Abstract

A high efficiency spectrograph design for the EUV and soft x rays is presented. This grazing incidence system uses a plane surface reflection grating with rulings that are radial, like the spokes of a wheel. The grating is placed in a beam of light that is converging to a focus. The single reflection off the grating is in the conical diffraction mount ensuring maximum performance from the system. Aberrations and performance levels are discussed. The gratings can be manufactured with existing ruling engines. Sample applications to an x-ray monochromator and an EUV stellar spectrograph are discussed.

© 1983 Optical Society of America

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References

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1982 (5)

1981 (2)

1979 (2)

E. C. Bruner et al., Proc. Soc. Photo-Opt. Instrum. Eng. 184, 270 (1979).

P. Vincent, M. Neviere, D. Maystre, Appl. Opt. 18, 1780 (1979).
[CrossRef] [PubMed]

1978 (2)

1977 (1)

Barth, C. A.

Basri, G.

R. F. Malina, S. Bowyer, G. Basri, Astrophys. J. 262, 717 (1982).
[CrossRef]

Bowyer, S.

R. F. Malina, S. Bowyer, G. Basri, Astrophys. J. 262, 717 (1982).
[CrossRef]

Bruner, E. C.

E. C. Bruner et al., Proc. Soc. Photo-Opt. Instrum. Eng. 184, 270 (1979).

Caruso, A. J.

Cash, W.

Hunter, W. R.

Kohnert, R.

Lawrence, G. M.

Malina, R. F.

R. F. Malina, S. Bowyer, G. Basri, Astrophys. J. 262, 717 (1982).
[CrossRef]

Maystre, D.

McClintock, W.

W. McClintock, W. Cash, Proc. Soc. Photo-Opt. Instrum. Eng. 331, 321(1982).

McClintock, W. E.

Mount, G. H.

Neviere, M.

Steele, R. E.

Timothy, J. G.

Vincent, P.

Visser, H.

Werner, W.

Woodgate, B. E.

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Figures (9)

Fig. 1
Fig. 1

Side view of a converging beam reflected at grazing incidence off a plane grating shows that for the zero-order light the quantity L* sinγ is a constant equal to h, despite the variation in both L and γ.

Fig. 2
Fig. 2

Top view of a radial groove grating shows that the grooves converge to a hub which is off the edge of the grating.

Fig. 3
Fig. 3

Perspective view of a converging beam being diffracted by a radial groove grating. For good performance the zero-order focus is offset from the hub so that all rays satisfy the blaze constraint α = β.

Fig. 4
Fig. 4

Ray tracing of a radial groove spectrograph shows the layout of the focal plane. Wavelengths of light from 100 to 500 Å plus zero order demonstrate that the light falls on a semicircle.

Fig. 5
Fig. 5

These ray traces are of pairs of wavelengths of light separated by one part in 500. Note the resolution is independent of wavelength, but as the wavelength grows so does the astigmatism.

Fig. 6
Fig. 6

This drawing demonstrates the geometric orientation of the optimal focal plane for the radial groove spectrograph. The center of curvature (C) is halfway between the grating (G) and the ruling hub (H). The zero-order light focuses at 0, and the first-order light at 1. Note that, if the detector is oriented perpendicular to the incoming light, the optimal focal plane displacement goes negative before going strongly positive.

Fig. 7
Fig. 7

Schematic of an x-ray spectrograph. The light enters the spectrograph through a slit and is focused by a grazing incidence ellipsoidal mirror. The light in the focused beam is intercepted by a radial groove grating which disperses the light.

Fig. 8
Fig. 8

Spectrograph of Fig. 7 can be turned into a monochromator by rotating the grating about the direction of its central groove. This has the effect of keeping the radius of the cone of diffraction the same but changing the wavelength of the light leaving the slit. This figure is a schematic of the focal plane: the ellipsoid focuses at EF, the plane of the grating surface is defined by the solid, horizontal line. The zero-order light is thus to be found at F1; an exit slit lies somewhere else on the circle. If the grating is rotated so its plane lies along the dashed line, the zero order will move to F2, and a different wavelength will enter the slit.

Fig. 9
Fig. 9

One application of the radial groove concept is in stellar EUV spectroscopy. The collimated light from a star enters a grazing incidence telescope and is focused. A radial groove grating intercepts the light and disperses it onto a microchannel plate detector. A zero-order monitor gives pointing information, and an ultrathin filter is used to decrease the Lyman-α nightglow background.

Equations (10)

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n λ = d sin γ ( sin α + sin β ) .
sin β = n λ d L h .
sin β = n λ h θ L R = n λ h θ 1 cos γ .
Q X = d x x D + z l 2 n λ θ ,
Q Z = d z z D x l 2 n λ θ ,
Q Y = 1 Q X 2 Q Y 2 ,
D = [ ( d x x ) 2 + d y 2 + ( d z z ) 2 ] 1 / 2 ,
l 2 = x 2 + z 2 .
x = d x + n λ θ [ 1 + 0 ( x 2 / z 2 ) ] ,
R = 8 f 2 ,

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