Optical component and wavefront analyser comprising such an optical component

Abstract

The invention relates to an optical component (1) comprising a diffraction grating and an array of hexagonal microlenses that are angularly offset from one another by 10° to 50°. Such an optical component is particularly suitable for use in a wavefront analyser. The wavefront analyser can have two alternate configurations, wherein a distance between the optical component and an image sensor is close to f / 2 or to 3·f / 2, where f is a focal length of the microlenses (11). Such a wavefront analyser can be compact, easy to use and compatible with a wide range of wavelength values for electromagnetic radiation to be analysed.

Description

Description Title: OPTICAL COMPONENT AND WAVE SURFACE ANALYZER COMPRISING SUCH AN OPTICAL COMPONENT Technical field

[0001] The present disclosure relates to an optical component which is suitable for use in a wave surface analyzer. It also relates to the wave surface analyzer, as well as to a method for analyzing an electromagnetic radiation wave surface which uses this analyzer. Prior art

[0002] Many applications require characterizing the shape of an electromagnetic radiation wave surface. One such application involves combining elementary beams of radiation from separate light sources to obtain a final beam whose power is higher, or much higher, than that of each elementary beam produced individually by one of the light sources. Another application is the height and tilt adjustment of separate and juxtaposed mirror segments to form a large mirror that is free of height jumps and slope discontinuities between neighboring segments.

[0003] Throughout this description, the term "wave surface" or "wavefront" of electromagnetic radiation is understood to mean a surface, most often continuous, in which the phase of the electric field of a spectral component of the radiation is constant. A device that is capable of providing information on the local shape of a wave surface is called a wave surface analyzer, or sometimes a wave front analyzer.

[0004] So-called Shack-Hartmann wave surface analyzers have been known for a long time. They use an array of juxtaposed and identical microlenses that is arranged in the radiation propagation path, so that each microlens focuses the radiation in a direction that is locally perpendicular to the wave surface, in accordance with the orientation that the wave surface has at that microlens. Variable local inclinations of the wave surface that exist at the array of Microlenses cause displacements of image points at which the radiation is focused by the microlenses, within a focal plane that is common to all microlenses. These focusing points, also called convergence points, are captured in an image using an image sensor, and their positions directly indicate the inclination of the wave surface that exists at each microlens. In such a use, a Shack-Hartmann wave surface analyzer therefore only provides information on the local tilt of the part of the wave surface that passes through each microlens.

[0005] Document WO 2016 / 042161 A1 , in the name of the applicant of the present patent application, describes another wave surface analyzer whose principle is different from that of Shack-Hartmann. This other analyzer comprises a mask with separate openings and a diffraction grating which is arranged downstream of the openings of the mask. The diffraction grating divides each beam of incident radiation which has passed through one of the openings of the mask into several sub-beams, then superimposing sub-beams which come from openings of the mask which are neighboring. Each superposition of sub-beams forms an interference pattern, called an interferogram. This interferogram is made up of parallel fringes whose orientation depends on the difference in inclination of the wave surface which exists between the openings from which the sub-beams come. The value of the interfringe makes it possible to determine this difference in inclination, commonly called tilt difference.At the same time, a transverse shift that affects the central fringe of the interferogram makes it possible to determine a wave surface advancement gap, commonly called piston gap, which exists between the apertures from which the sub-beams originate. The interferograms are captured using an image sensor, preferably of the matrix image sensor type, which is arranged so that all the interferograms appear on its photosensitive surface. In the wave surface analyzer of WO 2016 / 042161 A1, the diffraction grating has a beam splitter function, to generate the sub-beams which are then superimposed two by two to form the interferograms. The aperture mask makes it possible to limit each sub-beam transversely, so that two interferograms which are neighbors on the image sensor do not overlap.

[0006] An advantage of the WO 2016 / 042161 A1 wave surface analyzer over Shack-Hartmann analyzers is that it provides direct access to the values piston deviations. Indeed, using a S hack-Hartmann wave surface analyzer with microlens array, the tilt deviation values ​​of the wave surface are deduced from the displacements of the focusing points, then the piston deviation values ​​are calculated by interpolation and integration from the tilt deviation values. This results in a significant uncertainty on each piston deviation value which is calculated from measurements carried out using a S hack-Hartmann analyzer, because of the more or less significant curvatures that the wave surface can have locally.

[0007] But, in the wave surface analyzer of WO 2016 / 042161 A1, the opaque parts of the mask, between its openings, cause a significant loss of area in the wave surface to be analyzed. This loss of area causes the following two disadvantages: - a loss of light intensity in the interferograms, which is troublesome when the electromagnetic radiation to be analyzed has a limited or low intensity; and - the piston deviation and tilt deviation values ​​obtained relate to local parts of the wave surface which are reduced, and which are separated from each other with intermediate bands which do not contribute to the piston deviation and tilt values ​​obtained. Technical problem

[0008] From this situation, an aim of the present invention is to propose an improvement of the wave surface analyzer of WO 2016 / 042161 A1, to eliminate or reduce the drawbacks which have just been cited.

[0009] Another object of the invention is to provide wave surface analyzers which are compact, easy to use and each compatible with a wide range of wavelength values ​​for the radiation to be analyzed.

[0010] In particular, the invention aims to provide a new optical component which is specially adapted to form part of an improved wave surface analyzer. Summary of the invention

[0011] To achieve at least one of these aims or another, a first aspect of the invention provides an optical component which comprises: - a diffraction grating, which is hexagonal and has a repetition pitch of a diffracting pattern along three axes of symmetry of the diffraction grating; and - a microlens array, which is also hexagonal, consists of identical converging microlenses, and has a microlens pitch along three axes of symmetry of the microlens array.

[0012] The optical component of the invention is arranged such that the diffraction grating is superimposed on the microlens array in a plane called the superposition plane, or such that an image of the diffraction grating is superimposed on the microlens array in the superposition plane. Furthermore, the diffraction grating and the microlens array are oriented such that in the superposition plane, each axis of symmetry of the diffraction grating, or an image of each axis of symmetry of the diffraction grating, is angularly offset from one of the axes of symmetry of the microlens array by an angle that is between 10° (degree) and 50°.In other words, any axis of symmetry of the diffraction grating, or the image of any axis of symmetry of the diffraction grating, forms with any axis of symmetry of the microlens array, within the superposition plane, an angle which is between 10° + n-60° and 50° + n-60°, where n is an integer between -6 and +6. Preferably, each axis of symmetry of the diffraction grating, or its image, forms with one of the axes of symmetry of the microlens array, an angle which is substantially equal to 30°. It then forms with any axis of symmetry of the microlens array, an angle which is substantially equal to 30° + n-60°, where n has the same meaning as previously.

[0013] According to an additional characteristic of the optical component of the invention, a quotient of the pitch of the microlenses over the repetition pitch of the diffracting pattern, or over a repetition pitch of an image of the diffracting pattern in the superposition plane, is between 2 and 18, the values ​​2 and 18 being inclusive.

[0014] When placed in a beam of electromagnetic radiation, preferably substantially perpendicular to a mean direction of propagation of this radiation, the optical component of the invention divides each part of the beam which passes through one of the microlenses in at least six sub-beams, each of which interferes with a sub-beam that comes from a neighboring microlens, the interference occurring downstream of the superposition plane relative to the radiation propagation direction. The sampling of the wave surface for the piston deviation and tilt deviation values ​​is produced by the microlens array, so that a minimal part of the wave surface is incident on separation spaces that could exist between the microlenses. This sampling can then be particularly dense, especially when the microlenses are contiguous between neighbors and their individual size is small.

[0015] Furthermore, all the light energy of the radiation to be analyzed can be used to characterize the shape of its wave surface when the microlenses have a filling rate of 100% in this wave surface. In other words, it can be particularly advantageous if the microlenses each have a peripheral shape and a size parallel to the superposition plane which are such that the microlens array constitutes a tiling in this superposition plane. Preferably, each microlens can thus have a hexagonal peripheral shape.

[0016] The additional feature of the optical component of the invention, according to which the quotient of the pitch of the microlenses to the repetition pitch of the diffracting pattern, or to the repetition pitch of an image of the diffracting pattern in the superposition plane, is between 2 and 18, ensures that the interferences of the pairs of sub-beams produce numbers of fringes which are suitable to allow the piston deviation and tilt values ​​to be determined with satisfactory precision.

[0017] In preferred embodiments of the optical component of the invention, the diffraction grating may be carried by the microlens array. In particular, the diffraction grating may be etched or printed on the microlens array or on a transparent film, or on a rigid transparent substrate, this film or substrate being bonded to the microlens array. Alternatively, the diffraction grating may be inscribed, in particular by photoinscription, in the microlens array or in a transparent film or rigid transparent substrate which is bonded to the microlens array. embodiments of the photoinscription diffraction grating may in particular be appropriate when this diffraction grating is of the diffracting phase grating type.

[0018] In other possible embodiments of the optical component of the invention, at least one of the diffraction grating and the microlens array may be produced by means of a spatial light modulator. Such a spatial light modulator may be of the spatial phase modulator type. Possibly also, the two diffraction gratings and microlens arrays may be produced together by means of the same spatial light modulator, in particular by using a single modulator of the spatial phase modulator type.

[0019] The optical component of the first aspect of the invention is suitable for forming part of an interference wave surface analyzer, while being able to be supplied separately from other components of such an analyzer. In this case, at least one indication of use for forming an interference wave surface analyzer can be provided with the optical component, in particular in a notice which is attached to this component or via an internet link when the indication of use is provided in dematerialized form.This indication may include a wavelength value λ which is prescribed for a beam of electromagnetic radiation to be analyzed which is intended to pass through the optical component when used in an interference wavefront analyzer, the optical component producing during this use, interference between sub-beams which emerge from the diffraction grating and which have passed through neighboring microlenses in the microlens array. Then, when such a prescribed wavelength value indication is provided, the optical component may have one of the following two dimensional characteristics:. - according to a first possibility, the repetition step of the diffracting pattern, or the repetition step of the image of the diffracting pattern in the superposition plane, is between Δ-f / (2- 3 1 / 2 - pi 1 ) and 4-À-f / (3 1 / 2- pi 1 ), that is, between approximately 0.29- Af / pi 1 and 2.31 -À-f / pn , where f is a focal length of each microlens and pu is the pitch of these microlenses, so that the interferences exist in a plane which is parallel to the superposition plane and distant from this superposition plane by f / 2. For this reason, an interference wave surface analyzer which is obtained according to this first possibility is said to have an f / 2 configuration; or - according to a second possibility, the repetition step of the diffracting pattern, or the repetition step of the image of the diffracting pattern in the superposition plane, is between 4-À-f / (3 1 / 2 -pn) and 8-3 1 / 2-At-f / pii , that is, between approximately 2.31 -Af / pn and 13.86- Af / pn , where f is again the focal length of each microlens and pu the pitch of these microlenses, so that the interferences exist in another plane which is parallel to the superposition plane and distant from this superposition plane by 3-f / 2. For this reason, another interference wave surface analyzer which is obtained according to this second possibility, alternative to the first possibility but from the same optical component, is said to have a 3-f / 2 configuration.

[0020] These two configurations f / 2 and 3-f / 2 allow optimal use of the photosensitive surface of a wave surface analyzer image sensor, by reducing unused areas of this photosensitive surface and while avoiding overlaps between neighboring interferograms. For the f / 2 configuration, the optimal value for the repetition pitch of the diffracting pattern and the prescribed value of wavelength λ are related by the following nominal relationship: pi2 = 2 Af / (3 1 / 2 - pu ), where pi2 denotes the repetition pitch of the diffracting pattern along the symmetry axes of the diffraction grating in the superposition plane, and pu denotes the pitch of the microlenses along the symmetry axes of the microlens array. For the 3-f / 2 configuration, the nominal relationship is: pi2 = 2-3 1 / 2-Af / pii . But an advantage of a wave surface analyzer which is made from an optical component according to the invention is that it can be used even when the wavelength of the radiation to be analyzed differs significantly from the prescribed value λ as resulting from the nominal relationships.

[0021] The prescribed wavelength value À, for the use of the optical component in an interference wave surface analyzer, may belong to the visible range, between 0.36 pm (micrometer) and 0.8 pm, or in the infrared range, between 0.8 pm and 20 pm, or in the terahertz range, between 20 pm and 3 mm (millimeter), or in the ultraviolet range, between 124 nm (nanometer) and 0.36 pm, or in the extreme ultraviolet range, designated by EUV and between 10 nm and 124 nm, or even in the X-ray range, with wavelength values ​​below 10 nm.

[0022] When such an indication of prescribed value λ is provided with the optical component, its diffracting pattern may advantageously be adapted to produce, on a spectral component of the radiation beam to be analyzed which has the prescribed value λ as wavelength value, a phase shift which is substantially equal to + / -pi (TT) radians, between two complementary zones inside the diffracting pattern and for a beam propagation direction which is perpendicular to the superposition plane. This phase shift may be produced by a local increase or a local reduction in the optical thickness of the diffraction grating in one of the two zones relative to the other inside the diffracting pattern. Advantageously, when the pitch of the diffraction grating, denoted pi2, is equal to 2 -λ-f / (3 1 / 2- pi 1 ) and that the optical component is intended to be used in a wave surface analyzer of configuration f / 2, or when the pitch of the diffraction grating p-12 is equal to 2-3 1 / 2 -At-f / pn and the optical component is intended for use in a 3-f / 2 configuration waveface analyzer, one of the two complementary areas within the diffracting pattern may be a disk of diameter substantially equal to 7.66-pi2-3 1 / 2 / (6-n). Such a diffraction pattern reduces additional superpositions that could occur in each interferogram, with sub-beams coming from microlenses of rank i+3 when this interferogram corresponds to the superposition of sub-beams coming from microlenses of rank i and i+1, i being an integer numbering index of the microlenses that are successively located along one of the symmetry axes of the microlens array. The analysis of the interferogram to obtain the piston deviation value and / or those of tilt deviations is then facilitated and more precise.

[0023] A second aspect of the invention provides an interference wave surface analyzer, which comprises: - an optical component which conforms to the first aspect above; - an image sensor, which has a flat photosensitive surface and which is arranged such that this photosensitive surface is parallel to the superposition plane of the optical component, so that interferograms produced on the photosensitive surface by a beam of electromagnetic radiation to be analyzed which passes through the optical component in the direction of the image sensor when using the wave surface analyzer, are captured by the image sensor; and - optionally to provide automated operation for analyzing interferograms, a processing module, adapted to determine piston deviation values, and possibly also tilt deviation values, which exist at the level of the superposition plane in a wave surface of the radiation beam to be analyzed, from the interferograms captured by the image sensor.

[0024] Such a wave surface analyzer may be simple and compact. In particular, its optical part may be limited to the optical component of the first aspect of the invention and the image sensor. Furthermore, the optical component and the image sensor may be provided separately, and combined in accordance with indications provided with the optical component to form the wave surface analyzer.

[0025] When used, the processing module may be adapted to derive a value for the piston gap existing in the wave surface between two areas of this wave surface which are superimposed on neighboring microlenses, from a transverse fringe shift existing in one of the interferograms which corresponds to these two microlenses. It may further be adapted to derive values ​​of tilt gaps which exist between the two areas of the wave surface from a fringe orientation and an interfringe pitch, respectively, existing in the interferogram which corresponds to the two microlenses.

[0026] Advantageously, the prescribed wavelength value λ is provided with the optical component and the repetition pitch of the diffracting pattern belongs to one of the respective intervals mentioned above for the f / 2 configuration and for the 3-f / 2 configuration of the wave surface analyzer. Then, when this repetition pitch of the diffracting pattern is in the interval which corresponds to the f / 2 configuration, a separation distance between the superposition plane and the photosensitive surface of the image sensor can be between f / 8 and 5-f / 8. When the repetition pitch of the diffracting pattern is alternatively in the interval which corresponds to the 3-f / 2 configuration, the separation distance between the superposition plane and the photosensitive surface of the image sensor can be between 5- f / 4 and 15-f / 8.

[0027] When the prescribed wavelength value A is between 0.36 pm and 20 pm, that is, it belongs to the visible range or the infrared range at excluding the Terahertz domain, the microlens array and the photosensitive surface of the image sensor may be separated by a distance that is less than 5 cm (centimeter), preferably between 1 mm and 30 mm.

[0028] Advantageously, to allow easy use of the wave surface analyzer, it may further comprise a mount in which the microlens array and the diffraction grating, together forming the optical component, are rigidly assembled with the image sensor.

[0029] Finally, a third aspect of the invention provides a method for analyzing a wave surface of a beam of electromagnetic radiation, which comprises the following steps: - provide an optical component which conforms to the first aspect of the invention; - direct the radiation beam through the optical component; - arranging an image sensor downstream of the optical component relative to a direction of propagation of the radiation beam, such that a photosensitive surface of the image sensor intersects volumes of superposition of sub-beams which are produced by the optical component from the radiation beam; - activate the image sensor so as to capture interferograms; and - from the captured interferograms, determine piston deviation values, and optionally also tilt deviation values, which exist at the level of the superposition plane in the wave surface of the radiation beam.

[0030] When the prescribed wavelength value λ is provided with the optical component and when the repetition pitch of the diffracting pattern belongs to one of the respective intervals mentioned above for the f / 2 configuration and for the 3-f / 2 configuration of the wave surface analyzer, the method may comprise an initial step in which one of a source assembly of the radiation beam to be analyzed and the optical component is selected relative to the other so that a wavelength value of the source assembly is close to the prescribed value λ of the optical component, so as to produce the interferograms. Indeed, an optical component according to the invention can be used for radiation to be analyzed whose wavelength is substantially different from the prescribed value λ of the optical component. The image sensor is then arranged downstream of the optical component for forming a wavefront analyzer that has the f / 2 configuration or the 3-f / 2 configuration. For example, an optical component with a prescribed value λ of 633 nm can be used for radiation to be analyzed whose wavelength is equal to 612 nm, and an optical component with a prescribed value λ of 1 pm can be used for radiation to be analyzed whose wavelength is equal to 1.5 pm. Optimally, the source assembly is such that the radiation it produces has a non-zero intensity spectral component for the value λ of wavelength that is prescribed for the optical component.

[0031] In first possible uses of the method of the invention, parts of the radiation beam which pass through different microlenses are produced by respective separate sources, in particular by separate fiber sources, and more particularly by separate fiber laser sources, in continuous or pulsed emission regime. These first uses may have the objective of superimposing or juxtaposing in a final beam, elementary beams of radiation which are produced respectively by the separate sources, with respective phases of the elementary beams which coincide so that the final beam has maximum power.The wave surface analyzer of the invention makes it possible to measure piston and / or tilt deviations which exist between elementary beams which are directed to pass through neighboring microlenses, so that the phase shifts which result from these piston and / or tilt deviations are compensated by an appropriate system.

[0032] In second possible uses of the method of the invention, the radiation is reflected simultaneously by juxtaposed segments of a mirror. Then, for each segment of the mirror, a portion of the radiation that is reflected by this segment of the mirror passes through one of the microlenses according to a one-to-one correspondence between the segments of the mirror and the microlenses. For these second uses, the method further comprises calculating height and inclination differences that exist between two neighboring segments of the mirror, from the values ​​of the piston and tilt differences that have been determined. Brief description of the figures

[0033] The characteristics and advantages of the present invention will appear more clearly in the detailed description below of non-limiting exemplary embodiments, with reference to the appended figures among which:

[0034] [Fig. 1] is a plan view of an optical component according to the invention;

[0035] [Fig. 2] illustrates wave surface parameters that can be determined using a wave surface analyzer according to the invention;

[0036] [Fig. 3a] is a longitudinal sectional view of a first wave surface analyzer which is in accordance with the invention, and said to have an f / 2 configuration;

[0037] [Fig. 3b] corresponds to [Fig. 3a] for a second wave surface analyzer which is also in accordance with the invention, and said to have a 3-f / 2 configuration;

[0038] [Fig. 4a] illustrates the principle of formation of an interferogram by a wave surface analyzer which is in accordance with the invention;

[0039] [Fig. 4b] reproduces an example of an image which is captured by a wave surface analyzer according to the invention;

[0040] [Fig. 5a] illustrates a first use of a wave surface analyzer according to the invention, for adjusting elementary beams of electromagnetic radiation which are produced by several separate laser sources; and

[0041] [Fig. 5b] illustrates a second use of a wave surface analyzer according to the invention, for adjusting positions of separate segments of a Keck-type telescope mirror. Detailed description of the invention

[0042] For the sake of clarity, the dimensions of the elements shown in these figures do not correspond to actual dimensions or to actual dimensional ratios. In addition, some of these elements are represented only symbolically, and identical references indicated in different figures designate identical elements or those having identical functions.

[0043] [Fig. 1] shows in superposition a diffraction grating and a part of a microlens array which together constitute an optical component 1 as proposed by the present invention. The microlenses are all identical, convergent, and juxtaposed according to a first hexagonal array. The representation of this microlens array is limited to seven microlenses in [Fig. 1 ], for the sake of clarity of this figure. Each microlens is individually designated by the reference 1 1 , and has a diameter du and a focal length f. The references An designate the axes of symmetry of the microlens array 11 , which are offset by + / -60 0from one axis An to the other. The microlenses 1 1 are juxtaposed parallel to the axes of symmetry An to form their hexagonal network. The juxtaposition pitch of the microlenses 1 1 parallel to each of the axes of symmetry An is noted pu. In the example shown, it is equal to the diameter of the microlenses, so that two microlenses 1 1 which are neighbors are contiguous with a single point of contact between them in the plane of the microlens network. However, the diameter of the microlenses can be less than their juxtaposition pitch pu, or each microlens 1 1 can occupy an entire hexagonal cell of their network.

[0044] The diffraction grating is also hexagonal and consists of repetitions of a diffracting pattern parallel to the A12 axes of symmetry of this diffraction grating. The A12 axes of symmetry of the diffraction grating are therefore also offset by + / -60 0from one axis of symmetry A12 to the other. The diffracting pattern has an outline in the shape of a regular hexagon, as shown in broken lines in the local magnification insert of the figure. This diffracting pattern can be divided into two complementary zones Z1 and Z2, zone Z1 having the shape of a disc 12 of diameter di2, which is centered in the pattern. In the case of a diffraction grating of the phase grating type, the diffracting pattern can be characterized by a first optical thickness inside the disc 12, that is to say in zone Z1, and by a second optical thickness, which is different from the first, in zone Z2. For example, the diffraction grating can be formed by a plate of a transparent material, with faces which are initially parallel, and in which holes with flat bottoms have been formed at the locations of zones Z1.In this way, the diffraction grating has an optical thickness that is reduced in the Z1 areas relative to the Z2 areas. Alternatively, each disc 12 may be raised relative to the Z2 areas that are intermediate between the discs 12, so that the diffraction grating has an optical thickness that is increased in the Z1 areas relative to the Z2 areas. Such a diffraction grating with the discs 12 that are raised may be formed by etching. selective, by masking the zones Z1. Other embodiments are still possible for the diffraction grating, some of which have been cited in the general part of this description. p-12 denotes the repetition pitch of the diffracting pattern parallel to the axes of symmetry A12. In a known manner, the phase shift which is produced by a hole or a relief formed in the plate of transparent material which constitutes the diffraction grating, is: Acp = 2-TT-(n-1 )-h / À, where h is the depth of the hole or the height of the relief, À is the wavelength of the radiation, and n is the refractive index of the transparent material. This phase shift Acp is a phase advance in the case of a hole and a phase delay in the case of a relief. In possible embodiments, the value of the depth or height h can be selected so that Acp = ±TT.

[0045] For the embodiment of the invention described here by way of example, the diffraction grating and the microlens array are arranged against each other, so that they can be considered as being superimposed in a common plane, called the superposition plane and denoted PS. In addition, they are oriented relative to each other so that each axis of symmetry An of the microlens array 1 1 is angularly offset by 30° relative to one of the axes of symmetry A12 of the diffraction grating. In addition, again for the embodiment described here by way of example, the pitch pu of the microlens array 1 1 is equal to approximately 12 times the pitch p-12 of repetition of the diffracting pattern. x and y denote two Cartesian axes perpendicular to each other which are contained in the superposition plane PS. In the following, z denotes a third Cartesian axis which is perpendicular to both the x and y axes.

[0046] For electromagnetic radiation that propagates substantially parallel to the z-axis, a wave surface of this radiation that exists at the superposition plane PS is designated by S in the following. The wave surface S may have a local advancement along the z-axis that varies between different points of this wave surface. In [Fig. 2], zi is thus the local advancement of a part S1 of the wave surface S, and Z2 is the local advancement of another part S2 of the wave surface S. The advancement gap of the wave surface S between its parts S1 and S2 is then AP = zi - Z2, and is called the piston gap that exists between these two wave surface parts. Piston gap values ​​AP will be determined using the invention, between parts of the wave surface S that are superimposed on neighboring microlenses 1 1 within the optical component 1 .

[0047] In addition to its local advancement parallel to the z axis which can be variable, the wave surface S can have a local inclination which is also variable. Thus, the wave surface part S1 can form an angle txi with a projection of the x axis in a first cutting plane which is parallel to the x and z axes, and simultaneously form another angle t yi with a projection of the y-axis into a second section plane parallel to the y- and z-axes. Similarly, an inclination of the wave surface portion S2 can be characterized by the angles tx2 and ty2, which are defined in the same way as txi and t yi of the wave surface part S1. Then, the inclination difference between the parts S1 and S2 of the wave surface S can be characterized by the difference values ​​Atx = txi - tx2 and At y = t yi - t y2, which are commonly referred to as tilt and tip deviation values, respectively, between the wave surface portions S1 and S2. Such tilt and tip deviation values ​​can be determined using the invention, between the portions of the wave surface S that are superimposed on neighboring microlenses 11 within the optical component 1. For an optical component with hexagonal symmetry as considered in the present description, and when this optical component is used in a wave surface analyzer, a tilt variation as well as a tip variation, which affects a wave surface portion superimposed on only one of the microlenses, modifies both an interfringe pitch value and an orientation of the fringes in the interferograms in which the sub-beams that have passed through this microlens participate. For this reason, tilt deviation values ​​are understood to mean the differences Atx but also those At y, without distinction, throughout this description.

[0048] In [Fig. 3a], F denotes the electromagnetic radiation beam that is incident on the optical component 1 , and SF-i, SFo and SF+i denote three sub-beams that are produced by the diffraction grating of the optical component 1 from the beam F for each of the microlenses 1 1 . Due to the microlenses 1 1 , all the sub-beams SF-i, SFo and SF+1 converge in the common focal plane of the microlenses, denoted PF, at separate points. The focal plane PF is parallel to the superposition plane PS and distant from it by the focal length f. A sub-beam SFo corresponding to diffraction order 0, three other sub-beams SF-i each corresponding to a diffraction order -1, and three additional sub-beams SF+i each corresponding to a diffraction order +1 then come from each microlens 1 1 .If the wave surface S is parallel to the xy plane at this microlens 1 1 , these seven sub-beams converge at points of the. focal plane PF which are located at the vertices and center of a regular hexagon whose center is aligned with that of the microlens parallel to the z axis: the sub-beam SFo converges at the center of the hexagon, and the six sub-beams SF-i and SF+i converge at its vertices. Due to the diffraction directions, the x axis as appearing in [Fig. 3a] is perpendicular to one of the axes of symmetry A12 of the diffraction grating. It is also parallel to one of the axes of symmetry An of the array of microlenses 1 1 .

[0049] For a first configuration of a wave surface analyzer 10 according to the invention, called configuration f / 2, the pitch P12 of repetition of the diffracting pattern along each axis A12 of the diffraction grating is such that the point of convergence of each sub-beam SF-1 or SF+1 which comes from a microlens 1 1 is substantially superimposed, in the focal plane PF, on the point of convergence of the sub-beam SFo which comes from a neighboring microlens, as appears in [Fig. 3a]. For this, the pitch P12 of repetition of the diffracting pattern along the axes A12, and the pitch pu of the microlenses 1 1 along the axes An, verify the nominal relation: P12 = 2-À-f / (3 1 / 2- pi 1 ). Throughout the present description, λ denotes a wavelength value which is prescribed for the optical component 1 , and therefore prescribed for each wave surface analyzer which is made up from this optical component. This prescribed value λ is that to be adopted for the wavelength of the electromagnetic radiation of the beam F, during nominal use of the wave surface analyzer 10. The hatched areas in [Fig. 3a] show the superposition volumes between a sub-beam SF+1 and a sub-beam SF-1 which come from two neighboring microlenses 11. A photodetection plane, which is parallel to the superposition plane PS and which is denoted PD, with which the superposition volumes of the sub-beams have a maximum cross-sectional area, is located at the distance f / 2 from the superposition plane PS, downstream of the latter with respect to the direction of propagation of the radiation beam F.The wave surface analyzer 10 has the f / 2 configuration when it comprises the optical component 1 and an image sensor 2 whose photosensitive surface coincides with the photodetection plane PD, halfway between the superposition plane PS and the focal plane PF. The value f / 2 for the distance between the superposition plane PS and the image sensor 2 is optimal, also called nominal, for the f / 2 configuration of the wave surface analyzer. Inside the photodetection plane PD, the sub-beams SF-1 and SF+1 which come from two neighboring microlenses 1 1 are superimposed in an area. interference areas Al, where they produce an interferogram that is captured by the image sensor 2. [Fig. 4a] schematically illustrates this principle of formation of the interference areas Al for a direction of symmetry axis An. The interference areas Al that are thus obtained are aligned in the photodetection plane PD parallel to the symmetry axes An thanks to the angular offset of 30° between these symmetry axes An and the symmetry axes Ai2. The shape of the peripheral boundary of each interference area Al is altered to a small extent by the positions of the convergence points in the focal plane PF, depending on the local inclinations of the wave surface S at the superposition plane PS.The shape of the peripheral boundary of each interference area Al is also altered when the wavelength of the radiation beam F differs from the prescribed value λ as resulting from the nominal relationship provided above, the repetition pitch pi2 of the diffracting pattern and the pitch pu of the microlens array being intrinsic and fixed parameters for a given optical component. It is further altered when the photosensitive surface of the image sensor 2 is offset from the optimal photodetection plane PD. However, these alterations of the peripheral boundaries of the interference areas do not disturb the content of the interferograms.

[0050] The image sensor 2 is preferably of a matrix type with a pitch of individual photodetector elements, commonly called pixels, in its photosensitive surface that is small enough to provide sufficient sampling of the interferograms within the interference areas Al. [Fig. 4b] shows an image as captured by the sensor 2 during nominal use of the wave surface analyzer 10 of [Fig. 3a], i.e. with the f / 2 configuration. This image therefore corresponds to the illumination that exists in the photodetection plane PD. Each interference area Al contains a separate interferogram, and an indication of the position of the microlenses 1 1 is indicated by superposition, in projection parallel to the z axis.

[0051] The characterization of the shape of the wave surface S, as it exists at the level of the superposition plane PD, is given by the analysis of the interferograms. Each interferogram provides differential information between the positions of the centers of the two microlenses 1 1 from which the two sub-beams SF-i and SF+i that formed this interferogram originate. The light intensity distribution within each interferogram, as captured by the image sensor 2, is given by the formula next: where AP is the piston gap that exists between the parts of the wave surface S that are respectively at the level of one and the other of the two neighboring microlenses, such as this gap AP was introduced above with reference to [Fig. 2], Atx and Aty are the tilt gaps that exist between these parts of the wave surface S, also as they were introduced with reference to [Fig. 2], u is a Cartesian coordinate along an axis in the photodetection plane PD that is parallel to one of the symmetry axes An of the microlens array, k is a sensitivity scale coefficient of the image sensor 2 that is positive and non-zero, and the parameters p-12 and Δ are taken as they were defined above. Thus, the interference state at the center of the interferogram, that is to say for x=y=u=0, provides the value of the piston gap AP.All the piston deviation values ​​AP that are deduced from all the interferograms then provide a basic characterization of the shape of the wave surface S: they are the sagittal height values, along the z axis, of the wave surface S for the sampling mesh that is constituted by the centers of the microlenses 11 . Optionally, the tilt deviation values ​​Atx and Aty can be further deduced from the interferograms, by extracting from each interferogram the orientation of the fringes that constitute it and the corresponding interfringe pitch value. Such an additional analysis of the fringe structures of the interferograms is known to those skilled in the art, so it is not necessary to detail it further here. It provides the inclinations of the planes that are tangent to the wave surface S at the centers of the microlenses 1 1.The deduction of all piston deviation values ​​for the basic characterization of the wave surface, and optionally of all tilt deviation values ​​for its further characterization, can be performed in an automated manner by a processing module 3, denoted CPU in [Fig. 3a] and [Fig. 3b]. Such a processing module 3 can be programmed to first extract the interferograms of each image that is captured by the sensor 2, by associating each interferogram with its position in the image, i.e. its position relative to the microlens array 11, and programmed to then analyze each interferogram separately, in order to deduce the piston deviation value AP and possibly also the tilt deviation values.

[0052] [Fig. 3b] shows an alternative embodiment of a wave surface analyzer which is also in accordance with the invention. The wave surface analyzer 10 of [Fig. 3b] has a 3-f / 2 configuration. For this, the optical component 1 still conforms to the description which was provided with reference to [Fig. 1], but it now satisfies the following new nominal relationship: pi2 = 2-3 1 / 2-À-f / pn . All previously introduced notations relating to the optical component 1 and the radiation to be analyzed, including those relating to the shape of the wave surface S, are retained identically. The hatched areas in [Fig. 3b] correspond to the new superposition volumes of the SF-i and SF+i subbeams that come from neighboring 1 1 microlenses. However, these superposition volumes are now limited downstream to avoid additional superpositions with SFo subbeams. With the new nominal relationship, the pairs of subbeams for which optical component 1 produces superpositions are identical to those in [Fig. 3a], except that these superpositions occur at a distance from the superposition plane PS that is larger than the focal length f.The position of the photodetection plane PD for which the interference areas Al are the maximum, is then at the distance of 3-f / 2 from the superposition plane PS, still downstream of this superposition plane PS with respect to the direction of propagation of the radiation beam F, the two planes PD and PS still being parallel. This new position of the photodetection plane PD corresponds to the optimal, or nominal, position of the image sensor 2 for the 3-f / 2 configuration of the wave surface analyzer 10. The optical operation of the wave surface analyzer 10, and the principle of analysis of the interferograms that it produces, such as these operations and principles have been described for the f / 2 configuration, are identical for the 3-f / 2 configuration. In particular, the formula for the distribution of light intensity within each interferogram is the same for both the f / 2 and 3-f / 2 configurations.

[0053] For the embodiments of the invention which have just been described, it is possible that sub-beams which are produced by the optical component 1, but which are other than those SF-i and SF+i, interfere with the latter within the interference areas Al. These other sub-beams correspond to higher diffraction orders which are generated by the diffraction grating, and they are likely to reduce a contrast of the interferograms and hinder their analysis. When the diffracting pattern is consisting, in the superposition plane PS, of a disc 12 of diameter di2 inside which the diffraction grating produces a phase shift of + / -TT for the radiation beam F (see the description above with reference to [Fig. 1]), it may be advantageous for the diameter di2 to be substantially equal to 7.66-pi2-3 1 / 2 / (6-n), especially for the configuration f / 2 when pi2 = 2-À-f / (3 1 / 2- pu ), or for the 3-f / 2 configuration when pi2 = 2-3 1 / 2 -À-f / pii . Such a sizing of the diffracting pattern reduces or cancels intensities of some of the higher order sub-beams which are likely to reach the Al interference areas.

[0054] [Fig. 5a] shows a first possible use of a wave surface analyzer 10 according to the invention, to produce a coherent combination of elementary light beams which are produced by a set of fiber laser sources 1000. The laser sources 1000 are capable of interfering with each other, and arranged in parallel so that the output sections of the optical fibers 1001, 1002,... are substantially all arranged in the same plane perpendicular to the z axis. Each optical fiber 1001, 1002,... is provided with an output lens 1011, 1012,..., so that the elementary light beam F1, F2,... which comes from this optical fiber is collimated. The number of separate laser sources which thus produce elementary beams in parallel is not limited, and can be for example of the order of several hundred thousand. All elementary beams F1, F2,...which are produced by the laser sources 1000 are brought to be incident on the optical component 1 of the wave surface analyzer 10, substantially parallel to the z axis. Thus, they all together form the radiation beam F as mentioned above. The optical component 1 has at least as many microlenses 1 1 as the number of laser sources 1000, and the transverse distribution of the outputs of the optical fibers 1001, 1002,... constitutes a hexagonal array, to correspond to the arrangement of the microlenses 1 1 in the microlens array. In this way, a single optical fiber is directed towards one of the microlenses 1 1 , which is dedicated to it. The references 101 and 102 designate two converging lenses, with their respective focal lengths denoted fi and f2. They are optionally arranged to form together an afocal optical system which is designated by the reference 100.In other words, the image focus of the lens 101 is superimposed on the object focus of the lens 102. Both lenses 101 and 102 have sufficient transverse extensions to contain all the. elementary beams Fi, F2, ..., so that the afocal optical system 100 has the function of adapting the pitch of the hexagonal network of the outputs of the optical fibers 1001, 1002, ... to the pitch pu of the network of microlenses 1 1. The laser sources 1000 constitute with the afocal optical system 100 the source assembly mentioned in the general part of the present description. The wave surface analyzer 10 can be of f / 2 or 3-f / 2 configuration. Such an implementation makes it possible to determine the piston deviations AP and the tilt deviations which are present between neighboring optical fibers, when all the fibered laser sources 1000 are monochromatic with the same common wavelength which substantially coincides with the prescribed value λ of the wave surface analyzer 10.A particular case of this first use of a wave surface analyzer 10 which is in accordance with the invention is that where the laser sources 1000 are of the pulsed type, each for delivering a very short elementary pulse of radiation, for example of the order of a picosecond or less. Once the piston deviations AP thus measured have been compensated, for example by using a set of phase shifters not shown, the elementary pulses can be superimposed to constitute a single resulting pulse of radiation which has a very high power. The respective directions of propagation of the elementary pulses can also be determined, by using the tilt deviations which exist at the lenses, in order to make them all parallel to each other.

[0055] [Fig. 5b] shows another possible use of a wave surface analyzer according to the invention, for measuring height and inclination differences which may be present between neighboring segments of a Keck-type telescope mirror. Depending on the differences which will be measured in this way, the relative positions of the mirror segments can be readjusted, so that a wave surface produced by reflection on the complete mirror is free of steps or slope discontinuities.

[0056] References 101 and 102 in [Fig. 5b] further designate two converging lenses. They are located inside an analysis path denoted ANA, which leads to the wave surface analyzer 10. A semi-reflecting plate 104 makes it possible to couple this analysis path ANA to an output of the telescope, in addition to an application path denoted APP. The lens 101 is placed in the image of the focal plane of the telescope which is formed by the semi-reflecting plate 104, and the lens 102 is placed downstream of the lens 101, at a distance of the latter which is equal to the focal length of the lens 102. In this way, the lens 102 ensures that the radiation emerging from the telescope is collimated when it reaches the optical component 1 of the wave surface analyzer 10, if possible defects of the telescope are not taken into account or have been corrected. The telescope may consist of a primary mirror 2000 and a secondary mirror 2100. The primary mirror 2000 is constituted by all the juxtaposed mirror segments 2001, 2002, 2003, 2004,... These mirror segments are juxtaposed in a hexagonal array to constitute the primary mirror 2000, in order to use an optical component 1 of the wave surface analyzer as described above. The focal length of the lens 101 is selected so as to form, by means of the secondary mirror 2100 and the two lenses 101 and 102, an image of the primary mirror 2000 on the microlens array of the optical component 1.Furthermore, this optical component 1 is oriented and transversely adjusted in position so that the image of each of the mirror segments 2001, 2002, 2003, 2004,... is superimposed on only one of the microlenses 11. In the example shown, the wave surface analyzer 10 has the f / 2 configuration, but a wave surface analyzer with a 34 / 2 configuration can be used alternatively. The aim of the present application of the invention is to determine the relative positional errors of the individual mirror segments 2001, 2002, 2003, 2004... The radiation which is used for this can come from a star 2200 located at a very great distance from the telescope, and towards which the telescope is turned. Thus, the star 2200, the telescope, the semi-reflecting plate 104 and the lenses 101 and 102 constitute the source assembly within the meaning of the general part of this description.Then, each interferogram makes it possible to determine the piston gap AP that exists between the light beams reflected by two neighboring mirror segments. This piston gap is equal to twice the height gap that exists between these two mirror segments. Each interferogram also makes it possible to calculate the tilt gap that exists between the two mirror segments. The heights of the mirror segments 2001, 2002, 2003, 2004..., and possibly also their tilts, can then be adjusted according to the measurement values ​​that are provided by the processing module 3 for the piston gaps AP, and possibly also for the tilt gaps Atx and Aty, in order to reduce or cancel the height and tilt gaps that are present between neighboring mirror segments.

[0057] It is understood that the invention may be reproduced by modifying secondary aspects of the embodiments which have been described in detail above, while retaining at least some of the advantages cited. In particular, the following modifications may be implemented: - instead of being superimposed on the microlens array, the diffraction grating can be optically conjugated with it, in particular by using an imaging system which is upstream of the microlens array, and adapted to produce an image of the diffracting grating on the microlens array; - the diffraction grating, when it is of the phase grating type, can have more than two discrete phase shift values ​​which are different; - the diffraction grating may be of an amplitude variation type instead of a phase variation type, in particular with more than two discrete amplitude transmission values ​​which are different, thus being able to approach a spatially varying amplitude transmission diffraction grating which is sinusoidal; - the microlenses may not be contiguous with each other in the superposition plane, in particular when their individual diameter is less than their juxtaposition pitch along the axes of symmetry of their network; - the values ​​of the parameters of the optical component, and the distance between the image sensor and the superposition plane in the wave surface analyzer, may differ from the nominal values ​​and relationships that have been cited, while remaining within the ranges specified in the claims. In particular, the wavelength value of the radiation to be analyzed may differ from the value λ that is prescribed for the optical component used as long as the pitch of the diffraction grating is within the range that corresponds to the wavelength of the radiation for the f / 2 or 3-f / 2 configuration used; - an optical component according to the invention can be used in optical systems other than wave surface analyzers; and - a wave surface analyzer according to the invention can be used for applications other than those described with reference to [Fig. 5a] and [Fig. 5b], in particular for producing adaptive or active optics.

Claims

Claims

1. Optical component (1) comprising: - a diffraction grating, hexagonal and having a repetition pitch (p-12) of a diffracting pattern along three axes of symmetry (A12) of the diffraction grating, characterized in that it further comprises: - a microlens array, also hexagonal, consisting of identical converging microlenses (1 1 ), and having a pitch (pu) of the microlenses along three axes of symmetry (An) of the microlens array, the optical component (1 ) being arranged so that the diffraction grating is superimposed on the microlens array in a plane called the superposition plane (PS), or in that an image of the diffraction grating is superimposed on the microlens array in the superposition plane, the diffraction grating and the microlens array being oriented so that in the superposition plane (PS), each axis of symmetry (A12) of the diffraction grating, or an image of each axis of symmetry of the diffraction grating, is angularly offset from one of the axes of symmetry (An) of the microlens array by an angle which is between 10° and 50°, and a quotient of the pitch of the microlenses (pu) on the repetition pitch of the diffracting pattern (p-12),or on a repetition step of an image of the diffracting pattern in the superposition plane (PS), is between 2 and 18, the values ​​2 and 18 being inclusive.,

2. An optical component (1) according to claim 1, wherein an individual size of the microlenses (11) parallel to the superposition plane (PS) is such that any two of the microlenses which are neighbors in the microlens array are contiguous.

3. Optical component (1) according to claim 1 or 2, in which the diffraction grating is carried by the microlens array, in particular engraved or printed on the microlens array or on a transparent film, or on a rigid transparent substrate, said film or substrate being glued to the microlens array, or the diffraction grating is inscribed, in particular by photoinscription, in the microlens array or in a transparent film or rigid transparent substrate which is bonded to the microlens array.

4. Optical component (1) according to any one of the preceding claims, wherein at least one of the diffraction grating and the microlens array (11) is produced by means of a spatial light modulator, preferably both diffraction gratings and microlenses are produced together by means of the same spatial light modulator.

5. An optical component (1) according to any preceding claim, further comprising an indication of a prescribed wavelength value λ of a beam (F) of electromagnetic radiation to be analyzed which is intended to pass through the optical component when using said optical component in an interference wave surface analyzer (10), said optical component producing during said use interference between sub-beams (SF-i, SF+i) which emerge from the diffraction grating and which have passed through neighboring microlenses (11) in the microlens array, the repetition pitch of the diffracting pattern (p-12), or the repetition pitch of the image of the diffracting pattern in the superposition plane (PS), being between λ-f / (2-3 1 / 2 -pn) and 4- À- f / (3 1 / 2- pi 1 ), where f is a focal length of each microlens (11 ) and pu is the pitch of the microlenses, so that the interferences exist in a plane which is parallel to the superposition plane and distant from said superposition plane by f / 2, or the repetition pitch of the diffracting pattern (p-12), or the repetition pitch of the image of the diffracting pattern, in the superposition plane (PS), being between 4-À-f / (3 1 / 2 -pn) and 8-3 1 / 2 -At-f / pii , so that the interferences exist in a plane which is parallel to the superposition plane and distant from said superposition plane by 3-f / 2.

6. Optical component (1) according to claim 5, wherein the diffracting pattern is adapted to produce, on a spectral component of the beam (F) of radiation to be analyzed which has the prescribed value λ as wavelength value, a phase shift which is substantially equal to + / -pi radians, between two complementary zones (Z1, Z2) inside the diffracting pattern and for a direction of propagation of said beam of radiation which is perpendicular to the superposition plane (PS).

7. An interference wave surface analyzer (10), comprising: - an optical component (1) which is in accordance with any one of the preceding claims; and - an image sensor (2), which has a flat photosensitive surface and is arranged such that the photosensitive surface is parallel to the superposition plane (PS) of the optical component (1), so that interferograms produced on said photosensitive surface by a beam (F) of electromagnetic radiation to be analyzed which passes through the optical component in the direction of the image sensor when using the wave surface analyzer (10), are captured by said image sensor.

8. The wave surface analyzer (10) of claim 7, further comprising: - a processing module (3), adapted to determine piston deviation values ​​which exist at the level of the superposition plane (PS) in a wave surface (S) of the radiation beam (F) to be analyzed, from the interferograms captured by said image sensor.

9. Wave surface analyzer (10) according to claim 8, wherein the processing module (3) is adapted to deduce a value for the piston gap existing in the wave surface (S) between two areas of said wave surface which are superimposed on two neighboring microlenses (11), from a transverse fringe shift existing in one of the interferograms which corresponds to said two microlenses.

10. Wave surface analyzer (10) according to claim 9, wherein the processing module (3) is further adapted to deduce tilt deviation values ​​existing between the two zones of the wave surface (S) which are superimposed on the two neighboring microlenses (11), from a fringe orientation and an interfringe pitch, respectively, existing in the interferogram which corresponds to said two microlenses.

11. A wave surface analyzer (10) according to any one of claims 7 to 10, wherein the optical component (1) is according to claim 5 or 6, and a separation distance between the superposition plane (PS) and the surface photosensitive of the image sensor (2) is between f / 8 and 5-f / 8 if the repetition pitch of the diffracting pattern (P12), or the repetition pitch of the image of the diffracting pattern in the superposition plane, is between Δ-f / (2-3 1 / 2 - pi 1 ) and 4-À-f / (3 1 / 2 - pi 1 ), or the separation distance between the superposition plane (PS) and the photosensitive surface of the image sensor (2) is between 5-f / 4 and 15-f / 8 if the repetition pitch of the diffracting pattern (P12), or the repetition pitch of the image of the diffracting pattern in the superposition plane, is between 4-À-f / (3 1 / 2 -pn) and 8-3 1 / 2 -To-f / pn .

12. Method for analyzing a wave surface (S) of a beam (F) of electromagnetic radiation, comprising the following steps: - providing an optical component (1) which conforms to any one of claims 1 to 6; - directing the beam (F) of radiation through the optical component (1); - arranging an image sensor (2) downstream of the optical component (1) relative to a direction of propagation of the radiation beam (F), such that a photosensitive surface of the image sensor intersects volumes of superposition of sub-beams (SF-1, SF+i) which are produced by the optical component from the radiation beam; - activate the image sensor (2) so as to capture interferograms; and - from the captured interferograms, determine piston deviation values ​​that exist at the level of the superposition plane (PS) in the wave surface (S) of the radiation beam (F).

13. A method according to claim 12, wherein the optical component (1) is in accordance with claim 5, and the method comprises an initial step in which one of a source assembly of the radiation beam (F) and the optical component is selected relative to the other such that a wavelength value of the source assembly is close to the prescribed value λ of the optical component, so as to produce the interferograms, and wherein the image sensor (2) is arranged downstream of the optical component (1) to form a wave surface analyzer (10) which is in accordance with claim 11.

14. Method according to claim 12 or 13, according to which parts of the radiation beam (F) which pass through different microlenses (11) are produced. by respective separate sources (1000), in particular by separate fiber sources, and more particularly by separate fiber laser sources.

15. A method according to claim 12 or 13, wherein the radiation is reflected simultaneously by juxtaposed segments (2001, 2002, 2003,...) of a mirror (2000), and for each segment (2001, 2002, 2003,...) of the mirror (2000), a portion of the radiation which is reflected by said segment of the mirror passes through one of the microlenses (11) in a one-to-one correspondence between the segments of the mirror and the microlenses, and the method further comprises: - from the captured interferograms, also determining tilt deviation values ​​which exist at the superposition plane (PS) in the wave surface (S) of the radiation beam (F); and - calculate the height and inclination differences that exist between two segments (2001, 2002, 2003,...) adjacent to the mirror (2000), from the values ​​of the piston and tilt differences that have been determined.

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