Abstract

Seven plane gratings of high quality having ruled widths of more than 10 in. have now been produced on the M.I.T. servo controlled ruling engine, monitored with interference fringes. Resolving powers closely approaching the theoretical 900 000 in the 12th order green, and above 1 200 000 in the 26th order of 2537 A, have been obtained with several gratings in a 40-ft spectrograph having 10-in. concave mirrors. The wave fronts produced by the gratings, ruled with 7442 grooves per in. in some cases and 300 grooves per mm in others, have been studied with a large Michelson-Twyman interferometer at angles of incidence and reflection having sums up to 150°, in accordance with the method described by Stroke. Ghost and satellite intensities in all orders, as well as the blaze properties of the gratings, have been measured on a 5-m Littrow spectrograph with 8-in. lens. Rowland ghosts in several cases are found to be well below 0.1% in the 12th order green, and below one part in 100 000 at the angles at which ghost intensities are usually measured for purposes of comparison. In the better gratings satellite intensities total less than 1%, with no single satellite stronger than 0.3%. The stronger satellites reported in our previous 8-in. gratings were found to originate from tilting of the interferometer mirrors and the grating blank arising from variations along the ways. Since the gratings have 50 sq in. of ruled area and are well blazed they are extremely fast, 20 sec being adequate to give a satisfactory exposure to ordinary sources at dispersion of 12 mm per A. The blaze angle was varied from one grating to the next. Some of the gratings concentrate more than 50% of the incident green light in a single high order.

© 1959 Optical Society of America

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References

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  1. G. R. Harrison, J. Opt. Soc. Am. 39, 413 (1949).
    [Crossref]
  2. G. R. Harrison, Physics Today 3, 6 (1950).
    [Crossref]
  3. G. R. Harrison and J. E. Archer, J. Opt. Soc. Am. 41, 495 (1951).
    [Crossref]
  4. G. R. Harrison and G. W. Stroke, J. Opt. Soc. Am. 45, 112 (1955).
    [Crossref]
  5. Harrison, Sturgis, Baker, and Stroke, J. Opt. Soc. Am. 47, 15 (1957).
    [Crossref]
  6. Harrison, Sturgis, Davis, and Yamada, J. Opt. Soc. Am. 48, 287 (A) (1958).
  7. G. R. Harrison, Proc. Am. Phil. Soc. 102, 483 (1958).
  8. E. Ingelstam and E. Djurle, J. Opt. Soc. Am. 43, 572 (1953).
    [Crossref]
  9. G. W. Stroke [J. Opt. Soc. Am. 45, 30 (1955)] described the test instrument used in our laboratory, and developed the theory of the tests; W. E. Williams [Proc. Phys. Soc. (London) 45, 699 (1933)] used this device to test reflection echelons.
    [Crossref]
  10. W. F. Meggers and F. O. Westfall, Natl. Bur. Standards J. Research 44, 447 (1950).
    [Crossref]
  11. A. K. Pierce, J. Opt. Soc. Am. 47, 6 (1957).
    [Crossref]
  12. J. Strong, J. Opt. Soc. Am. 41, 3 (1951).
    [Crossref]
  13. H. D. Babcock and H. W. Babcock, J. Opt. Soc. Am. 41, 776 (1951).
    [Crossref]
  14. G. W. Stroke, private communication.

1958 (2)

Harrison, Sturgis, Davis, and Yamada, J. Opt. Soc. Am. 48, 287 (A) (1958).

G. R. Harrison, Proc. Am. Phil. Soc. 102, 483 (1958).

1957 (2)

1955 (2)

1953 (1)

1951 (3)

1950 (2)

G. R. Harrison, Physics Today 3, 6 (1950).
[Crossref]

W. F. Meggers and F. O. Westfall, Natl. Bur. Standards J. Research 44, 447 (1950).
[Crossref]

1949 (1)

Archer, J. E.

Babcock, H. D.

Babcock, H. W.

Baker,

Davis,

Harrison, Sturgis, Davis, and Yamada, J. Opt. Soc. Am. 48, 287 (A) (1958).

Djurle, E.

Harrison,

Harrison, Sturgis, Davis, and Yamada, J. Opt. Soc. Am. 48, 287 (A) (1958).

Harrison, Sturgis, Baker, and Stroke, J. Opt. Soc. Am. 47, 15 (1957).
[Crossref]

Harrison, G. R.

Ingelstam, E.

Meggers, W. F.

W. F. Meggers and F. O. Westfall, Natl. Bur. Standards J. Research 44, 447 (1950).
[Crossref]

Pierce, A. K.

Stroke,

Stroke, G. W.

Strong, J.

Sturgis,

Harrison, Sturgis, Davis, and Yamada, J. Opt. Soc. Am. 48, 287 (A) (1958).

Harrison, Sturgis, Baker, and Stroke, J. Opt. Soc. Am. 47, 15 (1957).
[Crossref]

Westfall, F. O.

W. F. Meggers and F. O. Westfall, Natl. Bur. Standards J. Research 44, 447 (1950).
[Crossref]

Yamada,

Harrison, Sturgis, Davis, and Yamada, J. Opt. Soc. Am. 48, 287 (A) (1958).

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Figures (10)

Fig. 1
Fig. 1

λ5461 A of natural mercury photographed in the 11th order of 10-in. grating No. 97 having 300 grooves/mm, showing resolution of 13 components. All lines marked with dots are real. Upper exposure: cooled electrodeless discharge; lower: ordinary cooled arc. Exposure times for both, about 60 sec.

Fig. 2
Fig. 2

Two exposures to Hg λ2537 A in the 24th order of grating No. 97. Upper: cooled electrodeless discharge; lower: warmer electrodeless discharge with self-reversal. Exposure times, about 60 sec. The entire width of the pattern is less than 1/20 A.

Fig. 3
Fig. 3

Artificial doublets for resolving power tests of grating No. 97 in single pass. Separation set so that if doublets are resolved, the theoretical resolution of 840 000 is attained in the 11th order green of the grating.

Fig. 4
Fig. 4

Normal and overexposed spectra showing the faintness of Rowland ghosts even at high angles. Upper: 20 sec exposure to λ5461 of Hg in the 11th order of grating No. 97. Lower: 4000 sec exposure, in which the Rowland ghosts, indicated by white dots, appear as only a trace. Satellites in this grating are stronger than the Rowland ghosts.

Fig. 5
Fig. 5

Photoelectric trace of background intensity in the neighborhood of λ5461 of Hg 198, showing the intensities of ghosts and satellites in the 11th order of grating No. 97. Some of the background irregularities are caused by a small percentage of natural mercury in the Hg 198 lamp.

Fig. 6
Fig. 6

View of the two control interferometers in place on the ruling engine. A, entrance lens for translation control interferometer; B, same for rotation control; M1, fixed mirror for both interferometers; M2, carriage-position mirror for both; G, 10-in. grating blank in half-ruled position; D, monorail track of diamond carriage; E, equalizer to reduce vertical motion of carriage arising from varying ball diameters.

Fig. 7
Fig. 7

Geometry of servo control of the grating carriage, showing measures taken to give translation control, rotation control, and minimization of the effects of tilt and twist.

Fig. 8
Fig. 8

Geometry of the effect of tilt which gives a displacement of the diamond ruling position relative to the front face of the control interferometer when the two are not at the same elevation about the axis of rotation.

Fig. 9
Fig. 9

View of the anteroom from which the engine is controlled during ruling. L, case containing Meggers Hg 198 lamp from which three control beams are taken; P, rotating polaroid to indicate diamond position; M, 75-megacycle oscillator for lamp excitation; O, oscilloscope for observing translation and rotation controls; D, drive motor; C, barometric pressure-variation correction cam; B, barometric correction servo; I, integrator for producing small variations in groove spacing; W, window through which engine can be observed under red light while operating.

Fig. 10
Fig. 10

Short sections of rotation correction charts recorded on the same parts of the screw during ruling of three successive gratings. The 2-mm period of the screw of up to five fringes amplitude makes necessary a rotation correction of about 1 4 fringe amplitude in this region. While the three curves are somewhat similar they differ sufficiently in detail to make predetermined cam correction impossible.