astronomical interferometer has been built by Wayte for high resolution work in the visible with the Isaac Newton telescope in Herstmonceux. This brief review mentions only operating systems related to our own by similarity in type of construction and mode of operation.

RCA Corporation, Montreal, Canada.

Interferometer V uses silicon detectors with builtin preamplifiers instead.

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Figures (23)

Fig. 1
Fig. 1

Astronomical light path. Four different levels are shown; output of each goes to input of next level. Each figure plane is horizontal.

Fig. 2
Fig. 2

Visible light path to finder eyepiece E and guiding photomultiplier PM (vertical plane).

Fig. 3
Fig. 3

Left: cross section of beam within interferometer. Projected light path of a principal ray is shown. Right: top view of beam splitter and beam mixer. Sideways displacement added for clarity.

Fig. 4
Fig. 4

Reference light path. Simplified diagram; actually the path is three dimensional, and the ingoing and outgoing rays pass through the centers of BM, BS, thus they should appear on top of each other.

Fig. 5
Fig. 5

Relay system used for Hale telescope (vertical plane). M3, M2 form a unit magnification system. LF is the field lens and window of Fig 1.

Fig. 6
Fig. 6

Guiding mirror MA. Tx,Ty: torque motors; Fx,Fy: magnesium alloy forks (not touching each other). X1, X2, Y1, Y2 magnesium alloy cubes fixed with epoxy to mirror back. Four flat springs S permit about 5° of rotation. On the right: guiding photomultiplier cathode and scan pattern for a centered star (giving zero demodulated output). Star follows ABCDEFGH path; actually distances such as HB, BD, etc. are zero. Half of the time is spent within the square aperature.

Fig. 7
Fig. 7

Guider performance. (a) Guiding mode. The residual error trace illustrates response to 20-Hz square wave perturbation. Transient error is corrected after 5 msec. (b) Slight cross coupling on perpendicular channel. (c) Chopping mode. The mirror is made to oscillate in X, and the beam goes from D1 to D2 (1 min of arc on the sky). (d) Cross coupling on Y channel. The small ripple is a residual from the 1-kHz carrier.

Fig. 8
Fig. 8

Deformation of flexible mirror shown with a simple Michelson interferometer at λ = 6328 Å: in the second arm a high accuracy concave, constant curvature (R = 740 mm) mirror is placed. Jupiter image diameter would be 10 mm.

Fig. 9
Fig. 9

Left: front view of planetary image projected onto small cat's eye mirror. Ox and Oy are directed along the equatorial and polar diameters, respectively. OX and OY are the lateral translation axes for the fixed cat's eye. Right: side view showing angle of tilt β.

Fig. 10
Fig. 10

Proposed control system for compensation of interferometer field and of planetary rotation.

Fig. 11
Fig. 11

General view of servo system. Operation of slave carriage involves a completely independent servo loop (upper left). The interferometric signal from the photomultipliers first produces a SSB modulated carrier (Fig. 13), then a dc error signal (Fig. 17), which is separated into high and low frequency components. These go to the servoing linear motor and piezoelectric ceramic. The HP and LP filters are actually complex, empirically adjusted phase correcting loops that incorporate signal differentiation for damping.

Fig. 12
Fig. 12

Slave carriage system. Top: horizontal view. RV: three vertical ball bearings. M: two magnets providing horizontal restoring force. B: two flexible belts pulling the carriage. Bottom: side view (linear and rotary motors omitted for clarity). F: four flexure hinges, each incorporating two pairs of crossed flat springs and giving a well defined rotation axis. Angle of tilt is greatly exaggerated compared to actual maximum.

Fig. 13
Fig. 13

Single sideband signal generation with two photomultipliers and high frequency path difference modulation.

Fig. 14
Fig. 14

Alternative scheme for single sideband signal generation involving three photomultipliers, dc amplification, and linear multipliers.

Fig. 15
Fig. 15

Digital programmable phase shifter with square wave output and manual analog phase shifter (similar to the hour angle phase shifter in Fig. 10).

Fig. 16
Fig. 16

Waveforms in digital phase shifter. (a) Master oscillator output at 1.2 MHz. (b) After clipping. (c) After differentiating. (d) Square wave output at 1.2 MHz/8 = 150 kHz when the plus gate is opened and minus is closed. (e) Increased frequency output if one minus pulse out of eight is added. (f) Reduced frequency if one plus pulse out of four is subtracted.

Fig. 17
Fig. 17

Direct current error signal generator (see text).

Fig. 18
Fig. 18

Upper. Waveforms as a function of time in dc error signal generation for N′ slightly greater than N. V is the direct voltage output of DA converter and simply reproduces the count difference, and VF is the filtered output. Lower: error signal VF, as a function of path difference error.

Fig. 19
Fig. 19

Servo performance as illustrated by the error signal. (a) Pure stepping at 1100 steps/sec; unfiltered DA converter output showing carrier residuals. Step size is λ0 = 0.6328 μm. (b) Stepping at 100 steps/sec with step size 30/8λ0 = 2.37 μm and modulating at 350 Hz with 15/8λ0 = 1.18-μm amplitude (i.e., maximum modulation efficiency at 4.75 μm in the recorded spectrum). Filtered DA output. Step transients indicated by arrows.

Fig. 20
Fig. 20

Recording system (simplified diagram).

Fig. 21
Fig. 21

Upper: N2O test spectrum (RTC output). 512,000 input samples; the full 4096-sample (4692–4772-cm−1) output is presented on two lines. Step size is 6/8λ0 = 0.47 μm and Δmax = 24 cm. Insert at right shows band head on an expanded scale. Complete 0–10.538-cm−1 range is available from magnetic tape recording and general purpose computer output. Center: Venus spectrum, 1048.000 samples, Δmax = 48 cm−1, 3-h recording time, PbS cells. A fraction of the RTC output is shown: Left, trace giving base line level and noise; right, 4658–4668-cm−1 range (1/1024 of total range) showing CO2 bands. Below: same, α Sco spectrum; broad modulations are due to stellar CO; sharp lines are telluric.

Fig. 22
Fig. 22

Low resolution Jupiter spectrum with Ge detector, through 5 sec of arc slit (about ⅛th of planetary light used), 4096 input samples, 5-cm−1 apodized resolution, 2-min recording time. Approximately half of 0–12,692-cm−1 RTC output is shown.

Fig. 23
Fig. 23

Improvements in the near ir Venus spectrum due to Fourier spectroscopy; same type detectors (cooled PbS) with almost the same NEP used throughout. Curve I by Kuiper,37 II from Ref. 1, III from Ref. 3, and IV (this work) by ourselves. Telescope sizes and resolving power gains are indicated; I, II, and III are discussed at greater length in Ref 3. Four strong CO2 Venusian bands are shown in I; the rotational structure is resolved in II; III shows lines from much weaker overlapping bands; IV gives a good approximation of the true line profile, together with ever fainter lines. Trace IV presents approximately 1/800th of the actual spectral range available from the magnetic tape—general purpose computer output (parts of which are obscured by H2O).

Equations (2)

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S 1 = π I sin 2 π σ 0 Δ M · sin ω t , S 1 = π I cos 2 π σ 0 Δ M · cos ω t ,
S = S 1 + S 2 = π I cos 2 π ( N 0 t σ 0 Δ M ) .

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