Three-dimensional interferometer and method for determining a phase of an electric field

Abstract

A three-dimensional interferometer for measuring a light field produced by an object, comprising a first interferometer arm, a second interferometer arm, a beam splitter arranged between an object point of the object and the first interferometer arm and the second interferometer arm, and is set up to split a beam coming from the object point at the beam splitter into the first beam and the second beam, a detection plane or a detection surface which is arranged downstream of the first interferometer arm and the second interferometer arm and is set up in such a manner that the first beam and the second beam are made to interfere in an interference region on said plane or surface, and an overlapping device which is arranged between the detection plane and the first interferometer arm and the second interferometer arm.

Claims

1. An interferometer for measuring a light field produced by an object, the interferometer comprising: a first interferometer arm arranged to pass through a first beam; a second interferometer arm arranged to pass through a second beam; a beam splitter arranged between an object point of the object and both of the first interferometer arm and the second interferometer arm, wherein the beam splitter is configured to split a light beam emanating from the object point into the first light beam and the second light beam; a detection surface located after the first interferometer arm and the second interferometer arm, wherein the detection surface is arranged so that the first light beam and the second light beam are brought to interference on an interference area of the detection surface; and an overlap device located between the detection surface and both of the first and second interferometer arms; wherein the beam splitter, the first interferometer arm, the second interferometer arm, the overlap device, and the detection plane are configured such that: there is an initial central ray emanating from the object point, wherein the initial central ray is divided at the beam splitter into a first central ray and a second central ray; the initial central ray is part of the light beam, the first central ray is part of the first light beam and the second central ray is part of the second light beam; the first central ray and the second central ray overlap on the detection plane in the interference area in a central image point; for each light ray that emanates from the object point of the object and is part of the light beam, but is not the central ray, the beam splitter splits each light ray that is not the central ray into a first light ray and a second light ray, wherein each first light ray passes through the first interferometer arm and each second light ray passes through the second interferometer arm, and wherein corresponding first and second light rays strike the detection surface at different points; for each image point of the interference area that is not the central image point, there is a third light ray and a fourth light ray, each of which are not the central ray; the third light ray emanates from the object point, passes through the first interferometer arm and the image point, and strikes the detection plane; the fourth light ray emanates from the object point passes through the second interferometer arm, and overlaps with the third light ray at the image point on the detection surface; and the third light ray and the fourth light ray are part of the light beam before the beam splitter.

2. The interferometer of claim 1, also comprising: an evaluation unit configured to measure at least one of a phase difference between two interfering light rays or a phase of a light ray striking at least one point of the interference area of the detection surface.

3. The interferometer of claim 1, further comprising a detector configured to detect light impinging on the detection surface.

4. The interferometer of claim 1, wherein at least one of the first interferometer arm or the second interferometer arm comprise at least one ray deflection element.

5. The interferometer of claim 1, wherein the interferometer is configured so that a sum of ray deflections for a fifth light ray that is the central ray before the beam splitter and is the first central ray after the beam splitter, wherein the fifth light ray is only considered between a point immediately before the beam splitter and immediately after the overlap device, and for a sixth light ray that is the central ray before the beam splitter and is the second central ray after the beam splitter, wherein the sixth ray is only considered between a point immediately before the beam splitter and immediately after the overlap device, is equal to one of 5, 6 or 7.

6. The interferometer of claim 1, wherein an incident plane, which is defined by the first central ray and the second central ray directly after the beam splitter, and an exit plane which is defined by the first central ray and the second central ray directly before the overlap device are unequal.

7. The interferometer of claim 1, wherein at least one of the first interferometer arm (150) or the second interferometer arm includes a device for changing an optical path of the corresponding interferometer arm.

8. The interferometer of claim 1, further comprising a device for at least one of the relative displacement, relative stretching, relative tipping or relative rotation of an existing first light field on the detection surface that originates from the first light beam and of an existing, second light field on the detection surface that originates from the second light beam.

9. The interferometer of claim 1, wherein the interferometer comprises at least a portion of a holographic camera.

10. A method of using the interferometer of claim 1 for determining a phase difference .sub.ij for at least one image point of a pixel grid of a detection surface in an interference area between a first electric field E1.sub.ij and a second electric field E2.sub.ij, which interfere at the at least one image point, wherein the first electric field originates from a first interference arm and the second electric field E2.sub.ij originates from a second interference arm.

11. A method of using the interferometer of claim 1 for determining a phase of an electric field (E1.sub.ij,E2.sub.ij) in a part of an interference area on a detection surface of a three-dimensional interferometer, the method comprising: for a part of the interference area, determining at least one of an intensity or an absolute value of a first electric field (E1.sub.ij), which originates from a first interference arm, and a second electric field (E2.sub.ij) which originates from a second interference arm; for the part of the interference area, determining an interference term (IF) according to the equation:
IF.sub.ij=|E1.sub.ij|.Math.|E2.sub.ij|.Math.exp(i.Math.ij), wherein .sub.ij is a phase difference between the phase (1.sub.ij) of the first electric field (E1.sub.ij) and the phase (2.sub.ij) of the second electric field (E2.sub.ij) that can be determined, especially with the help of the method according to claim 10; determining a propagation matrix (U), wherein an element of the propagation matrix (U) states how, for a given pixel grid of the interference area, the first electric field E1.sub.ij at a pixel with the indices i and j can be transformed into a second electric field E2.sub.ij at a pixel with the indices m and n, and for the part of the interference area, solving of the equation ${.Math.E{1}_{\mathrm{ij}}.Math.}^2.Math.\underset{m,n}{.Math.}\stackrel{\_}{U_{\mathrm{ij},m,n}}.Math.\stackrel{\_}{E{1}_{\mathrm{mn}}}=1F_{\mathrm{ij}}.Math.\stackrel{\_}{E{1}_{\mathrm{ij}}}$ after the complex first electric field (E1.sub.ij).

12. A non-transitory computer-readable medium storing a computer program that, when executed by a computer, performs the method according to claim 10.

13. A non-transitory computer-readable medium storing a computer program that, when executed by a computer, performs the method according to claim 11.

Description

(1) The present invention will now be further explained using individual examples and figures. These examples and figures serve only to illustrate the general invention concept without the examples and figures of the invention being interpreted as a limitation in any way.

(2) FIG. 1 shows a schematic illustration of an embodiment of an invention-related interferometer as an illustration of the main claim.

(3) FIG. 2 shows a schematic illustration of an embodiment of an invention-related interferometer as an illustration of the first condition of the main claim.

(4) FIG. 3 shows a schematic illustration of an embodiment of an invention-related interferometer as an illustration of the second condition of the main claim.

(5) FIG. 4 shows a schematic illustration of an embodiment of an invention-related interferometer as an illustration of the third condition of the main claim.

(6) FIG. 5 shows a schematic, which illustrates a projective mapping of the first electric field onto the second electric field.

(7) FIG. 6 shows a schematic of an embodiment of an invention-related interferometer in which both the beam splitter and the overlap device each have a diffraction grating.

(8) FIG. 7 shows a schematic of an embodiment of an invention-related interferometer in which the incident plane and the exit plane are not identical, but parallel to each other.

(9) FIG. 8 shows the schematic of an embodiment of an invention-related interferometer, which can be built compactly and in which the incident plane and the exit plane are perpendicular to each other.

(10) FIG. 9 shows a schematic of an embodiment of an invention-related interferometer with a monolithic structure.

(11) FIG. 1 shows a three-dimensional interferometer 100, which measures an interferometric light field produced by an object 110. As already described in the general description part, a special light field is used to characterize the invention-related three-dimensional interferometer. This is a light beam emanating from an object point 112 of the object 110, which is not shown in FIG. 1 for reasons of clarity. In FIG. 1, only a central ray 114 is shown, which is part of the beam. The central ray 114 runs out from the object point 112 to a beam splitter 101 at which it is split into a first central ray 120 and a second central ray 121.

(12) One of the beam splitters 101 can be a beam splitter cube or a glass plate, which preferably has a coating matched to the light rays used.

(13) The central ray 114 is split in amplitude at the beam splitter 101. The second central ray 121 is deflected here through a certain angle relative to the direction of the central ray 114, while the first central ray 120 has the same direction as the central ray 114. An incident plane 154 is defined by the first central ray 120 and the second central ray 121. The incident plane 154 is indicated graphically by a dashed line. In addition, a cross is located on the plane which calcifies the orientation of the incident plane 154.

(14) The first central ray 120 runs into the first interferometer arm 150 after the beam splitter 101. The second central ray 121 runs into the second interferometer arm 152 after the beam splitter 101.

(15) After the beam splitter 101, the first central ray 120 is deflected at a first ray deflection element 171 and a second ray deflection element 172, which are both positioned in the first interferometer arm 150. After the beam splitter 101, the second central ray 121 is deflected at a first ray deflection element 181 and a second ray deflection element 182, which are both positioned in the second interferometer arm 152. As already explained above, a certain number of ray deflection elements are necessary to rotate the distribution of the first and second electric fields.

(16) The first central ray 120 is deflected by the second ray deflection element 172 in the first interferometer arm 150 and the second central ray 121 is deflected by the second ray deflection element 182 in the second interferometer arm 150 onto an overlap device 106. From there, the first central ray 120 and the second central ray 121 are deflected onto a detection plane 131 of a detector 130. As already discussed above, the first central ray 120 and the second central ray 121 meet in a common image point which is named central image point 133.

(17) Generally, two incident light rays falling onto the overlap device directly after the overlap device do not become a single light ray. This also applies generally for two central rays, i.e. for the first central ray 120 and the second central ray 121. There is however an exception for case in which the central ray 114 is emitted by a central object point (not illustrated). It can be shown that the central object point is unique. It does not, however, have to lie in the field of view of the invention-related interferometer.

(18) In the embodiment of FIG. 1, the second central ray 121, which falls onto the overlap device 106 from the second ray deflection element 182 in the second interferometer arm 152, is not deflected at the overlap device 106.

(19) The first central ray 120 however, which comes into the first interferometer arm 150 from the second ray deflection element 172 in the first interferometer arm 150 and falls onto the overlap device 106, is deflected at the overlap device 106 in the direction of the central image point 133 of the direction plane 131.

(20) The first central ray 120 directly before overlap device 106 and the second central ray 121 directly before the overlap device 106 define an exit plane 155. The exit plane 155 is indicated graphically by a dashed line. The incident plane 154 intersects the exit plane 155 in a straight line which corresponds to the y-axis of the coordinate system drawn in the figure. The exit plane 155 is arranged here in the x-y plane. The fact that the incident plane 154 is not coincident with the exit plane 155 corresponds to the definition of a three-dimensional interferometer.

(21) The first interferometer arm 150 begins at beam splitter 101 and extends at least as far as the overlap device 106, strictly speaking however as far as detection plane 131. The second interferometer arm 152 begins at beam splitter 101 and extends at least as far as the overlap device 106, strictly speaking however as far as detection plane 131.

(22) The three-dimensional interferometer 100, according to the embodiment of FIG. 1, has a total of six ray deflections. The first central ray 120 (which is the central ray 114 before the beam splitter 101) is not deflected at the beam splitter 101; however once in each case at the first ray deflection element 171 and at the second ray deflection element 172 in the first interferometer arm 150 and at the overlap device 106. The first interferometer arm 150 therefore has a total of three ray deflections.

(23) The second central ray 121 (which is the central ray 114 before the beam splitter 101) is deflected at the beam splitter 101; once in each case at the first ray deflection element 181 and at the second ray deflection element 182 in the second interferometer arm 152 but not at the overlap device 106. The second interferometer arm 152 therefore also has a total of three ray deflections. The first interferometer arm 150 and the second interferometer arm 152 therefore have a total of six ray deflections.

(24) FIGS. 2 to 4 show schematics of an embodiment of an invention-related interferometer to illustrate the three conditions of the main claim described in the general description part.

(25) FIG. 2 here illustrates the first condition, FIG. 3 the second condition and FIG. 4 the third condition.

(26) Just as in FIG. 1, an object 110 with an object point 112 can be seen at the upper end of FIG. 2, from which a central ray 114 emanates that is split at beam splitter 101 into a first central ray 120 and a second central ray 121. The beam splitter 101 is shown here in a simplified form.

(27) The first interferometer arm 150 is also shown very much simplified and has only one first ray deflection element 171, which is also shown very much simplified. The second interferometer arm 152 is also shown very much simplified and has only one first ray deflection element 181, which is also shown very much simplified.

(28) The first central ray 120 and the second central ray 121 are also deflected by an overlap device 106 (shown in simplified form) onto a detection plane 131 of a detector 130.

(29) The first condition is that the beam splitter 101, the first interferometer arm 150, the second interferometer arm 152, the overlap device 106 and the detection plane are preferably so configured or adjusted, preferably configured, that for every object point 112 of the object 110 there is exactly one central ray 114 emanating from the object point 110, which is split at the beam splitter 101 into a first central ray 120 and a second central ray 121, wherein the first central ray 120 and the second central ray 121 overlap on the detection plane 131 in the interference area 132 in a central image point 133. It can be seen that the first central ray 120 and the second central ray 121 meet on the detection plane 131 in the central image point 133, wherein the propagation directions of the two central rays 120, 121 are not the same. This corresponds to the definition of overlapping. For the exceptional case that the object point 112 is a central object point, the first central ray 120 and the second central ray 121 would have the same direction at the central image point 133; they would therefore be superposed. In the embodiment of FIG. 2 however, the general case is shown in which the object point 112 is not a central object point.

(30) It should be emphasized that, in the embodiments of FIGS. 2 to 4, the incident plane does also not coincide with the exit plane. In the FIGS. 2 to 4, the first ray deflection element 171 in the first interferometer arm 150 and the first ray deflection element 181 in the second interferometer arm 152 stand representative for any possible further ray deflection elements. Because of this simplified method of representation, it cannot be seen clearly that the incident plane does not coincide with the exit plane.

(31) FIG. 3 illustrates the second condition of the main claim. This says that for each light ray 115 that leaves the object point 112 of the object 110 and is part of the light beam, but is not the central ray 114, there are a first light ray 125 running through the first interferometer arm 150 and a second light ray 126 running through the second interferometer arm 152, which are split off from the light ray at the beam splitter 101 and which strike the detection plane 131 at different points 134, 135.

(32) Compared to FIG. 2, the light ray 115 is added in FIG. 3, which is part of the light beam (not drawn) and which is not the central ray 114. The light ray 115 is divided at the beam splitter 101 into the first light ray 125 and the second light ray 126, wherein the first light ray 125 runs through the first interferometer arm 150 and the second light ray 126 runs through the second interferometer arm 152. After that, the first light ray 125 and the second light ray 126 are deflected at the overlap device 106 in the direction of the detection plane 131, wherein the first light ray 125 strikes the detection plane 131 at an image point 134 that is not the central image point 133 and the second light ray 126 strikes the detection plane 131 at an image point 135 that is not the central image point 133 and is also not the image point 134.

(33) FIG. 4 illustrates the third condition of the main claim. This says that for each image point 134 of the interference area 132 that is not the central image point 133, there is exactly a third light ray 116 that emanates from the object point 112, is not the central ray 114, runs through the first interferometer arm 150 and strikes the image point 134 on the detection plane 131 and there is exactly a fourth light ray 117 that emanates from the object point 112, is not the third light ray 116 before the beam splitter, not the central ray 114, runs through the interferometer arm 152 and overlaps with the third light ray 116 at the image point 134 on the detection plane 131.

(34) Simply expressed, the third condition says that for each image point 134, which is not the central image point 133, there is exactly a third light ray 116 and exactly a fourth light ray 117 which overlap in the image point 134. Neither the third light ray 116 nor the fourth light ray 117 is the central ray 114 here. In addition, the third light ray 116 runs through the first interferometer arm 150 and the fourth light ray 117 through the second interferometer arm 152.

(35) The third light ray 116 and the fourth light ray 117 are part of the beam before the beam splitter 101. In the first interferometer arm 150, the third light ray 116 is part of the first light beam. In the second interferometer arm 152, the fourth light ray 117 is part of the second light beam.

(36) These three conditions illustrated and explained above characterize an interferometer according to the invention.

(37) According to the alternative formulation of the main claim, the beam splitter, the first interferometer arm, the second interferometer arm, the overlap device and the detection plane are so configurable or adjustable, preferably so configured, that a first electrical field that originates from the first beam and a second electrical field that originates from the second beam are each mutually transferable on the detection plane by a projective mapping P, wherein the projective mapping P in the interference area has exactly one fixed point, which is called the image point

(38) FIGS. 5a to 5d show schematics which illustrate a projective mapping of the first electric field onto the second electric field.

(39) Here, starting with FIG. 5a, in which a first electric field E1(x) is shown, it is indicated how the second electric field E2(y) shown in FIG. 5d can be obtained via the intermediate steps of FIGS. 5b and 5c, by means of a general projective mapping.

(40) FIG. 5a shows the detection plane 131 on which a field distribution 200 of the first electric field E1(x) is dependent on the location vector x, which has a first component x1 and a second component x2. The coordinate origin is drawn in the bottom left corner of the detection plane 131. The distribution 200 shown is not a real electric field, but is solely to clarify a spatial structure. This spatial structure shown is easily discernible and can therefore be easily followed visually in the following transformation steps. For further clarification, the coordinates are emphasized of the first electric field at location x.sub.0, which corresponds to the reticle shown.

(41) A general projective mapping P can be shown as a sequence of a displacement, a rotation about a defined point and a concluding projection onto another plane.

(42) Starting from the FIG. 5a, the field distribution of the first electric field E1(x) in the FIG. 5b is only shifted by a constant vector. This vector has a large x1 component and a smaller x2 component.

(43) Only when it is a complete projective mapping, is the transformed field distribution a real field distribution, namely the field distribution of the second electric field on the detection plane 131. As the projective mapping which is not yet complete at this point, the field distribution has to be an intermediate product which is designated as field distribution 202 of the transformed first electric field.

(44) Starting from the FIG. 5b, the field distribution 202 of the transformed first electric field is rotated about a defined point so that the field distribution 202 of the transformed first electric field is obtained, as shown in FIG. 5c.

(45) The following step from FIG. 5c to FIG. 5d is the most complicated as it contains a projection. Starting from FIG. 5c, the projection is designed as follows so that the result of the projection of the field distribution 202 of the FIG. 5c in the detection plane 131 can be seen in FIG. 5d.

(46) The projection of FIG. 5c onto 5d is made clear by the following example. A projection can be illustrated with the example of a book page. If a book page is looked at and is rotated in space and the contour then looked at, the contour depicts a projection of a rectangle. The step from FIG. 5c to FIG. 5d illustrates exactly this. Starting out from FIG. 5c, the detection plane 131 is shifted and rotated in space, which can be easily seen from the four corners of the detection plane 131 of FIG. 5c. The field distribution 202 of the transformed first electric field was then projected onto the original detection plane 131, which then leads to the field distribution shown in FIG. 5d. The field distribution shown in FIG. 5d can be regarded on the one hand as a field distribution 202 of the transformed first electric field, wherein the transformation represents the complete projective mapping P; on the other hand, this field distribution can also be regarded as the field distribution 204 of the second electric field on the detection plane 131.

(47) The field distribution 204 of the second electric field on the detection plane 131 can however, in the original coordinate system with the components x1 and x2, also be described in a transformed coordinate system with the components y1 and y2.

(48) It can be seen in FIG. 5d that the reticle, which originally described the first electric field at location x.sub.0, now describes the second electric field at the location y.sub.0. Here, the first coordinate system with the components x1 and x2 and the second coordinate system with the components y1 and y2 are converted into each other by a projective mapping P or its inverse projective mapping P.sup.1. As the projective mapping P is invention-related bijective, there is always an inverse projective mapping P.sup.1 to a project mapping P.

(49) FIG. 6 shows a schematic of an embodiment of an invention-related interferometer in which both the beam splitter and the overlap device each has a diffraction grating. The embodiment of FIG. 6 resembles the representation of the embodiment in FIG. 1. It differs from FIG. 1 however in that both the beam splitter 101 and the overlap device 106 have diffraction gratings 192.

(50) In addition, the first interferometer arm 150 has only a first ray deflection element 171, but no second ray deflection element 172. Equally, the second interferometer arm 152 has only a first ray deflection element 181, but no second ray deflection element 182.

(51) Here, the diffraction grating 192 of the beam splitter 101 can be used in such a way that the incident ray in the first and minus-first order is diffracted, and the zero order practically suppressed or not used. It is preferred here when the intensities in the first and minus-first order are approximately equal.

(52) In addition, the diffraction grating 192 of the overlap device 106 can be used in reverse to the normal ray guidance. Here, for example, the first and minus-first diffraction order can be used as the two rays to be combined and a commonly incident ray as the exiting combined ray. Here however, possible differences between the beam splitter 101 and the overlap device 106 are to be taken into consideration.

(53) In the embodiment of FIG. 6, the incident plane 154 and the exit plane 155 intersect in a straight line which corresponds to the y-axis.

(54) The total number of ray deflections in the embodiment of FIG. 6 is also six, as in the embodiment of FIG. 1. It is to be noted in this respect that two ray deflections correspond to each diffraction grating 192, which amounts to four ray deflections in total. In addition, there is still a ray deflection at the first ray deflection element 171 in each case in the first interferometer arm 150 and at the first ray deflection element 181 in the second interferometer arm 152.

(55) FIG. 7 shows a schematic of an embodiment of the invention-related interferometer, for which the incident plane 154 and the exit plane 155 are not identical, but are parallel to each other.

(56) The special point about the embodiment of FIG. 7, is that the incident plane 154 and the exit plane 155 do not intersect; they are however also not identical. This condition can only be fulfilled when these are parallel to each other, which is the case here.

(57) The embodiment of FIG. 7 has an object 110 with an object point 112 in the bottom left corner, from which a central ray 114 strikes a beam splitter cube acting as beam splitter 101. While the second central ray 121 from the beam splitter 101 is not deflected and enters the second interferometer arm 152, the first central ray 120 is deflected to the left in the direction of the first ray deflection element 171 in the first interferometer arm 150.

(58) The incident plane 154 is spanned by the first central ray 120 and the second central ray 121 directly after the beam splitter 101.

(59) The first central ray 120 is deflected in the first interferometer arm 150 by the first ray deflection element 171 out of the incident plane 154 upwards in the direction of the second ray deflection element 172 in the first interferometer arm 150. The center of the second ray deflection element 172 is located in the exit plane 155. The first central ray 120 is then deflected by the second ray deflection element 172 in the direction of overlap device 106 acting as beam splitter, through which it however passes undeflected to then strike the detection plane 131.

(60) The second central ray 121 strikes in the second interferometer arm 152 of beam splitter 101 coming firstly onto the first ray deflection element 181 and then on the second ray deflection element 182, after which it is reflected from this onto the overlap device 106. While the first ray deflecting element 181 lies in the incident plane 154, the second ray deflection element 182 is located in the exit plane 155. After the overlap device 106, the second central ray 121 is deflected onto the detection plane 131.

(61) In the embodiment of FIG. 7, the exit plane 155 is located above the incident plane 154. This is indicated by dashed arrows, which can be easily recognized, especially at the first central ray 120 between the second ray deflection element 172 and the overlap device 106.

(62) In addition, also the embodiment of FIG. 7 has a total of six ray deflections for both interferometer arms 150, 152. Here, the two beam splitter cubes of the beam splitter 101 and of the overlap device 106 each have one ray deflection. The remaining four ray deflections are achieved by the first ray deflection element 171 and the second ray deflection element 172 in the first interferometer arm 150 and the first ray deflection element 181 and the second ray deflection element 182 in the second interferometer arm 152.

(63) FIG. 8 shows the schematic of an embodiment of an invention-related interferometer, which can be built compactly and in which the incident plane and the exit plane are perpendicular to each other.

(64) The embodiment of FIG. 8 has a central object point in the field of view.

(65) The embodiment of FIG. 8 has an object 110 at the upper edge with an object point 112, from which a central ray 114 strikes a beam splitter 101 in the form of a beam splitter cube. Here, the central ray 114 runs along the negative z-axis.

(66) While the second central ray 121 running along the x-axis from the beam splitter 101 is deflected, the first central ray 120 is not deflected and runs further along with the negative z-axis downwards in the direction of the first ray deflection element 171 in the first interferometer arm 150.

(67) As the incident plane 154 is spanned by the first central ray 120 and the second central ray 121 directly after the beam splitter 101, the incident plane 154 in the x-z plane, is therefore perpendicular to the x-y plane.

(68) In the first interferometer arm 150, the first central ray 120 runsafter the reflection from the first ray deflection element 171along the positive z-axis and the negative x-axis to then strike the second ray deflection element 172, which stands in the y-z plane at the same position as the first ray deflection element 181 in the second interferometer arm 152.

(69) After the reflection at the second ray deflection element 172, the first central ray 120 strikes an overlap device 106 acting as a beam splitter, which is located next to beam splitter cube of the beam splitter 101. The first central ray 120 is deflected by the overlap device 106 onto the detection plane 131 in the direction of the positive y-axis.

(70) The second central ray 121 is deflected after the beam splitter 101 along the x-axis onto the first ray deflection element 181 of the second interferometer arm 152. After the reflection at the first ray deflection element 181, the second central ray 121 runs along the negative y-axis and the negative x-axis till it strikes the second ray deflection element 182 whose center is located in the x-z-plane at the same position as the central image point 133 of the detection plane 131. After the reflection at the second ray deflection element 182, the second central ray 121 is deflected onto the overlap device 106, through which it passes undeflected to strike the detection plane 131.

(71) The following distances on the central ray relative to the central object point are the same for this object point. The distance from beam splitter 101 to the first ray deflection element 181 is the same as the distance from the second ray deflection element 172 to the overlap device 106. The distances between the first ray deflection elements 171, 181 and the respective second ray deflection elements 172, 182 are the same. The distance between beam splitter 101 and the first ray deflection element 171 is the same as the distance between the second ray deflection element 182 and the overlap device 106.

(72) The exit plane 155 is spanned by the first central ray 120 and the second central ray 121 directly before the overlap device 106 and lies in the x-y plane. With that, the exit plane 155 stands perpendicular to the incident plane 154.

(73) The embodiment of FIG. 8 also has a total of six ray deflections for both interferometer arms 150, 152. Here also, the two beam splitter cubes of the beam splitter 101 and of the overlap device 106 have one ray deflection each. The remaining four ray deflections are achieved, as in the embodiment of FIG. 7, by the first ray deflection element 171 and the second ray deflection element 172 in the first interferometer arm 150 and the first ray deflection element 181 and the second ray deflection element 182 in the second interferometer arm 152.

(74) FIG. 9 shows a schematic of an embodiment of an invention-related interferometer with a monolithic structure.

(75) As the existing embodiment of FIG. 9 with its monolithic optics is difficult to represent three-dimensionally, a section in the x-y plane is shown in FIG. 9a and a section perpendicular to it in the x-z plane is shown in FIG. 9b.

(76) It is to be noted here that the arrangement of the beam splitter cube of the beam splitter 101 and the overlap device 106 and the arrangement of the first central ray 120 and of the second central ray 121 are exactly as in the embodiment of FIG. 8. To understand how the embodiment of FIG. 9 is constructed, it helps to recall the embodiment of FIG. 8.

(77) The beam splitter cube of the beam splitter 101 and the overlap device 106 are indicated by dashed lines, wherein the limiting surfaces are integrated into the monolithic optics; they have however no optical effect. Optically effective are the partially mirrored inner surfaces 212 and 214 of the monolithic optics 210.

(78) Therefore, in the embodiment of FIG. 9, just as in the external form of FIG. 8, the incident plane 154 is in the x-z plane and the exit plane 155 is in the x-y plane perpendicular to it.

(79) For reasons of clarity, the object 110 with the object point 112 are not drawn in FIG. 9. The central ray 114 emanating from the object point 112 can however be identified, which strikes the beam splitter 101 that is implemented as a beam splitter cube.

(80) The first central ray 120 results from the central ray 114, in that it runs without deflection through the beam splitter 101 and along the negative z-axis (see FIG. 9b), till it is reflected at a part of the monolithic optics 210, which is designated as the first ray deflection element 171. After the reflection, the first central ray 120 in turn strikes a part of the monolithic optics 210, which is designated as the second ray deflection element 172. On this path, the first central ray 120 passes through the partially mirrored inner surface 214. From there, the first centra ray 120 is deflected to the overlap device 106 where it is deflected in the direction of the detection plane 131 (see FIG. 9a).

(81) The second central ray 121 results from the central ray 114 by reflection at the beam splitter 101 in the direction of a part of the monolithic optics 210, which is designated as first ray deflection element 181 of the second interferometer arm 152 (see FIG. 9a). On this path, the second central ray 121 passes through the partially mirrored inner surface 212. From there, the second central ray 121 is reflected to another part of the monolithic optics 210, which is designated as second ray deflection element 182. From there, in turn, the second central ray 121 is reflected to the overlap device 106, where it passes through, undeflected, to strike the detection plane 131.

(82) The ray blocker 216 prevents light from the first interferometer arm 150 reaching the second interferometer arm 152.

LIST OF REFERENCE NUMBERS

(83) 100 Three-dimensional interferometer

(84) 101 Beam splitter

(85) 106 Overlap device

(86) 110 Object

(87) 112 Object point

(88) 114 Central ray

(89) 115 Light ray of the beam 140, which is not the central ray 114

(90) 116 Third light ray

(91) 117 Fourth light ray

(92) 120 First central ray

(93) 121 Second central ray

(94) 125 First light ray

(95) 126 Second light ray

(96) 130 Detector

(97) 131 Detection plane

(98) 132 Interference area

(99) 133 Central image point

(100) 134 Image point

(101) 135 Image point which is not image point 133

(102) 150 First interferometer arm

(103) 152 Second interferometer arm

(104) 154 Incident plane

(105) 155 Exit plane

(106) 171 First ray deflection element in the first interferometer arm

(107) 172 Second ray deflection element in the first interferometer arm

(108) 181 First ray deflection element in the second interferometer arm

(109) 182 Second ray deflection element in the second interferometer arm

(110) 192 Diffraction grating

(111) 200 Field distribution of the first electric field on the detection plane

(112) 202 Field distribution of the transformed first electric field on the detection plane

(113) 204 Field distribution of the second electric field on the detection plane

(114) 210 Monolithic optics

(115) 212 Partially mirrored inner surface

(116) 214 Partially mirrored inner surface

(117) 216 Ray blocker

(118) E1.sub.ij First electric field

(119) E2.sub.ij Second electric field

(120) IF Interference term

(121) (i, j) Pixel grid

(122) (m, n) Pixel grid

(123) E2.sub.ij Complex conjugated number of the complex second electric field E2.sub.ij

(124) .sub.ij Phase difference

(125) 1.sub.ij Phase of the first electric field

(126) 2.sub.ij Phase of the second electric field

(127) U Propagation matrix

(128) U.sub.mn,ij Elements of the propagation matrix U