Abstract

A high-efficiency extreme ultraviolet (EUV) imaging spectrometer has been constructed and tested. The spectrometer employs a concave toroidal grating illuminated at normal incidence in a Rowland circle mounting and has only one reflecting surface. The toroidal grating has been fabricated by a new technique employing an elastically deformable submaster grating which is replicated in a spherical form and then mechanically distorted to produce the desired aspect ratio of the toroidal surface for stigmatic imaging over the selected wavelength range. The fixed toroidal grating used in the spectrometer is then replicated from this surface. Photographic tests and initial photoelectric tests with a 2-D pulse-counting detector system have verified the image quality of the toroidal grating at wavelengths near 600 Å. The results of these initial tests are described in detail, and the basic designs of two instruments which could employ the imaging spectrometer for astrophysical investigations in space are briefly described, namely, a high-resolution EUV spectroheliometer for studies of the solar chromosphere, transition region, and corona and an EUV spectroscopic telescope for studies of nonsolar objects.

© 1988 Optical Society of America

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References

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  1. M. C. E. Huber, G. Tondello, “Stigmatic Performance of an EUV Spectrograph with a Single Toroidal Grating,” Appl. Opt. 18, 3948 (1979).
    [CrossRef] [PubMed]
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    [CrossRef]
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    [CrossRef] [PubMed]
  4. G. Lemaitre, “Coma and Astigmatism Compensated by Elastic Relaxation on Each Mirror Pair of a Two-Mosaic Telescope,” in Optical Telescopes of the Future, F. Pacini, W. Richter, R. N. Wilson, Eds. (European Southern Observatory, Garching bei munchen, 1978), p. 321.
  5. M. C. E. Huber, E. Jannitti, G. Lemaitre, G. Tondello, “Toroidal Grating Obtained on an Elastic Substrate,” Appl. Opt. 20, 2139 (1981).
    [CrossRef] [PubMed]
  6. Hyperfine, Inc., 4946 North 63rd St., Boulder, CO 80301, (303) 530-0709.
  7. M. Born, E. Wolf, Principles of Optics (Pergamon, New York, 1980), p. 303.
  8. M. Françon, Optical Interferometry (Academic, New York, 1966), p. 202.
  9. S. Johansson, U. Litzen, “Analysis of 4d–4f Transitions in Fe ii,” Phys. Scr. 10, 121 (1974).
    [CrossRef]
  10. W. M. Burton, B. A. Powell, “Fluorescence of Tetraphenyl-Butadiene in the Vacuum Ultraviolet,” Appl. Opt. 12, 87 (1973).
    [CrossRef] [PubMed]
  11. J. G. Timothy, “Multi-Anode Microchannel Array Detector Systems: Performance Characteristics,” Opt. Eng. 24, 1066 (1985).
    [CrossRef]
  12. J. G. Timothy, “Imaging at Soft X-Ray Wavelengths with High-Gain Microchannel Plate Detector Systems,” Proc. Soc. Photo-Opt. Instrum. Eng. 691, 35 (1986).

1986

J. G. Timothy, “Imaging at Soft X-Ray Wavelengths with High-Gain Microchannel Plate Detector Systems,” Proc. Soc. Photo-Opt. Instrum. Eng. 691, 35 (1986).

1985

J. G. Timothy, “Multi-Anode Microchannel Array Detector Systems: Performance Characteristics,” Opt. Eng. 24, 1066 (1985).
[CrossRef]

1984

1981

1979

1974

S. Johansson, U. Litzen, “Analysis of 4d–4f Transitions in Fe ii,” Phys. Scr. 10, 121 (1974).
[CrossRef]

1973

1950

Born, M.

M. Born, E. Wolf, Principles of Optics (Pergamon, New York, 1980), p. 303.

Burton, W. M.

Cash, W. C.

Françon, M.

M. Françon, Optical Interferometry (Academic, New York, 1966), p. 202.

Haber, H.

Huber, M. C. E.

Jannitti, E.

Johansson, S.

S. Johansson, U. Litzen, “Analysis of 4d–4f Transitions in Fe ii,” Phys. Scr. 10, 121 (1974).
[CrossRef]

Lemaitre, G.

M. C. E. Huber, E. Jannitti, G. Lemaitre, G. Tondello, “Toroidal Grating Obtained on an Elastic Substrate,” Appl. Opt. 20, 2139 (1981).
[CrossRef] [PubMed]

G. Lemaitre, “Coma and Astigmatism Compensated by Elastic Relaxation on Each Mirror Pair of a Two-Mosaic Telescope,” in Optical Telescopes of the Future, F. Pacini, W. Richter, R. N. Wilson, Eds. (European Southern Observatory, Garching bei munchen, 1978), p. 321.

Litzen, U.

S. Johansson, U. Litzen, “Analysis of 4d–4f Transitions in Fe ii,” Phys. Scr. 10, 121 (1974).
[CrossRef]

Powell, B. A.

Timothy, J. G.

J. G. Timothy, “Imaging at Soft X-Ray Wavelengths with High-Gain Microchannel Plate Detector Systems,” Proc. Soc. Photo-Opt. Instrum. Eng. 691, 35 (1986).

J. G. Timothy, “Multi-Anode Microchannel Array Detector Systems: Performance Characteristics,” Opt. Eng. 24, 1066 (1985).
[CrossRef]

Tondello, G.

Wolf, E.

M. Born, E. Wolf, Principles of Optics (Pergamon, New York, 1980), p. 303.

Appl. Opt.

J. Opt. Soc. Am.

Opt. Eng.

J. G. Timothy, “Multi-Anode Microchannel Array Detector Systems: Performance Characteristics,” Opt. Eng. 24, 1066 (1985).
[CrossRef]

Phys. Scr.

S. Johansson, U. Litzen, “Analysis of 4d–4f Transitions in Fe ii,” Phys. Scr. 10, 121 (1974).
[CrossRef]

Proc. Soc. Photo-Opt. Instrum. Eng.

J. G. Timothy, “Imaging at Soft X-Ray Wavelengths with High-Gain Microchannel Plate Detector Systems,” Proc. Soc. Photo-Opt. Instrum. Eng. 691, 35 (1986).

Other

G. Lemaitre, “Coma and Astigmatism Compensated by Elastic Relaxation on Each Mirror Pair of a Two-Mosaic Telescope,” in Optical Telescopes of the Future, F. Pacini, W. Richter, R. N. Wilson, Eds. (European Southern Observatory, Garching bei munchen, 1978), p. 321.

Hyperfine, Inc., 4946 North 63rd St., Boulder, CO 80301, (303) 530-0709.

M. Born, E. Wolf, Principles of Optics (Pergamon, New York, 1980), p. 303.

M. Françon, Optical Interferometry (Academic, New York, 1966), p. 202.

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Figures (13)

Fig. 1
Fig. 1

(a) Schematic of the imaging EUV spectrometer employing a single toroidal grating. Exact stigmatic focusing is obtained at angles of diffraction ±β0, which are defined by Eq. (1). Given a sufficiently small value of β0 and some depth of focus, effective stigmatic focusing can be achieved between and somewhat beyond the two stigmatic points. (b) Isometric display of the imaging properties at the two stigmatic points ±β0.

Fig. 2
Fig. 2

Schematics of telescope and imaging spectrometer systems: (a) high-resolution EUV spectroheliometer using a Gregorian telescope; (b) grazing-incidence telescope and normal-incidence spectrograph combination for astrophysical studies at wavelengths below 1200 Å.

Fig. 3
Fig. 3

(a) 3600 grooves mm−1 grating replicated on an elastically deformable substrate; (b) close-up showing the deforming actuator (a differential micrometer).

Fig. 4
Fig. 4

Form of the elastically deformable substrate. Forces are applied at the indicated points.

Fig. 5
Fig. 5

(a) Schematic of the modified Martin-Watt-Weinstein interferometer for the determination of the aspect ratio of the toroidal grating surface. (b) Schematic showing the zeroth-order technique for measurement of the aspect ratio of the toroidal grating surface.

Fig. 6
Fig. 6

Saddle fringe pattern produced by toroidal grating 3: (a) before thermal vacuum test; (b) after thermal vacuum test.

Fig. 7
Fig. 7

(a) Spectral images of ten pinholes arranged along the spectrometer entrance slit illuminated by a low-voltage low-pressure spark source. The arrows indicate the stigmatic wavelengths. (b) Spatial blur dimensions (with estimated uncertainties) as determined from the photographic spectra, shown in comparison with the ray-tracing results.

Fig. 8
Fig. 8

(a) Schematic of the optical system for the initial photoelectric tests of the toroidal grating. (b) Detail of the reimaging system and detector assembly.

Fig. 9
Fig. 9

(256 × 1024)-pixel MAMA detector system: (a) schematic of detector tube; (b) detector head assembly.

Fig. 10
Fig. 10

One-dimensional image at the wavelength of the He I resonance line at 584 Å of ten pinholes located along the spectrometer entrance slit. The different pinhole diameters (ranging from 10 to 33 μm) result in different peak intensities.

Fig. 11
Fig. 11

(a) Comparison of the pinhole and phosphor image profile with the image from the complete optical system including the diffraction grating. Solid line, pinhole and phosphor profile; dashed line, profile recorded with the toroidal grating. (b) Comparison of convolved pinhole image with the image from the toroidal grating.

Fig. 12
Fig. 12

Spectral images of the ten pinholes showing the self-reversal of the He I 584-Å resonance line with different gas pressures in the light source. Left, low gas pressure; right, high gas pressure. Good imaging is achieved although the line of pinholes is skew with respect to the normal to the plane of dispersion.

Fig. 13
Fig. 13

Spectral images from one pinhole showing the width and depth of the self-reversal of the He I 584-Å resonance line: (a) low gas pressure; (b) high gas pressure.

Tables (1)

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Table I Desired Characteristics of the Test Toroidal Diffraction Grating

Equations (5)

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R v = R h cos α cos β 0 .
Δ = h v - h h = a 2 2 ( 1 R v - 1 R h ) ~ a 2 2 R 2 ( R h - R v ) ,
R v R h = R - ( R h - R v 2 ) R + ( R h - R v 2 ) = 1 - R a Δ 1 + R a Δ = a - R Δ a + R Δ .
R v R h = cos α cos β 0 ,
R v R h = cos 2 γ .

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