CH625055A5 - Annular optical device having a specific (unitary) power - Google Patents

Description

The present invention relates to an annular field optical device with unit power intended to form an image of a

3

625,055

Surface No of the object in the image

Radius (mm)

Distance to next surface

Materials

0

(plan)

144.92

Air

Object

1

-144.96

11.03

Fused silica

2

-151.75

88.70

Air

3

-957.30

16.75

Fused silica

4

-967.84

295.25

Air

5

-551.15

-279.07

Air

Mirror

6

-267.18

279.07

Air

Mirror

7

-551.15

-295.25

Air

Mirror

8

-967.84

-16.75

Fused silica

9

-957.30

-88.70

Air

10

-151.75

-11.03

Fused silica

11

-144.96

-144.92

Air

12

(plan)

Image and radius of the ring = 100 mm.

Ring radius = 100 mm.

Surface No of the object in the image

Radius (mm)

Distance to next surface

Materials

0

(plan)

107.13

Air

Object

1

-128.18

107.13

Fused silica

2

-135.29

378.48

Air

3

-541.32

-273.56

Air

Mirror

4

-264.61

273.56

Air

Mirror

5

-541.32

-590.28

Air

Mirror

6

-1772.58 *

-7.01

Fused silica

7

(plan)

-587.26

Air

8

541.32

273.56

Air

Mirror

9

264.61

-273.56

Air

Mirror

10

541.32

378.48

Air

Mirror

11

135.29

10.48

Fused silica

12

128.18

107.13

Air

13

(plan)

Picture

* Aspherical surface symmetrically arranged on the optical axis Deviation, X, with respect to the plane surface at distance r from the axis:

X = -1772.58-1 - ^ / 1772.58-r2 + 1.732xl0-8r4 + 4.210x10-

13r6

+ 8.278x10-I8r8-4.078xl0-21r10

Surface No

Radius (mm)

Distance to next surface

Materials

Note

0

(plan)

151.33

Air

Object

1

-726.89

28.69

Fused silica

2

-730.32

410.82

Air

3

-552.06

-280.16

Air

Mirror

4

-267.18

280.16

Air

Mirror

5

-552.06

-363.25

Air

Mirror

6

-160.78

-24.03

Fused silica

7

-145.19

-272.77

Air

8

145.19

-24.03

Fused silica

9

-160.78

-363.25

Air

10

552.06

280.16

Air

Mirror

11

267.18

-280.16

Air

Mirror

12

552.06

410.82

Air

Mirror

13

730.32

28.69

Fused silica

14

726.89

151.33

Air

15

(plan)

Picture

625,055

4

object with a magnification equal to unity, and in particular an optical device with wide spectral bands.

The optical device according to the invention is particularly suitable among other possible uses for carrying out the exposure of the photoresist layer (photoresist) coating the semiconductor grids during the manufacture of integrated circuits. A catadioptric system is already known which provides an image of an object with a high resolution coefficient, this image being reproduced in its finest details under a unit magnification, characterized in that it comprises convex and concave mirrors having their centers of curvature at the same point. The mirrors are arranged so as to produce at least three reflections in the system, they are used in the system with their conjugates on the axis at this point and to produce two conjugated zones with unit magnification arranged in a plane containing the centers of curvature , the axis of the system being normal to this plane and passing through this point. Although this system has many characteristics and advantages, the present invention relates to an improvement of this system. The desired results are obtained by the arrangements indicated in claim 1.

According to one embodiment, this device also comprises a chromatic compensation device which is arranged between the mirrors and the object and image positions, this device being for example constituted by a parallel flat plate normally mounted on the optical axis of the mirrors. Preferably, one of the faces of the parallel flat plate is aspherical, or the plate consists of a meniscus element mounted normally with respect to the optical axis of the mirrors.

According to another embodiment, the concave and convex mirrors are arranged so that their centers of curvature are separated by a distance at least approximately equal to 2% of the length of the shortest radius, these mirrors being placed in such a way we observe three reflections on the concave mirror and two reflections on the convex mirror. According to one embodiment, this optical system comprises a first half and a second half which each comprise a unit power optical system comprising an optical axis and having substantially normal conjugate planes with respect to this axis. The two halves are arranged coaxially back to back so that their overlapping planes are superimposed on at least one side of the optical system so as to form an intermediate image position, and arranged so as to produce object and image positions distinct from the other side of the optical system. In this embodiment, each half of the optical system comprises a meniscus element arranged symmetrically and substantially concentric, the convex radius of which is greater than the concave radius and the thickness of which is greater than the difference between the concave and convex rays, as well as at least a color correction element.

According to one embodiment, each optical system with unit power comprises a concave spherical mirror and a convex spherical mirror arranged opposite the concave mirror.

said mirrors being arranged so that their centers of curvature substantially coincide. Means are provided for defining a position for an object in such a way that its image is real in a second position, said convex mirror being arranged so as to reflect on the concave mirror the light coming from the object initially reflected towards the mirror. convex by the concave mirror, the light coming from the object being reflected at least twice on the concave mirror and at least once on the convex mirror before being focused in the image plane. The small aberrations which appear following a defect in the concentricity of the meniscus are compensated for by the introduction of a reduced defect in the concentricity of the pair of mirrors. That is to say, in each half of the optical system, the concave and convex mirrors are arranged in such a way that their centers of curvature are distant by a length less than 2% of the length of the shortest ray.

Preferably, the chromatic correction element is a parallel flat plate normally mounted on the optical axis of the mirrors. According to certain embodiments, the chromatic correction plate is mounted at the location of the intermediate image and in other embodiments it is mounted in each half of the system.

According to another embodiment of the system, the two halves of the optical system are arranged coaxially back to back so that the conjugate planes are superimposed on the two sides of the system so as to obtain an image position d on one side and an object-image overlay position on the other side. Means such as pivoting mirrors are provided for obtaining separate object and image positions and for making them accessible for practical installations.

According to other embodiments, the two halves of the optical system are arranged coaxially back to back so as to form an intermediate image on one of the sides and separate object and image positions on the other side. For this purpose, the intermediate image is offset axially from the other conjugate positions in at least one of the halves of the system. According to certain embodiments, the distance between the two elements of mirrors in the intermediate image is greater than the distance to the other conjugate position in at least one of the halves of the system, so as to space the object and image positions in the other half. In another embodiment the distance between the mirror elements at the intermediate position is less than the distance from the other positions combined in at least one of the halves of the system, so as to form crossed object and image planes. In this case, reflective elements are provided interposed between the object and image positions 30 so as to make them physically accessible.

It should be noted that a necessary condition for there to be no field curvature (for example for a plane image surface) in the resulting system is that the algebraic sum of the quantities obtained by dividing the power of each surface by its refractive index is substantially zero, the refractive index of the reflecting surface being defined as negative. The refractive meniscus elements, which are essential components of the optical system according to the invention, generate a chromatic variation on the aforementioned algebraic sum so that even if this sum is substantially zero, a relative variation in the curvature is observed. field by color. According to the invention, the focal point position is constant for a wide spectral band by the introduction of a longitudinal chromatic difference of the focal point, which compensates for the variation in curvature of the chromatic field 45 in the annular field of the optical system.

The present invention will be better understood with reference to the description of the exemplary embodiments and the attached drawing in which:

the fìg. 1 schematically represents an optical system produced 50 in accordance with the concepts of the present invention;

the flg. 2 schematically represents a double optical system comprising two optical systems arranged back to back and similar to the system of the fig. 1;

fig. 3 schematically represents an optical system 55 similar to the system of FIG. 2, but simplified in that the two halves are no longer symmetrical while the system as a whole remains symmetrical;

fig. 4 is a schematic representation of an optical system identical to that of FIG. 3. but simplified in that the two 60 color correction plates are combined in a single element and by the elimination of the double plates necessary to separate the object and the final image by making the combined distances of the two elements of mirrors unequal ;

fig. 5 to 7 schematically illustrate other embodiments of the optical system according to the invention;

fig. 8 is a schematic representation of an optical system similar to that of the fìg. 1 and illustrating another embodiment of the invention, and

5

625,055

fig. 9 is a graphic representation illustrating the variations in position of the focal point as a function of the distance from the axis and of the wavelength of the light used.

With reference to fig. 1, the optical system 10 comprises two spherical mirrors, a convex mirror 12 and a concave mirror 14 arranged so as to produce three successive reflections inside the system. The mirrors have their centers of curvature aligned on the axis SA and include conjugate zones arranged outside the axis at points O and I. Points O and I are arranged on either side of the axis SA and at a distance H from this axis. In the optical system illustrated in fig. 2 of US patent N <> 3748015, the concave mirror forms at point I an image of an object placed at point O; the convex mirror forms a virtual image from point I to point O, this image being reflected by the concave mirror at point I. It should be noted that the extent of the corrected ring obtainable by this optical system is limited by l fifth order astigmatism inherent in this system. High-ranking astigmatism results from spherical aberrations of the main rays of this system.

It should be noted that meniscus elements can be used to reduce or eliminate spherical aberrations of the main rays parallel to the optical axis. If the meniscus elements are concentric with the mirrors, they do not introduce third-order aberrations, except for the field curvature when the conjugates are at the common center of curvature.

As shown in fig. 1, a pair of meniscus elements 16 are arranged symmetrically to reduce spherical aberrations of the main rays. It is noted that the meniscus elements could also serve to reduce the spherical aberrations of the main rays if they were mounted directly adjacent to the convex mirror 12 so that the surface of the mirror 12 and the convex surface of the meniscus 16 are part of the same spherical surface. High-ranking astigmatism has been significantly reduced, which has the effect of increasing the extent of the corrected ring.

A necessary condition to ensure the absence of field curvature, for example to obtain a plane image surface, in the present system, is that the algebraic sum of the quantities obtained by dividing the power of each surface by its refractive index is substantially zero, the refractive index of the reflecting surface being considered as negative in this arrangement. Since the refractive index of the meniscus elements varies with the wavelength of the light used, it is obvious that the introduction of these elements into the optical system results in a variation of the field curvature with the length wave. This results in a variation of the focus as a function of the distance from the axis and as a function of the wavelength of the light used as shown in fig. 9. In an optical system with an annular field, the variation as a function of the distance from the axis is eliminated by limiting the field to a ring whose distance from the axis is constant. The variation of the field curvature as a function of the wavelength in such a system results in a variation of the position of the focal point as a function of the wavelength, which can be compensated for by the introduction of a chromatic aberration opposite direction. For this purpose, the refractive meniscus moves away from absolute concentricity in that the radius of the convex surface is less than the sum of the radius of its concave surface and its thickness. This amounts to saying that its thickness is greater than the difference between the radii of its convex surface and its concave surface, the principle of this operation is as follows:

The variation of the field curvature as a function of the wavelength entrained in an approximately concentric meniscus whose power is negative is such that the rear focus is larger for short waves than for long waves. A concentric meniscus whose conjugates are located at its center of curvature does not introduce any longitudinal chromatic aberration. This also applies to a meniscus having a conjugate near its center of curvature. The addition of a positive lens to such a meniscus introduces a longitudinal chromatic aberration in the direction necessary to compensate for the variation in focal position as a function of the wavelength resulting from the variation in the field curvature (to which contributes the meniscus) as a function of the wavelength. This can be obtained by making a meniscus whose convex radius is less than the sum of the concave radius and its thickness. This meniscus is then equivalent to two lenses, one being a fictitious concentric meniscus whose convex radius is equal to the sum of its concave radius with the thickness, while the second is a positive meniscus of zero thickness whose radius concave is equal to the convex radius of the previous fictitious meniscus and whose convex radius is equal to the convex radius of the current meniscus. For an approximately concentric meniscus having a concave radius Rt, a convex ray R2, a thickness t, and a refractive index N, the chromatic longitudinal aberration compensates for the displacement of the focal point due to the variation of the field curvature as a function of the wavelength in a ring of radius H when:

R2> Rj ett> R2-R1 + H2 / 2n2) (l / R, -l / R2) (D

The introduction of a pair of menisci whose parameters fully satisfy equation 1 in an optical system such as that described in the aforementioned patent and the making of modifications which will be described in more detail below entail a reduction in aberrations high ranking over a wide spectral band.

The system thus obtained can be considerably improved by modifying the menisci in such a way that their thickness is greater than that given by equation 1. This results in a variation of the position of the focal point in an optical system with annular field, the direction of this variation being such that it can be compensated for by the introduction of a parallel flat plate of appropriate thickness, such as plate 18 of FIG. 1. The additional degree of freedom resulting from the introduction of this additional element makes it possible to obtain a better correction.

Other improvements can be obtained by modifying the parallel flat plates in one or both of the following directions:

1. One of the faces of the parallel flat plate is made aspherical.

2. The parallel flat plate is curved and turns into a meniscus element.

The highest degree of correction was obtained with a system whose thickness of the meniscus is greater than the value obtained by equation 1 and in which the chromatic compensation is obtained by the addition of modified parallel flat plates in one or the other direction described above. The small aberrations which are due to the fact that the meniscus element 16 is not perfectly concentric, are compensated by the introduction of a small deformation of the pair of mirrors 12 and 14 which are caused to no longer be perfectly concentric . In practice, this amounts to saying that the concave mirror 14 and the convex mirror 12 are mounted in such a way that their centers of curvature are distant by a length less than two percent of the length of the shortest radius.

Table 1 below indicates the constructive data of an optical system with an annular field as shown in FIG. I. As known per se, the + sign is used to indicate that a surface is convex in relation to an object and that the distance is measured from left to right while a - sign is used to indicate that a surface is concave with respect to an object and the distance is measured from right to left.

(Table in next pay)

Table II summarizes the performance of the ring field optical systems of Table I for a wide spectral band (2800A to 5461A) in terms of RMS wave aberration for different radii of the ring. The extent of the usable ring is

5

10

15

20

25

30

35

40

45

50

55

60

65

625 055 6

Table I

Radius of the ring: 100 mm.

Surface Object no. In the image

Radius (mm)

Distance to next surface

Materials

0

(plan)

144.92

Air

Object

1

-144.96

11.03

Fused silica

2

-151.75

88.70

Air

3

-957.30

16.75

Fused silica

4

-967.84

295.25

Air

5

-551.15

-279.07

Air

Mirror

6

-267.18

279.07

Air

Mirror

7

-551.15

-295.25

Air

Mirror

8

-967.84

-16.75

Fused silica

9

-957.30

-88.70

Air

10

-151.75

-11.03

Fused silica

11

-144.96

-144.92

Air

12

(plan)

Image difference between the values of the upper and lower radii for which the performance is appropriate for the application. It should be noted that a system is called limited in diffraction, or more

As indicated above, an annular field optical system such as described above comprises at least one convex mirror and a concave mirror which are arranged in a substantially concentric manner along an optical axis so as to form planes normal to this axis, the system power being unitary. The fìg. 1 shows such an arrangement of mirrors. Fig. 8 illustrates a system which comprises a convex mirror 12e and a concave mirror 14e arranged concentrically along an optical axis SA so that a total of five -reflections are obtained inside the system, three reflections on the concave mirror 14th and two on the 12th convex mirror. In this embodiment, the algebraic sum of the powers on the reflecting surfaces used is zero when the radius of the convex mirror 12e is equal to two thirds of that of the concave mirror 14e. Analogously to what has been described with reference to FIG. 1, the system of FIG. 8 includes meniscus elements 16th and a chromatic correction plate 18th whose function is identical to that which has been described previously.

It should be noted that ring field optical systems as described are generally used for optical scanning and for this purpose it is highly desirable that the object and the image are oriented in the same way so that their physical supports can be held in position relative to each other while the optical system is mobile for the scanning operation and precise with limited opening when the rms wave aberration is less than 0.07. For a scanning system, this aberration can reach 0.09 or 0.1 at the edges of the ring.

45 so that the requirements for good accuracy of the scanning movement are minimal. A device which meets these requirements by the introduction of three plane mirrors into an optical system has been described in US Pat. No. 3,951,546. Another means for obtaining the same effect consists in using two so optical systems 10 and 10 ′, each being constituted by a system conforming to that shown in FIG. 1, arranged back to back so that the object and image planes are superimposed as shown in fig. 2. The optical system 10 comprises two spherical mirrors 12 and 14, a pair of meniscus elements 16 and a chromatic correction plate 55 18; the optical system 10 'symmetrical comprises two spherical mirrors 12' and 14 ', a pair of meniscus elements 16' and a plate 18 'of chromatic correction. The material separation between the object and "the final image, which is essential for the installation of the supports, is obtained by two pivotable mirrors 20 and 20 '60 shown in dotted lines in Fig. 2 intended to move the object and image positions at points O 'and I'. In such an arrangement the distance between the two mirrors must be sufficient to allow the scanning operation. This device of pivotable plane mirrors can obviously be replaced by other 65 means known on condition that these means preserve the orientation of the image relative to the object.

In the optical system of fig. 2, the intermediate image 22 is a highly corrected image because it is obtained by the

Table II

N.A. = 0.17 to object and image

RMS wave aberration (wavelength units)

Radius of

the ring (mm)

Wavelength (Angstrom units)

2800

3200

3650

4000

4358

5461

105

.09

.12

.13

.13

.13

.12

104

.05

.08

.09

.09

.09

.08

103

.02

.04

.05

.06

.06

.05

100

.02

.01

.01

.01

.01

.01

97

.04

.01

.02

.02

.02

.03

96

.06

.02

.02

.03

.03

.03

95

.08

.04

.04

.04

.04

.04

94

.11

.06

.05

.05

.05

.05

93

.13

.08

.07

.07

.06

.06

7

625,055

optical system 10 conforming to the system of FIG. 1. In this device each half 10 and 10 'of the optical system is symmetrical and therefore reversible. Since, for most applications, a high degree of correction at the intermediate image level is not required, the system can be simplified and perfect symmetry of the two halves is not absolutely required; however, the system or at least the refracting components must have overall symmetry, which makes it possible to reduce the number of compensating menisci and the number of correction plates to two as shown in the embodiment of FIG. 3. One half of the optical system referenced under 10a comprises two spherical mirrors 12 and 14, a meniscus element 16a and a chromatic correction plate 18a disposed on the side of the intermediate image 22, all of these elements being arranged symmetrically from the optical axis SA. The other half of the optical system referenced 15 under 10a 'comprises two spherical mirrors 12' and 14 ', a meniscus element 16a' and a chromatic correction plate 18a '

disposed next to the intermediate image 22, all these elements being arranged symmetrically under the optical axis SA. For the same reasons as before, each half of the optical system 20

comprises a pivotable mirror 20 and 20 ′ illustrated in dotted lines in FIG. 3 to shift the positions of the object and the final image respectively at points O 'and I'.

With reference to the embodiment illustrated in FIG. 4, it should be noted that these intermediate image systems 22 can be further simplified by the combination of the color correction plates 18a and 18a 'as shown in FIG. 3 in a single element 18b of identical shape as shown in FIG. 4. The symmetry is maintained by placing this chromatic correcting element 18b at the location or in the immediate vicinity 30 of the intermediate image 22. In addition, the inclined mirrors 20 and 20 'of FIG. 3 can also be eliminated by making the combined distance of at least one of the two mirrors 12b, 14b or 12b ', 14b' uneven. As a result, the distance from the intermediate image to the pairs of mirrors is made greater than the object and / or image distance and therefore the final image I is offset from the object O. In this system, the color correction plate 18b arranged in the intermediate image can be a real flat plate with parallel faces.

In a true afocal system, the magnification is the same for all the conjugate positions. However, this is generally not achieved in practice because true afocal systems do not remain true for all positions in the field. For the unit magnification system shown in fig. 4 for example, if an object O and an image I are brought together lengthwise by 1 mm, the magnification of a ring of 4 mm varies ± 0.00032. This variation which results from the scanning tolerances can be reduced to ± 0.00001 by making one of the faces of the chromatic correction plate 18b aspherical. A modification of the optical system illustrated in FIG. 4 is shown in FIG. 5 where the correction menisci are moved to the other side of the intermediate image relative to the optical axis. In this embodiment, half of the system comprises two spherical mirrors 12b and 14b and a meniscus element 16c arranged on the side of the object and of the image symmetrically above the optical axis SA and the other half of the system comprises two spherical mirrors 12b 'and 14b' and a meniscus element 16c 'also arranged on the side of the object and of the image symmetrically above the optical axis SA. A chromatic correction plate 18b is arranged symmetrically below the optical axis in a position very close to that of the intermediate image 22. As in the embodiment of FIG. 4, one of the faces of this plate is made aspherical. On the other hand,

as in the embodiment of fig. 4, the distances from the intermediate image to the pairs of mirrors are greater than the object-image distances so as to shift the position of the final image I from that of the object O, to allow scanning.

Table III provides the constructive data of an optical system conforming to that illustrated in FIG. 5.

Table III

Ring radius = 100 mm.

Surface Object no. In the image

Radius (mm)

Distance to next surface

Materials

0

(plan)

107.13

Air

Object

1

-128.18

10.48

Fused silica

2

-135.29

378.48

Air

3

-541.32

-273.56

Air

Mirror

4

-264.61

273.56

Air

Mirror

5

-541 — .32

-590.28

Air

Mirror

6

-1772.58 *

7.01

Fused silica

7

(plan)

-587.26

Air

Aspherical

8

541.32

273.56

Air

Mirror

9

541.32

273.56

Air

Mirror

10

541.32

378.48

Air

Mirror

11

135.29

10.48

Fused silica

12

128.18

107.13

Air

13

(plan)

Picture

* Aspherical surface symmetrically arranged on the optical axis Deviation, X, with respect to the plane surface at distance r from the axis:

X = - 1772.58 -t- V1772.58 - r- + 1.732xl0-8r4 + 4.210xl0-13r6 + 8.278x10-I8r4-4.078xl0-2Ir10

Table IV represents the performance of ring field optical systems defined by Table III for a wide spectral band (2800A to 5461A) in terms of RMS wave aberrations for different radii of the ring. The extent of the usable ring is the difference between the values of the upper and lower radii for which the performance is appropriate for a given application.

625,055

Table IV

N.A. = 0, I7 to the object and to the image

Ring radius (mm)

RMS wave aberration (wavelength units)

Wavelength (Angstrom units)

2800

3200

3650

4000

4358

5461

103

.08

.08

.08

.08

.08

.07

102

.06

.05

.05

.05

.04

.04

100

.05

.04

.04

.03

.03

.03

98

.06

.04

.04

.04

.04

.06

97

.09

.06

.05

.05

.05

.06

96

.13

.09

.08

.07

.07

.07

Fig. 6 represents an optical system in which the distances between on the one hand the intermediate image and on the other hand the pairs of mirrors 12d-14d and 12d'-14d 'are less than the distances between the object O and the final image I. In the embodiment of FIG. 6, one half of the system comprises two spherical mirrors 12d and 14d and a meniscus element 16a disposed on the side of the intermediate image. A single chromatic correction plate 18b is placed in the immediate vicinity of the intermediate image 22. Two parallel reflecting flat surfaces, similar to those described with reference to FIGS. 2 and 3 are introduced between the two conjugate positions O and I. so that they are accessible for scanning. Furthermore in the embodiment of FIG. 6, these two flat surfaces are constituted by front and rear surfaces of a flat parallel plate 20d whose thickness is determined by mechanical considerations, contrary to the arrangements of FIGS. 2 and 3 where other considerations determined the distance between the reflecting surfaces. In this embodiment, the front and rear surfaces of the plate 20d respectively reflect the object O at point O 'and the final image I at point I', which provides the space necessary for scanning.

Another embodiment in which the object and image planes are crossed is shown in FIG. 7. In this device, the chromatic correction plate 18b of FIG. 6 arranged in the immediate vicinity of the intermediate image has been replaced by two correcting plates 18e and 18e 'placed on the object-image side of the system. In this embodiment, the parallel flat plate has been curved so as to produce a meniscus element. The other elements of FIG. 7 are identical to those of FIG. 6. That is to say that one of the halves comprises two spherical mirrors 12d and 14d and a meniscus element 16a disposed on the side of the intermediate image, and the other part of the system also comprises two spherical mirrors 12d 'and 14d' and a meniscus element 16a '30 also arranged on the side of the intermediate image. As previously described with reference to FIG. 6, the plate 20d has front and rear reflecting surfaces which make it possible to reflect the object O in O 'and the final image I in the so that the two points O' and the are distinct and allow d 'interpo-35 ser practical mounting elements.

Table V provides the constructive data of an optical device with an annular field conforming to FIG. 7.

Table V

Ring radius = 100 mm.

Surface N »

Radius (mm)

Distance to next surface

Materials

Note

0

(plan)

151.33

Air

Object

1

-726.89

28.69

Fused silica

i

-730.32

410.82

Air

3

-552.06

-280.16

Air

Mirror

4

-276.18

280.16

Air

Mirror

5

-552.06

-363.25

Air

Mirror

6

-160.78

-24.03

Fused silica

7

-145.19

-272.77

Air

8

145.19

-24.03

Fused silica

y

160.78

-363.25

Air

10

552.06

280.16

Air

Mirror u

267.18

-280.16

Air

Mirror

12

552.06

410.82

Air

Mirror

13

730.32

28.69

Fused silica

14

726.89

151.33

Air

15

(plan)

Picture

Table VI shows the performance of the annular field optical system defined in Table V for a wide spectral band (2800A to 5461A) in terms of RMS wave aberrations for different radii of the ring. The extent of the usable ring is the difference between the values of the upper and lower radii for which the performance is adequate for the application.

9

625,055

Table VI

N.A. = 0.17 to object and image

RMS wave aberration (wavelength units)

Radius of

the ring (mm)

Wavelength (Angstrom units)

2800

3200

3650

4000

4358

5461

104

.08

.07

.09

.10

.10

.11

103

.06

.04

.05

.06

.07

.08

102

.05

.02

.03

.04

.05

.06

100

.03

.02

.02

.02

.03

.04

98

.07

.04

.03

.03

.02

.03

97

.10

.06

.05

.04

.04

.03

96

.14

.09

.07

.06

.06

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It should be noted that in the arrangements of fig. 7 and 5 the elements as windows for aligning the parts of the optical system between refracting meniscus 18th, 18th, 16c and 16c can be used.

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7 sheets of drawings

Claims (25)

625,055 2 1. An optical device with an annular field for exposing a photographic image-receiving surface to a light image of an object, characterized in that it comprises at least one convex mirror and one concave mirror (12,14; 12 ', 14 '; 12b, 14b; 12b', 14b '; 12d, 14d; 12e, 14e), these mirrors being arranged substantially concentrically with respect to the optical axis (SA), the optical device (10, 10', 10a, 10a ', 10b, 10b', 10c, 10c ', 10e, 10e', lOf, lOf) being arranged so as to form conjugate planes perpendicular to this axis and so that its power is unitary, and at least a pair of meniscus elements (16,16 ', 16a, 16a', 16c, 16c ') arranged substantially concentrically whose convex rays are greater than the concave rays and whose thickness is greater than the difference between the concave rays and convex rays. 2. Optical device according to claim 1, characterized in that it comprises a first and a second half, each of these halves comprising one of the convex mirrors and one of the concave mirrors as well as at least one of the elements of menisci, and an optical unit having an axis and forming conjugate planes substantially perpendicular to the optical axis, for which the optical unit has a substantially unitary power, the two halves being arranged coaxially back to back so that the planes conjugates are superimposed on at least one of the sides of the optical device, forming an intermediate image there. 3. Optical device according to claim 1 or 2, characterized in that the rays emitted from the position of an object are reflected from the concave mirror on the convex mirror and that after several reflections between the concave mirror and the convex mirror the rays are focused on the position of the image. 4. Optical device according to claim 3, characterized in that the light emitted by said object is reflected at least twice on the concave mirror and at least once on the convex mirror. 5. Optical device according to claim 3 or 4, characterized in that the mirrors are arranged so that there are three reflections on the concave mirror and two reflections on the convex mirror. 6. Optical device according to one of claims 1 to 5, characterized in that said convex and concave mirrors are mounted in such a way that their centers of curvature are distant by a length at most equal to 2% of the smallest radius. 7. Optical device according to claim 1, characterized by a pair of meniscus elements arranged symmetrically to the optical axis. 8. Optical device according to claim 2, characterized in that each of these halves comprises a single meniscus element arranged symmetrically to the superposed conjugate planes. 9. Optical device according to claim 2, characterized in that each of these halves comprises a pair of meniscus elements arranged symmetrically to the optical axis of each half and that each pair is arranged symmetrically to the superposed conjugate planes. 10. Optical device according to one of claims 7 to 9, characterized in that the meniscus elements are mounted in conjugate positions so as to minimize their contribution to astigmatism. 11. Optical device according to one of claims 1 to 10, characterized in that the relationship between the radius of the annular field and the characteristics of the concentric meniscus element is defined by the following formulas: R2> R, and t> R, - R1 + (H2 / 2N2) (1 / R „- 1 / R2) OR 'H = the annular radius of the system, R, = the concave radius of the meniscus, R2 = the convex radius of the meniscus, t = the thickness of the meniscus, and N = the refractive index of the meniscus. 12. Optical device according to claim 1, characterized in that it comprises a chromatic compensation device placed between the mirrors and the object-image arrangements. 13. Optical device according to claim 12, characterized in 5 that the chromatic compensation device is arranged between the mirrors and the meniscus elements. 14. Optical device according to claim 2, characterized in that said first and second halves each comprise a chromatic compensation device. 15. Optical device according to claim 14, characterized in that the chromatic compensation device is arranged in each half between the intermediate image position or the object, respectively the image and the mirrors. 16. Optical device according to claim 14, characterized in that 15 that the chromatic compensation device is arranged in each half between the mirrors on one side and the intermediate image position, respectively the object and the image on the other side. 17. Optical device according to claim 14, characterized by a single chromatic compensation device disposed at the 20 intermediate image position. 18. Optical device according to one of claims 13 to 17, characterized in that the chromatic compensation device consists of a parallel flat plate. 19. Optical device according to one of claims 13 to 17, 25 characterized in that the chromatic compensation device is a plate with an aspherical surface. 20. Optical device according to one of claims 13 to 16, characterized in that the chromatic compensation device consists of a meniscus. 21. Optical device according to one of claims 18 to 20, characterized in that the plate, respectively the meniscus, is mounted normally with respect to the optical axis of the mirrors. 22. Optical device according to claim 2, characterized in that the distance between the object or the image and the associated concave mirror 35 in at least one half differs from the distance between the intermediate image position and the concave mirrors. 23. Device according to claim 2, characterized in that the distance between the object, respectively the image, and the associated concave mirror is equal to or greater than the distance between the image position 40 intermediate and concave mirrors, and that a positioning device is provided for shifting the distance between the image position and the object position so as to make these positions physically accessible. 24. Optical device according to claim 23, characterized in that 45 that the device for positioning is constituted by reflective surfaces. 25. Optical device according to one of claims 1 to 24, characterized in that the algebraic sum of the quantities obtained by dividing the power of each surface by the refractive index is jo substantially zero, the refractive index of the surface reflective being defined as negative. 26. Optical device according to claims 4 and 12, characterized by the following constructive data: (Table at the top of the next page) 55 27. Optical device according to claims 2,4, 8,17 etl8, characterized by the following constructive data: (Table on next page) 60 28. Optical device according to claims 2,4, 8, 15 and 20, characterized by the following constructive data: Radius of the ring = 100 mm. (Table on next page)