Three types of new monochromators based on the new mounting of concave grating by Singh-Majumdar (SM) are described. These monochromators are very compact and simple in operation, fulfilling the requirements of a monochromator in a space telescope in the VUV region. It is found theoretically (by geometric optics theory of concave diffraction grating given by Beutler and modified by Namioka, and by a ray tracing procedure by drawing spot diagrams at different wavelengths) as well as experimentally in the laboratory by setting up the monochromator and taking sample spectra photographically that the spectral images have very little aberration as compared to other monochromators in the VUV region. The improvement obtained is three times.
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Δz′ = length of the spectral image; Δλ = breadth of the spectral image.
Table V
Characteristics of Different Monochromators Reproduced from Ref. 1
Kind of grating
ℛ
(100 − ξ)
f
η
Normal incidence
1-m spherical concave
0.8
100
8
10
In plane eagle
1-m spherical concave
0.8
100
6
13.3
Grazing incidence
2-m spherical concave
1
5.5
50
0.1
2-m ellipsoidal concave
1
30
30
1
Seya-Namioka
1-m spherical concave
0.83
40
12
2.8
1-m ellipsoidal concave
0.83
100
10
8.3
Ebert-Fastie
Plane
0.51
100
5
10.2
Table VI
Experimental Results Obtained from Iron Arc Spectra
λ(Å)
Δλ (cm) = breadth of the spectral lines
Δz′ = length of the spectral lines (cm)
Distance between vertical and horizontal images (cm) (a measure for astigmatism)
New mounting K = −0.5
Rowland circle mounting
New mounting K = −0.5
Rowland circle mounting
New mounting K = −0.5
Rowland circle mounting
α = 0
α = 5°
α = 10°
α = 0°
α = 0
α = 5°
α = 10°
α = 0°
α = 0
α = 5°
α = 10°
α = 0
4382
0.0400
0.0500
0.0576
0.0496
0.4
0.2
0.2
1.0
13.80
6.6
3
16.80
4404
0.0320
0.0450
0.0424
0.0400
4414
0.0320
0.0450
0.0368
0.0440
4422
0.0200
0.0280
0.0176
0.0192
4426
0.0240
0.0380
0.0224
0.0376
4430
0.0200
0.0300
0.0160
0.0280
4442
0.0320
0.0450
0.0280
0.0440
4447
0.0200
0.0370
0.0184
0.0360
4459
0.0216
0.0390
0.0200
0.0392
4461
0.0264
0.0380
0.0200
0.0384
4467
0.0240
0.0330
0.0176
0.0328
0.4
0.2
0.2
0.9
—
—
—
—
4469
0.0240
0.0250
0.0144
0.0240
4476
0.0216
0.0280
0.0168
0.0280
4482
0.0240
0.0340
0.0176
0.0320
4491
0.0240
0.0220
0.0136
0.0216
4495
0.0240
0.0300
0.0144
0.0304
4525
0.0240
0.0280
0.0104
0.0240
4528
0.0280
0.0320
0.0216
0.0416
0.4
0.2
0.2
0.9
14.40
7.5
3.8
18.3
4530
0.0240
0.0280
0.0112
0.0280
Note: The grating used is 8.5 × 4 cm2 in size, 5680 lines/cm, and with a radius of curvature of 3.048 m. The source slit dimension is 8 × 0.1 mm. Δz′ = length of the spectral image. Δλ = breadth of the spectral image.
Δz′ = length of the spectral image; Δλ = breadth of the spectral image.
Table V
Characteristics of Different Monochromators Reproduced from Ref. 1
Kind of grating
ℛ
(100 − ξ)
f
η
Normal incidence
1-m spherical concave
0.8
100
8
10
In plane eagle
1-m spherical concave
0.8
100
6
13.3
Grazing incidence
2-m spherical concave
1
5.5
50
0.1
2-m ellipsoidal concave
1
30
30
1
Seya-Namioka
1-m spherical concave
0.83
40
12
2.8
1-m ellipsoidal concave
0.83
100
10
8.3
Ebert-Fastie
Plane
0.51
100
5
10.2
Table VI
Experimental Results Obtained from Iron Arc Spectra
λ(Å)
Δλ (cm) = breadth of the spectral lines
Δz′ = length of the spectral lines (cm)
Distance between vertical and horizontal images (cm) (a measure for astigmatism)
New mounting K = −0.5
Rowland circle mounting
New mounting K = −0.5
Rowland circle mounting
New mounting K = −0.5
Rowland circle mounting
α = 0
α = 5°
α = 10°
α = 0°
α = 0
α = 5°
α = 10°
α = 0°
α = 0
α = 5°
α = 10°
α = 0
4382
0.0400
0.0500
0.0576
0.0496
0.4
0.2
0.2
1.0
13.80
6.6
3
16.80
4404
0.0320
0.0450
0.0424
0.0400
4414
0.0320
0.0450
0.0368
0.0440
4422
0.0200
0.0280
0.0176
0.0192
4426
0.0240
0.0380
0.0224
0.0376
4430
0.0200
0.0300
0.0160
0.0280
4442
0.0320
0.0450
0.0280
0.0440
4447
0.0200
0.0370
0.0184
0.0360
4459
0.0216
0.0390
0.0200
0.0392
4461
0.0264
0.0380
0.0200
0.0384
4467
0.0240
0.0330
0.0176
0.0328
0.4
0.2
0.2
0.9
—
—
—
—
4469
0.0240
0.0250
0.0144
0.0240
4476
0.0216
0.0280
0.0168
0.0280
4482
0.0240
0.0340
0.0176
0.0320
4491
0.0240
0.0220
0.0136
0.0216
4495
0.0240
0.0300
0.0144
0.0304
4525
0.0240
0.0280
0.0104
0.0240
4528
0.0280
0.0320
0.0216
0.0416
0.4
0.2
0.2
0.9
14.40
7.5
3.8
18.3
4530
0.0240
0.0280
0.0112
0.0280
Note: The grating used is 8.5 × 4 cm2 in size, 5680 lines/cm, and with a radius of curvature of 3.048 m. The source slit dimension is 8 × 0.1 mm. Δz′ = length of the spectral image. Δλ = breadth of the spectral image.
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