OPTICAL COMPONENT AND WAVE SURFACE ANALYZER COMPRISING SUCH AN OPTICAL COMPONENT

Abstract

An optical component (1) comprises a diffraction grating and a microlens array that are hexagonal and angularly offset from each other by 10° to 50°. Such an optical component is particularly well-suited for use in a wavefront analyzer. The wavefront analyzer can alternatively have two configurations, in which the distance between the optical component and an image sensor is close to f / 2 or 3·f / 2, where f is the focal length of the microlenses (11). Such a wavefront analyzer can be compact, easy to use, and compatible with a wide range of wavelength values ​​for the electromagnetic radiation to be analyzed. (Shorthand figure: Figure 1)

Description

Title of the invention: OPTICAL COMPONENT AND WAVE SURFACE ANALYZER COMPRISING SUCH A COMPONENT OPTICAL technical field

[0001] This description relates to an optical component adapted for use in a wavefront analyzer. It also relates to the wavefront analyzer itself, as well as a method for analyzing an electromagnetic radiation wavefront using this analyzer. Previous technique

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

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

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

[0005] Document WO 2016 / 042161 A1, filed on behalf of the applicant of this patent application, describes another wavefront analyzer whose principle differs from that of the Shack-Hartmann analyzer. This other analyzer comprises a mask with separate apertures and a diffraction grating arranged downstream of the mask apertures. The diffraction grating splits each beam of incident radiation that has passed through one of the mask apertures into several subbeams, then superimposes subbeams originating from adjacent mask apertures. Each superposition of subbeams forms an interference pattern, called an interferogram. This interferogram consists of parallel fringes whose orientation depends on the difference in inclination of the wavefront between the apertures from which the subbeams originate. The value of the fringe spacing allows this difference in inclination, commonly called the tilt difference, to be determined.Simultaneously, a transverse shift affecting the central fringe of the interferogram allows the determination of a wavefront advance deviation, commonly called the piston gap, which exists between the apertures from which the subbeams originate. The interferograms are captured using an image sensor, preferably a matrix image sensor, which is positioned so that all the interferograms appear on its photosensitive surface. In the WO 2016 / 042161 Al wavefront analyzer, the diffraction grating has a beam splitter function to generate the subbeams, which are then superimposed in pairs to form the interferograms. The aperture mask limits each subbeam transversely so that two interferograms that are adjacent on the image sensor do not overlap.

[0006] One advantage of the wavefront analyzer of WO 2016 / 042161 Al compared to Shack-Hartmann analyzers is that it provides direct access to piston gap values. Indeed, when using a Shack-Hartmann wavefront analyzer with a microlens array, the wavefront tilt gap values ​​are deduced from the displacements of the focal points, and then the piston gap values ​​are calculated by interpolation and integration from the tilt gap values. This results in a significant uncertainty in each piston gap value calculated from measurements made using a Shack-Hartmann analyzer, due to the varying degrees of curvature that the wavefront may exhibit locally.

[0007] However, in the wavefront analyzer of WO 2016 / 042161 Al, 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 leads to the following two disadvantages: - a loss of light intensity in the interferograms, which is problematic when the electromagnetic radiation to be analyzed has a limited or low intensity; and - the piston gap and tilt gap 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 participate in the piston gap and tilt values ​​obtained. Technical problem

[0008] From this situation, one object of the present invention is to propose an improvement of the wave surface analyzer of WO 2016 / 042161 Al, to eliminate or reduce the disadvantages which have just been mentioned.

[0009] Another object of the invention is to provide wave surface analyzers that 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 that is specially adapted to be used in the construction of an improved wavefront analyzer. Summary of the invention

[0011] To achieve at least one of these goals or another, a first aspect of the invention proposes an optical component which comprises: - a diffraction grating, which is hexagonal and has a repetition rate 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 shifted with respect to one of the axes of symmetry of the microlens array by an angle that is between 10° 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 grating, inside the superposition plane, an angle which is between 10° + n-60° and 50° + n-60°, where n is an integer between . 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 microlensing grating, an angle that is approximately equal to 30°. It then forms with any axis of symmetry of the microlensing grating, an angle that is approximately equal to 30° + n-60°, where n has the same meaning as before.

[0013] According to an additional feature of the optical component of the invention, a quotient of the pitch of the microlenses to the repetition pitch of the diffracting pattern, or to 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 an average direction of propagation of this radiation, the optical component of the invention divides each portion of the beam passing through one of the microlenses into at least six sub-beams, each of which interferes with a sub-beam originating from a neighboring microlens. The interference occurs downstream of the plane of superposition relative to the direction of radiation propagation. The sampling of the wavefront for piston gap and tilt gap values ​​is produced by the microlens array, such that a minimal portion of the wavefront is incident on any separation gaps that might exist between the microlenses. This sampling can then be particularly dense, especially when the microlenses are contiguous and have a small individual size..

[0015] Furthermore, all the light energy of the radiation to be analyzed can be used to characterize the shape of its wavefront when the microlenses have a 100% fill rate in this wavefront. In other words, it can be particularly advantageous for each microlens to have a peripheral shape and size parallel to the superposition plane such that the microlens array forms 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 microlens pitch 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 subbeam pairs produce fringe numbers which are suitable to allow the piston gap and tilt values ​​to be determined with satisfactory accuracy.

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

[0018] In other possible embodiments of the optical component of the invention, at least one of the diffraction grating and the microlensing array can be implemented using a spatial light modulator. Such a spatial light modulator can be of the spatial phase modulator type. Alternatively, both the diffraction grating and the microlensing array can be implemented together using 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 adapted for use in the construction of an interference wavefront analyzer, while also 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 wavefront analyzer may be provided with the optical component, in particular in instructions attached to the component or via an internet link when the indication of use is provided in electronic form.This specification may include a wavelength value X prescribed for a beam of electromagnetic radiation to be analyzed, intended to pass through the optical component when used in an interference wavefront analyzer. During this use, the optical component produces interference between subbeams emerging from the diffraction grating that have passed through adjacent microlenses in the microlens array. Therefore, when such a prescribed wavelength value is provided, the optical component may have one of the following two dimensional characteristics: - According to a first possibility, the repetition rate of the diffracting pattern, or the repetition rate of the image of the diffracting pattern in the superposition plane, is between Xf / (2-31 / 2-pn) and 4-Xf / (31 / 2-pn), that is, between approximately 0.29-Xf / pn and 2.31-Xf / pn, where f is the focal length of each microlens and pu is the spacing of these microlenses, so that the interference exists in a plane that is parallel to the superposition plane and at a distance from this superposition plane of f / 2. For this reason, an interference wavefront analyzer 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 included between 4-Xf / (31 / 2-pn) and 8-31 / 2-Xf / pn, that is, between approximately 2.31-Xf / pii and 13.86-Xf / pib where f is still 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 at a distance from this superposition plane of 3-f / 2. For this reason, another interference wavefront analyzer which is obtained according to this second possibility, an 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 for optimal use of the photosensitive surface of a wavefront 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 diffracting pattern repetition pitch and the prescribed value of the X wavelength are related by the following nominal equation: pn = 2√Xf / (3√2-pn), where pn denotes the repetition pitch of the diffracting pattern along the symmetry axes of the diffraction grating in the superposition plane, and pn denotes the microlens pitch along the symmetry axes of the microlens array. For the 3-f / 2 configuration, the nominal equation is: p[2] = 2√3√2-Xf / pn.However, one advantage of a wavefront analyzer that is constructed 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 X as resulting from the nominal relationships.

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

[0022] When such a prescribed value X is provided with the optical component, its diffracting pattern can advantageously be adapted to produce, on a spectral component of the radiation beam to be analyzed that has the prescribed value X as its wavelength value, a phase shift that is substantially equal to + / -π(φ) radians, between two complementary zones within the diffracting pattern and for a beam propagation direction that is perpendicular to the superposition plane. This phase shift can 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 within the diffracting pattern. Advantageously, when the pitch of the diffraction grating, denoted p[2, is equal to 2πXf / (31 / 2-pn) and the component If the optical component is intended for use in a wavefront analyzer with an f / 2 configuration, or if the diffraction grating pitch pn is equal to 2-31 / 2-Xf / pn and the optical component is intended for use in a wavefront analyzer with a 3-f / 2 configuration, one of the two complementary areas within the diffracting pattern can be a disk with a diameter approximately equal to 7.66-pi2-31 / 2 / (6-ir). Such a diffraction pattern reduces additional overlaps that might occur in each interferogram with subbeams from microlenses of rank i+3 when that interferogram corresponds to the superposition of subbeams from microlenses of rank i and i+1, i being an integer index of the microlenses that lie successively along one of the axes of symmetry of the microlens array.The analysis of the interferogram to obtain the piston gap value and / or the tilt gap values ​​is then facilitated and more precise.

[0023] A second aspect of the invention proposes an interference wavefront analyzer, which comprises: - - an optical component which conforms to the first aspect above; - an image sensor, which has a flat photosensitive surface and is arranged so 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 towards the image sensor during use of the wavefront analyzer, are captured by the image sensor; and - optionally to provide automated interferogram analysis operation, a processing module, adapted to determine piston gap values, and possibly also tilt gap 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 wavefront analyzer can be simple and compact. In particular, its optical part can 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 can be supplied separately and combined according to instructions provided with the optical component to form the wavefront analyzer.

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

[0026] Advantageously, the prescribed wavelength value X is provided with the optical component, and the repetition pitch of the diffracting pattern belongs to one of the aforementioned respective intervals for the f / 2 and 3-f / 2 configurations of the wavefront analyzer. Therefore, when this repetition pitch of the diffracting pattern is within the interval corresponding to the f / 2 configuration, the 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 within the interval corresponding 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 value X of wavelength is between 0.36 pm and 20 pm, that is to say it belongs to the visible or infrared domain excluding the Terahertz domain, the microlens array and the photosensitive surface of the image sensor can be separated by a distance which is less than 5 cm (centimeter), preferably between 1 mm and 30 mm.

[0028] Advantageously to allow easy use of the wavefront analyzer, it may further include 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 proposes a method for analyzing a wavefront of an electromagnetic radiation beam, which comprises the following steps: - provide an optical component that conforms to the first aspect of the invention; - direct the radiation beam through the optical component; - to position an image sensor downstream of the optical component with respect to a direction of propagation of the radiation beam, so that a photosensitive surface of the image sensor cuts superposition volumes of subbeams that are produced by the optical component from the radiation beam; - activate the image sensor to capture interferograms; and - from the captured interferograms, determine piston gap values, and optionally also tilt gap values, which exist at the level of the superposition plane in the wave surface of the radiation beam.

[0030] When the prescribed wavelength value X is provided with the optical component and when the repetition pitch of the diffracting pattern belongs to one of the aforementioned respective intervals for the f / 2 configuration and for the 3-f / 2 configuration of the wavefront analyzer, the method may include an initial step in which one of a set of sources of the radiation beam to be analyzed and the The optical component is selected relative to the other so that a wavelength value of the source assembly is close to the prescribed X value of the optical component, in order to produce 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 X value of the optical component. The image sensor is then arranged downstream of the optical component to form a wavefront analyzer having an f / 2 or 3-f / 2 configuration. For example, an optical component with a prescribed X value of 633 nm can be used for radiation to be analyzed with a wavelength of 612 nm, and an optical component with a prescribed X value of 1 pm can be used for radiation to be analyzed with a wavelength of 1.5 pm.Optimally, the source assembly is such that the radiation it produces has a non-zero intensity spectral component for the wavelength X value prescribed for the optical component.

[0031] In initial possible applications of the method of the invention, portions of the radiation beam passing through different microlenses are produced by separate respective sources, in particular by split-fiber sources, and more especially by split-fiber laser sources, in continuous or pulsed emission mode. These initial applications may aim to superimpose or juxtapose, in a final beam, elementary radiation beams produced respectively by the separate sources, with the respective phases of the elementary beams coinciding so that the final beam has maximum power.The wavefront analyzer of the invention makes it possible to measure piston and / or tilt deviations that exist between elementary beams that are directed to pass through neighboring microlenses, so that the phase shifts that result from these piston and / or tilt deviations are compensated by an appropriate system.

[0032] In possible secondary 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 reflected by that segment passes through one of the microlenses in a one-to-one correspondence between the mirror segments and the microlenses. For these secondary uses, the method further comprises calculating the height and inclination differences that exist between two neighboring segments of the mirror, based on the determined piston and tilt values. Brief description of the figures

[0033] The features and advantages of the present invention will become more apparent in the following detailed description of non-li- exemplary embodiments. mitatives, with reference to the attached 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 in using a wavefront 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 wavefront analyzer which is in accordance with the invention;

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

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

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

[0042] For clarity, the dimensions of the elements shown in these figures do not correspond to actual dimensions or actual dimension ratios. Furthermore, some of these elements are represented only symbolically, and identical reference numerals shown in different figures designate identical elements or elements with identical functions.

[0043] [Fig. 1] shows a superimposed diffraction grating and part of a microlens array, which together constitute an optical component 1 as proposed by the present invention. The microlenses are all identical, converging, and juxtaposed in a first hexagonal array. The representation of this microlens array is limited to seven microlenses in [Fig. 1] for the sake of clarity. Each microlens is individually designated by reference numeral 11 and has a diameter du and a focal length f. The reference numerals An denote the axes of symmetry of the microlens array 11, which are offset by + / -60° from one axis An to the other. The microlenses 11 are juxtaposed parallel to the axes of symmetry An to form their hexagonal array.The step of juxtaposition of the microlenses 11 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 11 which are close together are contiguous with a single point of contact between them in the plane of the microlens array. crolentilles. However, the diameter of the microlenses may be less than their juxtaposition pitch pu, or each microlens 11 may occupy an entire hexagonal unit cell of their network.

[0044] The diffraction grating is also hexagonal and consists of repetitions of a diffracting pattern parallel to the symmetry axes An of this diffraction grating. The symmetry axes An of the diffraction grating are therefore also shifted by + / -60° from one symmetry axis An to the other. The diffracting pattern has a contour in the shape of a regular hexagon, as shown in dashed lines in the local magnification inset of the figure. This diffracting pattern can be divided into two complementary zones Z1 and Z2, zone Z1 having the shape of a disk 12 of diameter dn, which is centered in the pattern. In the case of a phase-type diffraction grating, the diffracting pattern can be characterized by a first optical thickness inside the disk 12, i.e. in the Z1 zone, and by a second optical thickness, which is different from the first, in the Z2 zone.For example, the diffraction grating can be formed by a plate of transparent material with initially parallel faces, in which flat-bottomed holes have been formed at the locations of the ZL zones. In this way, the diffraction grating has a reduced optical thickness in the ZL zones compared to the Z2 zones. Alternatively, each disk 12 can be raised relative to the Z2 zones that are intermediate between the disks 12, so that the diffraction grating has an increased optical thickness in the ZL zones compared to the Z2 zones. Such a diffraction grating with raised disks 12 can be formed by selective etching, masking the ZL zones. Other embodiments are still possible for the diffraction grating, some of which have been mentioned in the general part of this description. pn denotes the repetition pitch of the diffracting pattern parallel to the symmetry axes Ai2.The phase shift produced by a hole or a feature formed in the transparent material plate that constitutes the diffraction grating is known to be: Aq> = 2 - ir«(nl)-h / X, where h is the depth of the hole or the height of the feature, X is the wavelength of the radiation, and n is the refractive index of the transparent material. This phase shift Aq> is a phase lead in the case of a hole and a phase lag in the case of a feature. In possible implementations, the value of the depth or height h can be selected so that Aq> = ±jt.

[0045] For the embodiment of the invention described herein 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. Furthermore, they are oriented with respect to each other such that each axis of symmetry An of the microlens array 11 is angularly offset by 30° with respect to one of the axes of symmetry An of the diffraction grating. diffraction. Moreover, again for the embodiment described here as an example, the spacing pu of the microlens array 11 is approximately 12 times the repetition spacing p 12 of the diffracting pattern. x and y denote two Cartesian axes perpendicular to each other that lie in the superposition plane PS. In what follows, z denotes a third Cartesian axis that is perpendicular to the two axes x and y.

[0046] For electromagnetic radiation propagating substantially parallel to the z-axis, a wavefront of this radiation existing at the superposition plane PS is designated by S hereafter. The wavefront S can have a local advance along the z-axis that varies between different points on this wavefront. In [Fig. 2], Zi is thus the local advance of a portion SI of the wavefront S, and z2 is the local advance of another portion S2 of the wavefront S. The difference in advance of the wavefront S between its portions SI and S2 is then AP = Zi - z2, and is called the piston gap that exists between these two wavefront portions. Values ​​of the piston gap AP will be determined using the invention, between portions of the wavefront S that are superimposed on neighboring microlenses 11 within the optical component 1.

[0047] In addition to its local advance parallel to the z-axis, which can be variable, the wave surface S can have a local inclination that is also variable. Thus, the portion of the wave surface SI can form an angle tx[ with a projection of the x-axis onto a first cutting plane that is parallel to the x and z axes, and simultaneously form another angle tyi with a projection of the y-axis onto a second cutting plane that is parallel to the y and z axes. Similarly, a tilt of the wave surface part S2 can be characterized by the angles tx2 and ty2, which are defined in the same way as txi and tyi of the wave surface part SL. Then, the tilt difference between the parts SI and S2 of the wave surface S can be characterized by the difference values ​​Atx = txi - tx2 and Aty = tyi - ty2, which are commonly referred to as the tilt and tip difference values, respectively, between the wave surface parts SI and S2.Such tilt and tip deviation values ​​can be determined using the invention between portions of the wavefront S that are superimposed on neighboring microlenses 11 within the optical component 1. For a hexagonally symmetric optical component such as that considered in this description, and when this optical component is used in a wavefront analyzer, a variation in tilt, as well as a variation in tip, affecting a portion of the wavefront superimposed on a single microlens, modifies both a fringe pitch value and a fringe orientation in the interferograms in which the subbeams that have passed through this microlens participate. For this reason, the term "tilt deviation values" refers to both the differences Atx and Aty, without distinction, throughout this description.

[0048] In [Fig.3a], F denotes the electromagnetic radiation beam which is incident on optical component 1, and SF.b, SF0, and SF+i denote three subbeams produced by the diffraction grating of optical component 1 from beam F for each of the microlenses 11. Due to the microlenses 11, all the subbeams SFb, SF0, and SF+i 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 at a distance from it by the focal length f. One subbeam SF0 corresponding to diffraction order 0, three other subbeams SF1 each corresponding to a diffraction order -1, and three additional subbeams SF+i each corresponding to a diffraction order +1 then originate from each microlens 11.If the wavefront S is parallel to the xy plane at this microlens 11, these seven subbeams converge at points in the focal plane PF 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 subbeam SF0 converges at the center of the hexagon, and the six subbeams SF i and SF+i converge at its vertices. Due to the diffraction directions, the x-axis as shown in [Fig. 3a] is perpendicular to one of the symmetry axes Ai2 of the diffraction grating. It is also parallel to one of the symmetry axes An of the microlens array 11.

[0049] For a first configuration of a wavefront analyzer 10 according to the invention, referred to as configuration f / 2, the repetition pitch p[2 of the diffracting pattern along each axis A[2 of the diffraction grating is such that the convergence point of each sub-beam SF i or SF+i that originates from a microlens 11 is substantially superimposed, in the focal plane PF, on the convergence point of the sub-beam SF0 that originates from a neighboring microlens, as shown in [Fig. 3a]. For this, the repetition pitch p 12 of the diffracting pattern along the axes A[2, and the pitch pu of the microlenses 11 along the axes An, satisfy the nominal relation: pn = 2«Xf / (31 / 2-pn). Throughout this description, X denotes a wavelength value which is prescribed for optical component 1, and therefore prescribed for each wavefront analyzer which is constructed from this optical component.This prescribed value X is the wavelength to be adopted for the electromagnetic radiation of the beam F during nominal use of the wavefront analyzer 10. The hatched areas in [Fig. 3a] show the overlapping volumes between a subbeam SF+i and a subbeam SEi originating from two adjacent microlenses 11. A photodetection plane, parallel to the overlapping plane PS and denoted PD, with which the overlapping volumes of the subbeams have a maximum cross-sectional area, is located at a distance f / 2 from the overlapping plane PS, downstream of the latter with respect to the direction of propagation of the radiation beam F. The wavefront 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 plane. The photodetection plane PD is located midway between the superposition plane PS and the focal plane PF. The f / 2 value 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 wavefront analyzer. Within the photodetection plane PD, the subbeams SEi and SF+i originating from two adjacent microlenses 11 are superimposed in an interference area AI, where they produce an interferogram that is captured by the image sensor 2. [Fig. 4a] schematically illustrates this principle of AI interference area formation for a given axis of symmetry An. The resulting AI interference areas are aligned in the photodetection plane PD parallel to the axes of symmetry An due to the 30° angular offset between these axes of symmetry An and the axes of symmetry Ai2.The shape of the peripheral boundary of each interference area AI is slightly altered by the positions of the convergence points in the focal plane PF, depending on the local inclinations of the wavefront S relative to the superposition plane PS. The shape of the peripheral boundary of each interference area AI is also altered when the wavelength of the radiation beam F differs from the prescribed value X as determined by the nominal relationship given above, where the repetition pitch p[2] of the diffracting pattern and the pitch pu of the microlens array are 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 to the peripheral boundaries of the interference areas do not affect the content of the interferograms.

[0050] The image sensor 2 is preferably of a matrix type with a spacing 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. Figure 4b shows an image as captured by the sensor 2 during nominal use of the wavefront analyzer 10 of Figure 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 AI contains a separate interferogram, and an indication of the position of the microlenses 11 is shown by superimposition, in projection parallel to the z-axis.

[0051] The characterization of the shape of the wavefront 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 11 from which the two subbeams SEi 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: ti HI 4 AP At, Atv 1 = k- 1 + cos 2n •u + ^+ ^Ax + ^ry [ [ \ #Pi2 xxx where AP is the piston gap which exists between the parts of the wavefront S that are respectively at the level of one and the other of the two neighboring microlenses, such as this AP gap was introduced above with reference to [Fig. 2]. Atx and Aty are the tilt gaps that exist between these parts of the wavefront 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 axes of symmetry An of the microlens array. k is a sensitivity scaling coefficient of the image sensor 2 that is positive and non-zero. The parameters pn and X are retained as defined above. Thus, the interference state at the center of the interferogram, i.e., for x=y=u=0, provides the value of the piston gap AP.All the piston deviation values ​​AP deduced from the set of interferograms then provide a basic characterization of the shape of the wavefront S: they are the sagittal height values, along the z-axis, of the wavefront S for the sampling mesh formed 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 its constituent fringes and the corresponding fringe spacing. Such an additional analysis of the interferogram fringe structures 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 wavefront S at the centers of the microlenses 11. The deduction of all the deviation values... The piston deflection for basic characterization of the wavefront, and optionally of all tilt deviation values ​​for its further characterization, can be performed automatically 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 from each image captured by the sensor 2, associating each interferogram with its position in the image, i.e., its position relative to the microlens array 11, and then to 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 wavefront analyzer which is also in accordance with the invention. The wavefront analyzer 10 of [Fig. 3b] has a 3-f / 2 configuration. For this reason, the optical component 1 still conforms to the description given with reference to [Fig. 1], but it now satisfies the following new nominal relationship: pn = 2-31 / 2-Xf / pn. All the notations introduced previously and relating to the optical component 1 and to the The radiation to be analyzed, including those related to the shape of the wavefront S, are preserved identically. The hatched areas in [Fig. 3b] correspond to the new superposition volumes of the SF1 and SF+1 subbeams originating from neighboring microlenses 11. However, these superposition volumes are now limited downstream to avoid further superpositions with SF0 subbeams. With the new nominal relationship, the subbeam pairs for which optical component 1 produces superpositions are identical to those in [Fig. 3a], except that these superpositions occur at a distance from the PS superposition plane that is greater than the focal length f.The position of the photodetection plane PD for which the interference areas AI are maximal is then at a 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 wavefront analyzer 10. The optical operation of the wavefront analyzer 10, and the principle of analysis of the interferograms it produces, as described for the f / 2 configuration, are identical for the 3-f / 2 configuration. In particular, the formula for the light intensity distribution within each interferogram is the same for both the f / 2 and 3-f / 2 configurations.

[0053] For the embodiments of the invention just described, it is possible that subbeams produced by the optical component 1, but other than those SF1 and SF+1, may interfere with the latter within the interference areas AI. These other subbeams correspond to higher diffraction orders generated by the diffraction grating, and they are likely to reduce the contrast of the interferograms and hinder their analysis. When the diffracting pattern consists, in the PS superposition plane, of a disk 12 of diameter dn inside which the diffraction grating produces a phase shift of + / -ir for the radiation beam F (see the description above with reference to [Fig.1]), it may be advantageous for the diameter dn to be substantially equal to 7.66-pi2-31 / 2 / (6-ir), especially for the f / 2 configuration when pn = 2«Xf / (31 / 2-pn), or for the 3-f / 2 configuration when pn = 2-31 / 2-Xf / pn.Such a sizing of the diffracting pattern reduces or cancels intensities of some of the higher-order subbeams that 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, for achieving a coherent combination of elementary light beams produced by an array of 1000 fiber laser sources. The 1000 laser sources are capable of interfering with each other and are 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 equipped with an output lens 1011, 1012,..., so that the elementary light beam Fb F2,... emanating from this optical fiber is collimated. The number of separate laser sources that thus produce elementary beams in parallel is unlimited and can be, for example, on the order of several hundred thousand. All the elementary beams FB F2,... produced by the laser sources 1000 are brought to be incident on the optical component 1 of the wavefront 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 11 as there are laser sources 1000, and the transverse distribution of the outputs of the optical fibers 1001, 1002,... forms a hexagonal array, corresponding to the arrangement of the microlenses 11 in the microlens array. In this way, a single optical fiber is directed to one of the microlenses 11, which is dedicated to it. The reference numerals 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 numeral 100. In other words, the image focus of lens 101 is superimposed on the object focus of lens 102. The two lenses 101 and 102 have sufficient transverse extensions to contain all the elementary beams Fi, F2,...The afocal optical system 100 is designed to adapt the pitch of the hexagonal array of optical fiber outputs 1001, 1002,... to the pitch of the microlens array 11. The laser sources 1000, together with the afocal optical system 100, constitute the source assembly mentioned in the general section of this description. The wavefront analyzer 10 can be configured with an aperture of f / 2 or 3-f / 2. This configuration allows for the determination of the piston deviations AP and the tilt deviations present between adjacent optical fibers when all the fiber-optic laser sources 1000 are monochromatic with the same common wavelength, which coincides approximately with the prescribed value X of the wavefront analyzer 10.A particular instance of this first use of a wavefront analyzer 10 that conforms to the invention is where the laser sources 1000 are of the pulsed type, each delivering a very short elementary radiation pulse, for example, on the order of a picosecond or less. Once the piston AP deviations 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 radiation pulse with very high power. The respective propagation directions of the elementary pulses can also be determined, using the tilt deviations that exist at the lenses, in order to. to make them all parallel to each other.

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

[0056] References 101 and 102 in [Fig. 5b] further designate two converging lenses. They are located inside an analysis channel denoted ANA, which leads to the wavefront analyzer 10. A semi-reflective plate 104 allows this analysis channel ANA to be coupled to an output of the telescope, in addition to an application channel denoted APP. Lens 101 is positioned in the image of the telescope's focal plane formed by the semi-reflecting plate 104, and lens 102 is positioned downstream of lens 101 at a distance equal to the focal length of lens 102. In this way, lens 102 ensures that the radiation emerging from the telescope is collimated by the time it reaches the optical component 1 of the wavefront analyzer 10, assuming that any defects in 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 made up of all the juxtaposed mirror segments 2001, 2002, 2003, 2004,... These mirror segments are juxtaposed according to a hexagonal lattice to make up the primary mirror 2000, in order to use an optical component 1 of wavefront analyzer as described above. The focal length of 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. In addition, this optical component 1 is oriented and adjusted transversely 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 wavefront analyzer 10 has the f / 2 configuration, but a wavefront analyzer with a 3-f / 2 configuration can be used alternatively.The purpose of this application of the invention is to determine the relative positional errors of the individual mirror segments 2001, 2002, 2003, 2004... The radiation used for this purpose can originate from a star 2200 located at a very great distance from the telescope, towards which the telescope is pointed. Thus, the star 2200, the telescope, the semi-reflecting plate 104, and the lenses 101 and 102 constitute the source assembly as defined in the general part of this description. Each interferogram then allows the determination of the piston gap AP between the light beams reflected by two adjacent mirror segments. This piston gap is equal to twice the height difference between these two segments. mirror segments. Each interferogram also allows the calculation of the inclination difference between the two mirror segments. The heights of mirror segments 2001, 2002, 2003, 2004... and possibly also their inclinations, can then be adjusted according to the measurement values ​​provided by the processing module 3 for the AP piston deviations, and possibly also for the Atx and Aty tilt deviations, in order to reduce or eliminate the height and inclination differences present between neighboring mirror segments.

[0057] It is understood that the invention can be reproduced by modifying secondary aspects of the embodiments described in detail above, while retaining at least some of the advantages mentioned. In particular, the following modifications can 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 can be of an amplitude variation type instead of a phase variation type, in particular with more than two discrete values ​​of amplitude transmission which are different, thus being able to approach a spatially varying amplitude transmission diffraction grating which is sinusoidal; - microlenses may not be contiguous with each other in the superposition plane, particularly when their individual diameter is less than their juxtaposition pitch along the axes of symmetry of their array; - The values ​​of the optical component parameters, and the distance between the image sensor and the superposition plane in the wavefront analyzer, may differ from the nominal values ​​and relationships 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 X value prescribed for the optical component used, as long as the diffraction grating pitch is within the range corresponding 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 wavefront analyzers; and - a wavefront 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 making adaptive or active optics.

Claims

Demands

1. Optical component (1) comprising: - a diffraction grating, hexagonal and having a repetition pitch (pn) of a diffracting pattern along three axes of symmetry (Ai2) of the diffraction grating, characterized in that it further comprises: - a microlens array, also hexagonal, consisting of identical converging microlenses (11), and having a microlens pitch (pu) along three axes of symmetry (An) of the microlens array, the optical component (1) being arranged such 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 such 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, either angularly shifted with respect to 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 microlens pitch (pu) to the repetition pitch of the diffracting pattern (pi2), or to a repetition pitch of an image of the diffracting pattern in the superposition plane (PS), is between 2 and 18, inclusive.

2. 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 that are neighbors in the microlens array are contiguous.

3. Optical component (1) according to claim 1 or 2, wherein 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 onto 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 glued onto 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 microlensing grating (11) is made by means of a spatial light modulator, preferably both the diffraction grating and the microlensing are made together by means of the same spatial light modulator.

5. Optical component (1) according to any one of the preceding claims, further comprising an indication of a prescribed value X of wavelength for a beam (F) of electromagnetic radiation to be analyzed which is intended to pass through the optical component during use of said optical component in an interference wavefront analyzer (10), said optical component producing, during said use, interference between subbeams (SF.b SF+i ) which emerge from the diffraction grating and which have passed through neighboring microlenses (11) in the microlens grating, the repetition pitch of the diffracting pattern (pn), or the repetition pitch of the image of the diffracting pattern in the superposition plane (PS), being between Xf / (2-31 / 2-pn) and 4-Xf / (31 / 2-pn), where f is a focal length of each microlens (11) and pu is the microlens pitch, so that the interferences exist in a plane which is parallel to the superposition plane and at a distance from said superposition plane of f / 2, or the repetition pitch of the diffracting pattern (pi2), or the repetition pitch of the image of the diffracting pattern, in the superposition plane (PS), being between 4-Xf / (31 / 2-pn) and 8-31 / 2-Xf / pn, 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 X as wavelength value, a phase shift which is substantially equal to + / -pi radians, between two complementary zones (Z1, Z2) within the diffracting pattern and for a propagation direction of said radiation beam which is perpendicular to the superposition plane (PS).

7. An interference wavefront analyzer (10), comprising: - an optical component (1) conforming to any one of the preceding claims; and - an image sensor (2), having a flat photosensitive surface and is arranged so 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 during use of the wavefront analyzer (10), are captured by said image sensor.

8. Wavefront analyzer (10) according to claim 7, further comprising: - a processing module (3), adapted to determine piston gap values ​​which exist at the level of the superposition plane (PS) in a wavefront (S) of the beam (F) of radiation 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. Wavefront analyzer (10) according to claim 9, wherein the processing module (3) is further adapted to deduce tilt deviation values ​​existing between the two areas of the wavefront (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. Wavefront analyzer (10) according to any one of claims 7 to 10, wherein the optical component (1) conforms to claim 5 or 6, and a separation distance between the superposition plane (PS) and the photosensitive surface of the image sensor (2) is between f / 8 and 5-f / 8 if the diffracting pattern repetition pitch (pn), or the image repetition pitch of the diffracting pattern in the superposition plane, is between Xf / (2-31 / 2-pn) and 4-Xf / (31 / 2-pn), 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 diffracting pattern repetition pitch (pn), or the image repetition pitch of the diffracting pattern in the superposition plane, is including 4-Xf / (31 / 2-pn) and 8-31 / 2-Xf / pn.

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

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

14. A method according to claim 12 or 13, wherein portions of the radiation beam (F) passing through different microlenses (11) are produced by separate respective 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 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 determine the tilt deviation values ​​that exist at the level of the superposition plane (PS) in the wavefront (S) of the radiation beam (F); and - calculate height and tilt differences that exist between two segments (2001, 2002, 2003,...) close to the mirror (2000), from the values ​​of the piston and tilt differences that have been determined.