Opto-mechanical system and method for focusing a laser beam along a curvilinear trajectory

Abstract

The present invention relates to an opto-mechanical system (100) for focusing a laser beam along a curvilinear trajectory (50). According to the invention, the opto-mechanical focusing system comprises a first optical device and a transmission focusing optical system fixed rigidly to an opto-mechanical mount (8) mounted to rotate about an axis of rotation (18), the first optical device (11) being arranged to receive an incident laser beam (1) propagating along a longitudinal axis (2) aligned and centered on the axis of rotation (18) and to form a laser beam deflected (3) radially by a distance d with respect to the axis of rotation (18) and centered on the optical axis (15) of the focusing optical system (14), the focusing optical system (14) being arranged to form a focused laser beam (5) and a second transmission optical device (12) arranged in a convergent part of the focused laser beam (5).Figure for the abridged version: Fig. 6.

Description

Title of the invention: Opto-mechanical system and method for focusing a laser beam along a curvilinear trajectory Technical field of the invention

[0001] The present invention relates to the technical field of apparatus and methods for focusing a light beam, in particular a laser beam, onto a focal spot of the smallest possible size, i.e. limited by diffraction, and for moving this focal spot along a curvilinear trajectory.

[0002] It relates in particular to an opto-mechanical system and a method for focusing a laser beam along a curvilinear trajectory while limiting geometric optical aberrations at the focal point (or spot). It also relates to an opto-mechanical system and a method for focusing a laser beam that allows the focal spot of the laser beam to be scanned over an image field of view several millimeters in diameter while remaining compact around the focal plane.

[0003] The invention finds particular applications in ocular surgery devices, used especially for operations on the human eye in which a cylinder must be cut, for example for cataract surgery or for a corneal transplant. The invention also finds applications in machine tools for laser cutting or machining of parts, in particular glass parts intended, for example, for electronic device screens. State of the art

[0004] In the above-mentioned field, US patent document 7,618,415 describes, for example, a system comprising a galvanometric mirror scanner for scanning a laser beam focused on a target. The scanner changes the angle of incidence of the laser beam on a focusing lens, which produces a displacement of the focal spot in the image plane. This variation in the angle of incidence on the focusing system produces geometric optical aberrations in the scanned field of view with an aperture greater than a few 2 mm or 10 mm, for example, 5 mm. A complex optical system comprising several lenses can be used to reduce the geometric optical aberrations. However, the resulting focal spot is never diffraction-limited. Such a system is bulky and heavy.Furthermore, all focusing lenses with an image field of view larger than a few millimeters have working distances shorter than their focal length. Finally, a mirror-based scanner sweeps the beam along axes transverse to the longitudinal axis of laser beam propagation. To approximate a trajectory... For a circular trajectory, it is necessary to decompose it into linear segments in both directions. The resulting trajectory is therefore not perfectly circular but contains angles.

[0005] Other patent documents, notably US4,896,944 (Irwin) or US4,969,722 (Akeel), describe a system based on the rotation of a lens or a portion of a lens around an axis of rotation located at an adjustable distance from the optical axis of the focusing lens. Such a system makes it possible to focus a laser beam along a circular path of adjustable diameter, for example, between approximately 0.12 mm and 12 mm. However, these systems exhibit geometric optical aberrations in the scanned image field. Furthermore, the working distance between the focusing lens and the target to be treated is less than the focal length of that lens.

[0006] US patent document 398,676,7 (Rexer) describes an apparatus based on the rotation of an off-axis parabolic mirror and a plane mirror to focus a laser beam along a circular path. To effectively limit geometric optical aberrations, such a system requires very precise alignment of the parabolic mirror's axis. Furthermore, this system exhibits a very small working distance between the plane mirror and the image plane.

[0007] US patent document 9,259,354 (Horvath) describes an ocular surgery system for delivering a laser beam, intended in particular for cataract surgery. This system is also based on the rotation of a lens around an axis of rotation located at a distance from the optical axis of the focusing lens to focus a laser beam along a circular path of adjustable diameter. Horvath acknowledges that the use of a lens whose optical axis is decentered with respect to that of the incident beam introduces optical aberrations that reduce the quality of the beam and increase the size of the spot obtained inside the eye. In one embodiment, the laser beam incident on the lens has an aperture much larger than the aperture of the lens, which reduces the optical power delivered and induces inhomogeneities during the rotation of the lens.In another embodiment, the laser beam incident on the lens has an aperture smaller than the lens, which increases the spot size. Horvath describes the use of a lens with a complex shape and asymmetrical shape with respect to its optical axis to correct certain optical aberrations. These lenses are particularly difficult to manufacture. Moreover, the working distance between the last surface of the focusing system and the image plane is quite small.

[0008] One of the aims of the invention is to provide a system and a method for focusing a laser beam into a spot corrected as much as possible for optical aberrations, with the spot being scanned along a curvilinear trajectory and which has a reduced size around the focal plane, particularly for ophthalmological applications where the patient's nose or eyebrow may interfere with access to the eye.

[0009] Yet another object of the invention is to propose a system and a method of focusing a laser beam enabling the maximum power of the incident laser beam to be delivered and providing a spot of uniform intensity over the entire curvilinear trajectory in the focal plane.

[0010] In addition, it is desirable that the opto-mechanical system and the laser beam focusing method be adapted to adjust the focal plane of the spot to allow a helical trajectory of the spot. Presentation of the invention

[0011] In this context, the present invention proposes an opto-mechanical system for focusing a laser beam along a curvilinear trajectory.

[0012] More particularly, according to the invention, an opto-mechanical focusing system is proposed comprising: an opto-mechanical mount movable in rotation about an axis of rotation, a transmission focusing optical system and a first optical device disposed upstream of the focusing optical system, the first optical device and the transmission focusing optical system being fixed securely to the rotating movable opto-mechanical mount, the focusing optical system having an optical axis radially offset by a non-zero distance equal to d with respect to the axis of rotation;the first optical device being arranged to receive an incident laser beam propagating along a longitudinal axis aligned and centered on the axis of rotation, the first optical device being arranged and configured to form a deflected laser beam propagating along a longitudinal axis radially offset by the distance d with respect to the axis of rotation and centered on the optical axis of the focusing optical system;the focusing optical system being arranged to receive the laser beam deflected by the first optical device and to form a laser beam focused on its optical axis, and a second transmitting optical device disposed downstream of the focusing optical system in a convergent part of the focused laser beam, the second optical device having an entrance face perpendicular to the axis of rotation and an optical thickness adapted to extend a working distance of the focusing optical system by a distance dz along the optical axis. ;

[0013] Thus, the opto-mechanical focusing system makes it possible to move the focused laser beam spot along a curvilinear trajectory, while avoiding the introduction of geometric optical aberrations, except possibly for spherical aberration. The laser beam spot has a constant size and is close to the diffraction limits along the entire curvilinear trajectory. Furthermore, this opto-mechanical focusing system This system allows for an increased working distance between the optical focusing system and the patient's eye or the object to be cut / machined, greatly facilitating the procedure. Furthermore, this opto-mechanical focusing system operates without vignetting of the incident laser beam, thus eliminating optical power loss. Finally, this opto-mechanical system ensures a curvilinear trajectory of the focused spot without relative movement between the deflected laser beam and the focusing system.

[0014] Other non-limiting and advantageous features of the system according to the invention, taken individually or according to all technically possible combinations, are as follows.

[0015] In one embodiment, the first optical device comprises a flat, parallel-sided blade, a normal to an entrance face of the blade being inclined at an angle between 5 and 60 degrees with respect to the axis of rotation.

[0016] According to a particular and advantageous aspect, the opto-mechanical focusing system includes means for adjusting the angle of inclination of said blade with flat and parallel faces.

[0017] According to another particular aspect, the focusing optical system comprises a plano-convex lens or a biconvex lens.

[0018] Advantageously, the optical focusing system comprises a symmetrical aspheric lens of revolution about the optical axis.

[0019] Preferably, said aspheric lens has an exit face having a spherical radius of curvature adapted to compensate for a spherical aberration introduced by the second optical device.

[0020] In one embodiment, the second optical device comprises a flat, parallel-sided blade arranged perpendicular to the axis of rotation, said blade having an optical refractive index greater than or equal to 1.3 and a physical thickness between 1 mm and 50 mm.

[0021] According to a particular and advantageous aspect, the opto-mechanical focusing system includes means for translating the opto-mechanical mount, the translation means having an axis of translation parallel to the axis of rotation.

[0022] This disclosure also relates to an ophthalmic surgery device comprising a laser connected by optical fiber to a hand tool for applying a laser beam to the eye of a patient with a vision defect, wherein the hand tool includes an opto-mechanical focusing system according to one of the embodiments described.

[0023] This disclosure also relates to a laser cutting or machining device comprising an opto-mechanical focusing system according to one of the embodiments described.

[0024] The invention also relates to a method for focusing a laser beam along a curvilinear trajectory for cutting or machining mechanical, electronic or biological parts, the method comprising the following steps: - direct an incident laser beam, propagating along a longitudinal axis aligned and centered on an axis of rotation, towards a first optical device arranged and configured to form a deflected laser beam propagating along a longitudinal axis radially offset by a non-zero distance d with respect to the axis of rotation; - receive the deflected laser beam on a transmission focusing optical system having an optical axis radially offset by a non-zero distance equal to the distance d with respect to the axis of rotation, the deflected laser beam being centered on the optical axis of the focusing optical system, to form a laser beam focused on its optical axis; - transmit the focused laser beam through a second optical transmission device disposed downstream of the focusing optical system in a convergent part of the laser beam, the second optical device having an optical thickness adapted to extend the working distance of the focusing optical system by a distance dz, and - apply a rotation jointly to the first optical device and the focusing optical system around the axis of rotation to sweep the focused laser beam along a curvilinear trajectory.

[0025] Of course, the various features, variants, and embodiments of the invention can be combined with one another in various ways, provided they are not incompatible or mutually exclusive. Brief description of the drawings

[0026] In addition, various other features of the invention become apparent from the attached description made with reference to the drawings which illustrate non-limiting embodiments of the invention and where:

[0027] [Fig-1] is a longitudinal cross-sectional view of an opto-mechanical system according to a embodiment, in a first position allowing a laser beam to be focused at a first point on a curvilinear trajectory;

[0028] [Fig.2] is a longitudinal cross-sectional view of the same opto-mechanical system as the [Fig.l], in a second position allowing the laser beam to be focused at a second point on the curvilinear trajectory;

[0029] [Fig.3] is a longitudinal cross-sectional view of the same opto-mechanical system as on figures 1-2, in a third position allowing the laser beam to be focused at a third point on the curvilinear trajectory;

[0030] [Fig.4] is a longitudinal sectional view of a first optical device forming part of an opto-mechanical system according to a particular embodiment of the present disclosure;

[0031] [Fig.5] is a longitudinal sectional view of an opto-mechanical mount including a first optical device and a focusing lens and illustrating the opto-mechanical operation of these elements;

[0032] [Fig.6] is a longitudinal cross-sectional view of an opto-mechanical system according to a particular embodiment of the present disclosure.

[0033] It should be noted that in these figures the structural and / or functional elements common to the different variants may have the same references. Detailed description

[0034] In the following description, a system and a method for focusing a laser beam are described. However, this disclosure applies more generally to the focusing of a collimated incident light beam. A collimated beam is understood to be a light beam of finite dimensions having a small but non-zero divergence. The divergence angle of a beam is denoted by θ, that is, the angle between the longitudinal direction of propagation of this beam and the tangent to the intensity profile at full height. In the case of a laser beam, the divergence is defined as the angle between the longitudinal direction of propagation and the line connecting the points of intensity equal to 13.5% of the peak intensity of the beam propagating in the longitudinal direction of propagation.

[0035] Figure 1 schematically shows an opto-mechanical focusing system 100 for a laser beam according to one embodiment. The opto-mechanical focusing system comprises an opto-mechanical mount 8 mounted to rotate about an axis of rotation 18. As is known, the opto-mechanical mount 8 comprises, for example, a fixed part and a movable part. A drive system, preferably motorized, allows the movable part of the opto-mechanical mount 8 to rotate relative to its fixed part about the axis of rotation 18. The speed or rotational frequency of the opto-mechanical mount 8 is between 1 and 200 revolutions per second.

[0036] The opto-mechanical focusing system 100 mainly comprises the following optical elements arranged optically in series: a first optical device 11, a focusing optical system 14, and a second optical device 12. The first optical device 11 and the focusing optical system 14 are fixed rigidly to the rotatable opto-mechanical mount 8. The second optical device 12 is independent of the opto-mechanical mount 8. Alternatively, the second optical device 12 is securely connected to the fixed part of the opto-mechanical frame 8.

[0037] We will now describe the operation of the opto-mechanical system 100 for focusing a laser beam to a point with little or no optical aberrations and for scanning the focused laser beam along a curvilinear trajectory.

[0038] The first optical device 11, the focusing optical system 14 and the second optical device 12 preferably operate in transmission. For example, the first optical device 11 comprises a plate with flat and parallel faces inclined with respect to the incident beam, as illustrated in Figures 4 to 6. Alternatively, the first device 11 comprises two parallel mirrors, or two prisms whose facing surfaces are parallel, or a direct vision prism (known as an Amici prism), or any other optical system that laterally shifts the beam parallel to its longitudinal direction of propagation.

[0039] The focusing optical system 14 has an optical axis 15. The focusing optical system 14 is mounted in the opto-mechanical mount so that the optical axis 15 is parallel to the rotation axis 18 of the mount and radially offset by a non-zero distance equal to d with respect to the rotation axis 18.

[0040] In the embodiment illustrated in Figures 1-3, the focusing optical system 14 comprises a single lens. Alternatively, the focusing optical system 14 comprises several lenses, possibly joined together.

[0041] An incident laser beam 1 propagating along a longitudinal axis 2 is directed towards the opto-mechanical focusing system 100. The opto-mechanical focusing system 100 is arranged and oriented so that the rotation axis 18 and the propagation axis 2 are aligned and centered with respect to each other.

[0042] Preferably, the incident laser beam is collimated. For example, the incident laser beam 1 is a beam that has a divergence of less than 1 milliradian (mrad) about the longitudinal axis 2. The intensity cross-section of the incident laser beam is, for example, Gaussian or spatially shaped, for example, into a top hat or a truncated Gaussian. In one embodiment, the system 100 of this disclosure further includes an optical collimation system disposed upstream of the first optical device, the optical collimation system being arranged and configured to reduce the divergence of the laser beam incident on the first optical device.

[0043] The first optical device links an entrance face 111 adapted to receive the incident laser beam 1 propagating along the longitudinal axis 2 aligned and centered on the axis of rotation 18. The optical aperture of the first optical device is greater than or equal to the aperture of the incident laser beam 1. For example, the first optical device links a circular aperture with a diameter between 10 mm and 25 mm and the beam The incident laser 1 has a circular aperture of diameter D, ranging from 1 mm to 20 mm. Here, the aperture of the incident laser beam is defined as the full width at half maximum (FWHM) on the entrance face 111 of the first optical device 11. Alternatively, the laser beam aperture is the 1 / e2 intensity width of the laser beam incident on the entrance face 111.

[0044] The first optical device 11 is arranged and oriented in the opto-mechanical mount 8 to laterally deflect the incident laser beam. In particular, the first optical device 11 is arranged to form a deflected laser beam 3 propagating along a longitudinal axis 4 perfectly parallel to the longitudinal axis 2, radially offset by a distance d from the rotation axis 18 and centered on the optical axis 15 of the focusing optical system 14. More precisely, the radial offset induced by the first optical device 11 is exactly equal in magnitude and direction (i.e., vectorially) to the radial offset d between the rotation axis 18 and the optical axis 15 of the focusing system. The first optical device connects to an output face 112 which transmits the deflected laser beam 3.

[0045] Furthermore, the first optical device 11 does not alter the divergence of the laser beam. In other words, the aperture of the deflected laser beam 3 is identical to the aperture of the incident laser beam 1.

[0046] The deflected laser beam 3 propagates in free space, for example in air, between the output face 112 of the first optical device 11 and the focusing optical system 14.

[0047] The laser beam, deflected radially by a distance d, is incident on the entrance face 141 of the focusing optical system 14. As indicated above, the deflected laser beam 3 is exactly centered on the optical axis 15 of the focusing optical system 14. The focusing optical system 14 is arranged to receive the deflected laser beam 3 by the first optical device 11 and to form a focused laser beam 5 that converges towards the optical axis 15. Advantageously, the optical aperture of the focusing optical system 14 is larger than the aperture of the deflected laser beam 3. In this way, the focusing optical system 14 does not reduce the intensity of the transmitted laser beam.

[0048] In the example illustrated in Figures 1-3, the focusing optical system 14 is a lens system comprising a single lens, for example, a plano-convex or biconvex lens. For example, the entrance face 141 of the focusing optical system 14 is convex. The focusing optical system 14 has a focal length denoted F. The focusing optical system 14, used without the second optical device, has a working distance less than or equal to its focal length. The working distance is the free space between the exit face 142 of the focusing optical system 14 and the focal point. For example, the focusing optical system 14 has a The focal length (F) is between 20 mm and 100 mm, for example 40 mm, the optical aperture is between 5 mm and 40 mm, and the working distance is between 10 mm and 90 mm. In particular, the focusing optical system has a focal length of 40 mm, a working distance of 34.5 mm, and a diameter of 25 mm.

[0049] The second optical device 12 is disposed downstream of the focusing optical system 14 in a convergent portion of the focused laser beam 5, that is, between the output face 142 of the focusing optical system 14 and the focal plane. The second optical device 12 has a flat input face 121 disposed perpendicular to the axis of rotation 18 of the opto-mechanical mount 8. The second optical device 12 has an optical thickness adapted to extend the working distance of the focusing optical system 14 by a distance dz along the optical axis 15.

[0050] In one embodiment, the second optical device 12 consists of a plate with flat, parallel faces, of thickness denoted e and of refractive index denoted n. The entrance face 121 of the second optical device 12 is arranged perpendicular to the axis of rotation 18 of the opto-mechanical mount. Consequently, the entrance face 121 of the second optical device 12 is arranged perpendicular to the optical axis 15 of the focusing optical system 14. The second optical device 12 has the effect of increasing the working distance by a value equal to dz = e (1-1 / n).

[0051] The second optical device 12 receives the converging portion of the focused beam 5 and transmits a focused beam 7 propagating along the optical axis 15, the focal point of which is offset from the focusing system by a distance dz along the optical axis 15. The second optical device 12 has an optical aperture larger than the aperture of the focused laser beam 5. However, the second optical device 12 advantageously has a conical or partially conical shape with an output face 122 whose optical aperture is smaller than that of the optical aperture of the input face 121 or the aperture of the focusing optical system, and a reduced size compared to the size of the opto-mechanical frame. This reduced size avoids interference from the nose or eyebrow during eye surgery.

[0052] Consequently, in a static position, the opto-mechanical focusing system 100 receives the incident laser beam 1 centered on the rotation axis 18 and forms a laser beam focused at a point radially offset by a distance d from the rotation axis 18 and at a distance equal to the sum F + dz from the output face of the focusing optical system 14, where F represents the focal length of the system focusing optics 14 and dz the increase in working distance induced by the second optical device 12.

[0053] However, the second optical device 12, consisting of a parallel-sided plane plate, introduces geometric optical aberrations due to the aperture and convergence of the focused laser beam 5. Positioning this parallel-sided plane plate perpendicular to the optical axis 4 of the focused laser beam 5 eliminates higher-order optical aberrations such as coma, astigmatism, distortion, and field curvature. Nevertheless, this plate introduces spherical aberration. In the case of a parallel-sided plane plate, this spherical aberration is measured by the impulse response dy' measured in the plane of the paraxial image using the following equation: '1 dy* = — é—

[0054] where e is the thickness of the plate, n its refractive index, and θ the angle between a ray of the beam and the normal to the face of the plate. A collimated beam parallel to the normal (θ = 0) does not undergo any spherical aberration. In the present case, since the laser beam 5 is convergent (θ₀) and its principal ray is perpendicular to the face of the plate 12 (α = 0), it only undergoes spherical aberration of the opposite sign to that of a plane-spherical converging lens. Conversely, a convergent or divergent beam (θ₀) whose principal ray is not perpendicular to the face of the plate 12 (α = 0) undergoes all third-order aberrations (i.e., coma, astigmatism, distortion, and field curvature).

[0055] Advantageously, a focusing optical system is used comprising a suitable aspherical lens to correct the spherical aberration induced by the subset formed by the focusing optical system and the second optical device 12, taking into account the aperture of the laser beam. This single correction of spherical aberration makes it possible to obtain, at the focal point 51, 52, 53, a diffraction-limited focal spot even for a large numerical aperture, on the order of 0.1 to 0.4. Indeed, by construction as detailed above, all other geometric optical aberrations are zero.

[0056] For example, we start with a focusing optical system comprising a lens having a first face or entrance face 141 and a second face or exit face 142. This lens can be made stigmatic for a collimated incident beam perpendicular to the entrance face 141 by giving this entrance face 141 an aspheric shape calculated to compensate for the spherical aberrations of this lens in air. When an optical device 12 is introduced after the aspheric focusing system, the optical device 12 introduces a complementary spherical aberration that is not compensated. An inexpensive solution for correcting the aberration The spherical method involves using the exit face 142 of the focusing lens 14, slightly increasing its power by introducing a spherical profile for this face or increasing its curvature. Since the spherical aberration of a converging diopter is opposite in sign to that of a plate with parallel, flat faces, a curvature can be found that compensates for the spherical aberrations introduced by the second plate 12. The fabrication of such a biconvex lens can be achieved quite easily by bonding a second lens to the exit face of the initial lens. One face of this second lens has a curvature identical to that of the exit face of the first lens, while the other face is spherical with a curvature calculated to compensate for the aberrations of the plate of the second optical device 12.

[0057] In [Fig. 1], the opto-mechanical mount 8 is shown in a first position. An orthonormal coordinate system XYZ is also schematically represented, in which the Z-axis is parallel to the rotation axis 18 and to the optical axis 2 of the incident laser beam 1. In this first position, the first optical device 11 laterally deflects the incident laser beam by a radial distance d in the direction of the X-axis or +X direction. The focusing optical system 14 and the second optical device 12 focus the laser beam to a first focal point 51, which is radially offset from the rotation axis 18 by a distance d in the +X direction and located in a focal plane at a distance equal to F+dz from the output face 142 of the focusing optical system 14 in the direction of the Z-axis, where F represents the focal length of the focusing optical system 14 and dz the extension of the working distance induced by the second optical device 12.Advantageously, the working distance between the output face of the second optical device 12 and the first focusing point 51 is greater than the working distance of the focusing optical system 14. This increased working distance reduces the overall size of the system around the focusing point. As mentioned above, the second optical device 12 is located in the converging portion of the focused laser beam. The second optical device 12 can have an aperture smaller than the aperture D of the focusing optical system without obstructing the beam, and therefore without any loss of optical power.

[0058] In [Fig.2], the opto-mechanical mount 8 is shown in a second position, relative to the same orthonormal coordinate system XYZ as in [Fig. 1]. In this second position, the first optical device 11 laterally deflects the incident laser beam by a radial distance d in the direction opposite to the X-axis, or -X direction. The focusing optical system 14 and the second optical device 12 focus the laser beam to a second focal point 52, which is radially offset from the rotation axis 18 by a distance d in the +X direction and located in the focusing plane at distance F+dz from the output face 142 of the focusing optical system 14.

[0059] In [Fig. 3], the opto-mechanical mount 8 is shown in a third position, relative to the same orthonormal coordinate system XYZ as in Figures 1 and 2. In this third position, the first optical device 11 laterally deflects the incident laser beam by a radial distance d in the direction opposite to the Y axis or direction -Y. The focusing optical system 14 and the second optical device 12 focus the laser beam to a third focal point 53, which is radially offset with respect to the rotation axis 18 by a distance d in the direction -Y and located in the focal plane at a distance F+dz from the output face 142 of the focusing optical system 14.

[0060] It follows that rotating the opto-mechanical mount 8 around its axis of rotation 18 allows the laser beam focused at a point to be scanned along a circular path 50 with a radius equal to the distance d around this axis of rotation. As can be seen in Figures 1-3, the principal ray of the deflected laser beam incident on the focusing system 14 remains perfectly centered on the optical axis of the focusing optical system 14 during the rotation of the opto-mechanical mount 8, regardless of the position of the focal point 51, 52, 53 on the curvilinear path. Furthermore, the principal ray on the optical axis of the laser beam incident on the second optical device 12 also remains perpendicular to the entrance face 121 of the second optical device 12 during the rotation of the opto-mechanical mount and the circular path of the focal point.

[0061] The scanning of the focused laser beam in the image plane sweeps an image field of view with a diameter equal to 2*d. Nevertheless, the optical aberrations at the focal point are much lower than in prior art systems.

[0062] This particular configuration of the system of the present disclosure allows the main ray of the laser beam to avoid third-order geometric optical aberration when passing through the focusing optical system 14 and the second optical device 12. In this configuration, the subset formed by the focusing optical system 14 and the second optical device 12 induces only spherical aberration, which remains constant along the entire curvilinear path of diameter 2*d. Indeed, only the rays corresponding to the largest aperture of the laser beam are inclined at the entrance face of the focusing optical system 14 and the second optical device 12. Moreover, the inclination of these peripheral rays remains identical in absolute value during the rotation of the opto-mechanical mount 8 around its axis of rotation 18.

[0063] As mentioned above, this spherical aberration is advantageously corrected by a specific focusing optical system 14 having an aspherical surface and symmetrical about its optical axis 15. In this way, the correction of spherical aberration at a point on the circular trajectory allows for correction that is effective over the entire circular trajectory of diameter 2*d. As a non-limiting example, an aspheric lens, symmetrical about its optical axis, marketed by Asphericon GmbH (Jena, Germany), is used.

[0064] This gives us an opto-mechanical system which makes it possible to focus a laser beam at a focal point exhibiting very low optical aberrations and thus a focal spot of very small diameter, close to the theoretical limits of the Airy spot.

[0065] During the rotation of the opto-mechanical mount 8, the laser beam is entirely transmitted through the first optical device 11, the focusing optical system 14, and the second optical device 12. The opto-mechanical focusing system 100 for a laser beam does not produce any optical power loss due to vignetting. On the contrary, the incident laser beam 1 can have the same aperture as the focusing optical system 14, which makes it possible to reduce the size of the focal spot. A focal spot is obtained that is practically limited by diffraction, i.e., by the diameter D of the incident laser beam 1. For example, for a beam size D of approximately 15 mm, a spot size of approximately 4.5 µm is obtained. Furthermore, the luminous intensity of the focused beam remains constant during the beam scanning along the curvilinear path 50.

[0066] Figure 4 shows an example of a first optical device 11, here consisting of a blade whose faces 111 and 112 are flat and parallel. The normal to the entrance face 111 is inclined at an angle denoted α with respect to the axis of rotation 18, which coincides with the optical axis 2 of the incident laser beam 1. A plane of incidence is defined by the optical axis 2 of the incident laser beam 1 and the normal to the entrance face 111. The blade 11 has a thickness ei and a refractive index denoted nb. The blade with flat and parallel faces deflects the incident laser beam 1 radially in the plane of incidence by a distance d equal to: ( 1 — ,sàr(«) J (m)2 —

[0067] Thus, a displacement d of 2.5 mm is obtained with a borosilicate crown glass plate (also called BK7) having a refractive index ni of -1.51 at the wavelength of the laser beam (approximately 1030 nm), a thickness ei of 20.32 mm, and which is inclined at an angle θ of 20 degrees with respect to an incident laser beam, for example at a wavelength of 1030 nm. As described above, this displacement d of 2.5 mm makes it possible to obtain a circular trajectory with a diameter of 5 mm, suitable, for example, for An ocular surgery device that allows for the surgical incision of the lens capsule, or capsulotomy. In another example, the offset d is 4.5 mm. For ophthalmic surgery applications, the offset d is generally between 1 and 5 mm.

[0068] Adjusting the tilt angle of the parallel-sided, flat-faced blade 11 allows the radial offset distance d of the laser beam to be varied in order to adjust the diameter of the circular beam path. However, the tilt angle of the parallel-sided, flat-faced blade 11 is preferably fixed, the blade being rigidly mounted to the opto-mechanical mount 8.

[0069] It is also possible to manufacture several interchangeable opto-mechanical mounts 8, each having a blade 11 of a different thickness, each blade being inclined at the same angle α, for example 20 degrees. Each opto-mechanical mount thus makes it possible to provide a different radial offset depending on the thickness of its blade, the radial offset ranging, for example, from 1 to 5 mm.

[0070] If the incident laser beam 1 is collimated, the first optical device 11 introduces no optical aberration on the deflected laser beam 3. In this case, the deflected laser beam 3 incident on the focusing optical system is collimated and centered on the optical axis 15 of this focusing optical system 14. The deflected laser beam 3 emerging from this blade is by construction exactly parallel to the incident laser beam 1.

[0071] [Fig.5] schematically shows an opto-mechanical mount 8 comprising the blade 11 described in connection with [Fig.4] and a focusing lens 14. The focusing lens 14 is mounted in the mount 8 with an offset of its optical axis 15 equal to the distance d calculated above with respect to the axis of rotation 18 of the mount 8 in the direction of the offset induced by the blade 11.

[0072] The blade 11 and the focusing lens 14 are fixedly mounted on the rotating part of the opto-mechanical mount 8 such that the optical axis of the focusing lens 14 is aligned and centered on the rotation axis 18 of the opto-mechanical mount. In this way, a rotation R of the assembly formed by the opto-mechanical mount 8, the blade 11, and the focusing lens 14 causes the laser beam to describe a circular path 50 in the focal plane. The radius of this circle is the offset d introduced by the blade.

[0073] As indicated above, the focused laser beam 5 exhibits only spherical aberration, the other geometric optical aberrations being all zero.

[0074] Figure 6 schematically shows an opto-mechanical system according to a particular embodiment of the present disclosure. The system comprises an opto-mechanical mount 8 including the blade 11 and a focusing lens 14 described in connection with Figures 4 and 5 and an example of a second optical device 12. The second optical device 12 is here made up of a blade whose faces 121 and 122 are flat and parallel and arranged perpendicular to the optical axis 15 coincident with the axis of rotation 18.

[0075] In one particular embodiment, the second optical device 12 is a flat, parallel-sided blade made of high-index flint glass (for example, type SF57 or SF59 from Schott), i.e., with a relatively high refractive index, denoted n, for example, 1.7, and a thickness e of approximately 5 cm. Such a blade makes it possible to extend the working distance by about 30 mm. The blade has a diameter large enough not to obstruct the laser beam. In the example cited above, the blade 12 has a diameter greater than D and, for example, equal to the aperture of the focusing system 14. A smaller diameter does not change the extension introduced by the blade but risks causing partial obstruction of the beam.

[0076] Alternatively, the second optical device comprises several flat and parallel face plates 126, 127, 128 arranged in series with indices n; equal or different and having a total optical thickness equal to S(ni*ei), the faces of these plates being perpendicular to the optical axis of the focusing optical system and to the axis of rotation of the opto-mechanical mount.

[0077] According to another embodiment, the second optical device comprises a cube made up of two right prisms, each having a high refractive index, for example, of 1.8. Such a polarizing or dichroic cube makes it possible to combine an optical viewing channel with the focusing laser beam. By reflection on the target, for example, the patient's eye, the surgeon can thus verify, via an eyepiece, the correct centering of the circular path of the laser beam with respect to the patient's eye.

[0078] In a particular and advantageous embodiment, the opto-mechanical mount 8 is further mounted to move in translation along an axis parallel to the axis of rotation 18. Another drive system 20, preferably motorized, allows the opto-mechanical mount 8 to be moved longitudinally parallel to the axis of rotation 18. The longitudinal movement also drives the second optical device so as to move the focal plane of the laser spot. The amplitude of the longitudinal movement is between 0 and 5 mm, for example limited to about 2 mm in a capsulotomy application. The translational speed of the opto-mechanical mount 8 is between 0.1 and 10 mm per second. This longitudinal movement allows the position of the focal plane to be adjusted relative to the target.

[0079] In a particular embodiment, a rotational movement R and a translational displacement are simultaneously applied to the opto-mechanical focusing system 100 of a laser beam so as to sweep the focusing spot along a trajectory on the surface of a cylinder of diameter 2*d, in particular for example a helical trajectory.

[0080] Such a laser beam focusing system along a circular or cylindrical trajectory makes it possible to cut various materials. For example, such a system applied to a transparent material makes it possible to cut a perfectly cylindrical core from the thickness of the material. The resulting cylindrical hole is perfectly circular. In contrast, a laser beam scanning system using a galvanometric scanner operates by successive movements along two fixed directions, which can only describe a circle by approximation via a series of straight steps and produces a hole with serrated edges.

[0081] The focusing system of this disclosure finds applications, in particular, in ocular surgery for capsulotomy or corneal transplantation. The focusing system of this disclosure is compact, lightweight, and has a small footprint in the focal plane, while still producing a very small focal spot. The focusing system is easily integrated into a handheld tool connected by optical fiber to a laser, the handheld tool being intended to be operated by a surgeon or operator to apply the laser beam to a patient's eye.

[0082] The focusing system of the present disclosure finds other applications in the cutting of glass plates used for example in screens.

Claims

Demands

1. Opto-mechanical system (100) for focusing a laser beam along a curvilinear trajectory (50), characterized in that the opto-mechanical focusing system comprises: - an opto-mechanical mount (8) mounted movable in rotation about an axis of rotation (18), an optical focusing system (14) in transmission and a first optical device (11) disposed upstream of the optical focusing system, the first optical device and the optical focusing system in transmission being fixed rigidly to the movable in rotation opto-mechanical mount, the optical focusing system having an optical axis (15) radially offset by a non-zero distance equal to d with respect to the axis of rotation (18);- the first optical device (11) being arranged to receive an incident laser beam (1) propagating along a longitudinal axis (2) aligned and centered on the axis of rotation (18), the first optical device (11) being arranged and configured to form a deflected laser beam (3) propagating along a longitudinal axis (4) radially offset by the distance d with respect to the axis of rotation (18) and centered on the optical axis (15) of the focusing optical system (14);- the focusing optical system (14) being arranged to receive the laser beam deflected (3) by the first optical device and to form a focused laser beam (5) on its optical axis (15), and - a second transmitting optical device (12) arranged downstream of the focusing optical system (14) in a convergent part of the focused laser beam (5), the second optical device (12) having an entrance face (121) perpendicular to the axis of rotation and an optical thickness adapted to extend a working distance of the focusing optical system (14) by a distance dz along the optical axis (15).;

2. Opto-mechanical focusing system (100) according to claim 1 in which the first optical device comprises a blade with flat and parallel faces, a normal to an entrance face of the blade being inclined at an angle between 5 and 60 degrees with respect to the axis of rotation (18).

3. Opto-mechanical focusing system (100) according to claim 2 comprising means for adjusting the angle of inclination of said blade with flat and parallel faces.

4. Opto-mechanical focusing system (100) according to any one of claims 1 to 3 wherein the optical focusing system comprises a plano-convex lens or a biconvex lens.

5. Opto-mechanical focusing system (100) according to any one of claims 1 to 4 in which the optical focusing system comprises a symmetrical aspheric lens of revolution about the optical axis (15).

6. Opto-mechanical focusing system (100) according to claim 5 in which said aspheric lens has an exit face having a spherical radius of curvature adapted to compensate for a spherical aberration introduced by the second optical device (12).

7. Opto-mechanical focusing system (100) according to any one of claims 1 to 6 in which the second optical device comprises a blade with flat and parallel faces arranged perpendicular to the axis of rotation, said blade having an optical refractive index greater than or equal to 1.3 and a physical thickness between 1 mm and 50 mm.

8. Opto-mechanical focusing system (100) according to any one of claims 1 to 7 comprising means for translating the opto-mechanical mount, the translation means having an axis of translation parallel to the axis of rotation (18).

9. Ophthalmic surgery apparatus comprising a laser connected by optical fiber to a hand tool for applying a laser beam to the eye of a patient with a vision defect, wherein the hand tool includes an opto-mechanical focusing system according to any one of claims 1 to 8.

10. Laser cutting or machining apparatus comprising an opto-mechanical focusing system according to any one of claims 1 to 8.

11. Method of focusing a laser beam along a curvilinear path for cutting or machining mechanical, electronic or biological parts, comprising the following steps: - directing an incident laser beam (1), propagating along a longitudinal axis (2) aligned and centered on an axis of rotation (18), towards a first optical device (11) arranged and configured to form a deflected laser beam (3) propagating along a longitudinal axis (4) radially offset by a non-zero distance d with respect to the axis of rotation (18); - receive the deflected laser beam (3) on a transmission focusing optical system (14) having an optical axis (15) radially offset by a non-zero distance equal to the distance d with respect to the axis of rotation (18), the deflected laser beam (3) being centered on the optical axis (15) of the focusing optical system, to form a focused laser beam (5) on its optical axis (15); - transmit the focused laser beam (5) through a second optical transmission device (12) disposed downstream of the focusing optical system in a convergent part of the laser beam, the second optical device having an optical thickness adapted to lengthen the working distance of the focusing optical system (14) by a distance dz, and - apply a rotation jointly to the first optical device (11) and to the focusing optical system (14) around the axis of rotation (18) to sweep the focused laser beam along a curvilinear trajectory (50).