Laser system with monolithic optical collimating and circularizing device

Abstract

The present invention relates to a laser system (1) including a solid-state amplifying medium (2) capable of emitting an amplified beam (4) in a propagation direction (D), the amplified beam having a first divergence angle in a first plane (Px) containing the propagation direction and a second divergence angle in a second plane containing the propagation direction and distinct from the first plane, the second divergence angle being distinct from the first divergence angle, and an optical device (3). According to the present invention, the optical device includes a lens (31) arranged to refract the amplified beam into an output beam (5), the lens having a first radius of curvature in the first plane and a second radius of curvature in the second plane, the second radius of curvature being distinct from the first radius of curvature.

Description

[Technical Field]

[0001] The present invention relates generally to the field of optics.

[0002] The present invention more particularly relates to laser systems.

[0003] The invention finds particularly advantageous application in the construction of laser systems based on slab-type gain media. [Background technology]

[0004] A laser system ("light amplification by stimulated emission of radiation") conventionally includes an amplifying medium, e.g., a solid state, designed to emit a spatially and temporally coherent beam of light. Such a beam is often also called a "laser."

[0005] In the case of an amplification medium that does not have rotational symmetry about the propagation axis, the emitted light beam often has astigmatism. This light beam can therefore have different divergence or spread angles in different planes containing the beam's propagation direction. Therefore, a light beam emitted from a solid-state amplification medium that is not rotationally symmetric is often elliptical and / or astigmatic.

[0006] To make this light beam circular (ellipticity close to 1) or simply non-astigmatic and less divergent (collimated), laser systems include optical beam shaping devices. Such optical devices generally require three or four lenses that successively refract the light beam. Some lenses serve to circularize the beam by each changing the beam divergence in a certain direction, while other lenses collimate the beam, making it possible to correct for inherent astigmatism or astigmatism caused by different lenses.

[0007] However, such optical beam shaping devices are expensive, complicated to adjust, and take up a lot of space. Summary of the Invention [Means for solving the problem]

[0008] In this regard, the present invention provides - a solid-state amplifying medium capable of emitting an amplified beam along a propagation direction, the amplified beam having a first divergence angle in a first plane containing the propagation direction and a second divergence angle in a second plane containing the propagation direction and different from the first plane, the second divergence angle being different from the first divergence angle; an optical device including a lens positioned to refract the amplified beam into an output beam, the lens having a first radius of curvature at a first plane and a second radius of curvature at a second plane, the second radius of curvature being different from the first radius of curvature; A laser system including:

[0009] Therefore, the present invention simplifies the optical beam shaping device. In fact, the lenses implemented by the optical device make it possible to simultaneously change two divergence angles of the incident beam. Therefore, the amplified beam can be circularized and collimated with fewer lenses, preferably with one lens.

[0010] Thus, the optical shaping device of the laser system according to the invention is cheap, easy to adjust and takes up little space, even though the degree of adjustment freedom it offers is not very great.

[0011] Thus, in a laser system according to the invention, a complex optical shaping system consisting of at least three or four lenses can be replaced by a single lens, which is therefore manufactured to correct the imperfections of the particular laser system, which limits the risk of misalignment, although it offers less adjustment possibilities.

[0012] Other non-limiting advantageous features of the laser system according to the invention, realized individually or in any technically possible combination, are: - the exit beam has two divergence angles in the first plane and the second plane, respectively, and the first radius of curvature and the second radius of curvature are determined based on the first divergence angle and the second divergence angle so as to satisfy at least one of the following criteria: a difference between the two divergence angles of the exit beam is smaller than a first threshold value; and at least one of the two divergence angles of the exit beam is smaller than a second threshold value; the first radius of curvature and the second radius of curvature are determined so that the exit beam has less astigmatism than the amplified beam; - the amplified beam has a circular cross section perpendicular to the direction of propagation, such that the amplified beam is circular in shape, and the lens is positioned to intersect the circular cross section; - the first plane is perpendicular to the second plane, Between the amplifying medium and the optical shaping device, the amplified beam diverges at a first plane and converges at a second plane; the lens includes a first optical surface defining a first radius of curvature and a second optical surface opposite the first optical surface defining a second radius of curvature; at least one of the first optical surface and the second optical surface extends along a cylindrical surface of revolution; the lens includes a first flat optical surface and a second optical surface opposite the first optical surface, the second optical surface defining a first radius of curvature and a second radius of curvature; the second optical surface extends along the toroidal surface; - the first curvature radius and the second curvature radius are each 1 mm to 1000 mm; the amplified beam comprises a central wavelength and the lens comprises an optical surface whose roughness is less than one-quarter of the central wavelength; - The lens is 100% reflective for wavelengths from 900nm to 1100nm. -5 cm -1 Made of silica with an absorption of less than - the amplified beam has a Gaussian distribution in the transverse direction perpendicular to the propagation direction, - the optical shaping device comprises a lens; - the lens has a thickness in the direction of propagation of 2 mm to 4 mm, - The lenses are made of electronic grade silica, - The lens is 9mm, the amplified beam 2 ~40,000mm 2 - the lens includes at least one coating having a reflectivity at normal incidence of less than 0.1% at 1030 nm; - The amplified beam is a pulsed beam with an emission duration of 100 fs to 20 ns. The solid-state amplifying medium comprises a rectangular parallelepiped crystal, and the lens is positioned opposite the exit edge of the crystal.

[0013] Obviously, the different features, alternatives and embodiments of the invention can be associated with one another according to various combinations, provided that they are not contradictory and mutually exclusive.

[0014] The following description, given by way of non-limiting example with reference to the accompanying drawings, will enable a better understanding of what the invention consists of and how it can be put into practice. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a schematic cross-sectional view in a first plane of a laser system according to the invention; [Figure 2] 2 is a schematic cross-sectional view of the laser system of FIG. 1 in a second plane. [Figure 3] 2 is a schematic cross-sectional view in a first plane of a portion of a light beam generated by the laser system of FIG. 1; [Figure 4] 3 is a schematic diagram of a light beam generated by a laser system, freely propagating in each of the planes of FIGS. 1 and 2 as well as in a transverse plane. [Figure 5] 5 is a schematic diagram of the light beam of FIG. 4 refracted into an output beam by a lens implemented in the laser system of FIG. 1 in accordance with a first embodiment of the present invention. [Figure 6] FIG. 6 is a schematic perspective view of the lens of FIG. 5. [Figure 7] FIG. 2 is a schematic perspective view of a second embodiment of a lens implemented in the laser system of FIG. 1. DETAILED DESCRIPTION OF THE INVENTION

[0016] A laser system 1 according to the present invention is shown in Figures 1 and 2. As shown in Figure 1 or 2, the laser system 1 includes an amplification medium 2 and an optical device 3. The laser system 1 is called a "laser" in the sense that it is capable of generating a high-intensity light beam that is spatially and temporally coherent. More specifically, the laser system 1 may be of any pulse type and based on a crystalline amplification medium. The laser system may be used, for example, for laser cutting.

[0017] The laser system 1 is designed to generate a pulsed light beam with an energy of 10 W to 10 kW at a wavelength varying between 50 kHz and 40 MHz, for example. The emission duration is between 100 fs and 1 ns, for example. The light beam power is between 1 μJ and 10 mJ, for example.

[0018] 1 and 2, the amplifying medium 2 can emit a laser light beam, which will be referred to hereinafter as the amplified beam 4. For that purpose, the amplifying medium 2, which is here solid, is optically pumped to bring the constituent atoms into an excited state. Conventionally, the laser system 1 includes an optical cavity (not shown), which includes, for example, two mirrors, in which the amplifying medium 2 is placed. A precursor beam (not shown) injected into the optical cavity thus passes multiple times through the amplifying medium 2, which generates the amplified beam 4 by pump radiation.

[0019] The gain medium 2 here has a rectangular parallelepiped shape, for example a rectangle. The entrance and exit faces of the gain medium can also be wedge-shaped, i.e. non-parallel, to avoid back propagation within the gain medium 2. The gain medium 2 more specifically has a slab shape, and the precursor beam is injected through the edge of the slab perpendicular to the thickness of the slab, i.e. its smallest dimension. The gain medium 2 has, for example, a width of 5 mm to 30 mm, a length of 5 mm to 30 mm and a thickness of 0.3 mm to 2 mm.

[0020] The amplification medium 2 is made of, for example, neodymium-doped yttrium aluminum garnet (Nd:YAG) or ytterbium-doped yttrium aluminum garnet (Yb:YAG). The amplified beam 4 has a central wavelength at which its intensity is maximum, which is, for example, 1000 nm to 1100 nm. The central wavelength depends on the material from which the amplification medium 2 is made. Thus, for example, in the case of an amplification medium made of Yb:YAG, the central wavelength is 1030 nm, and in the case of an amplification medium made of Nb:YAG, the wavelength is 1064 nm.

[0021] The amplified beam 4 is emitted by the amplifying medium 2 in a propagation direction D, which here corresponds to the Z axis of a cartesian XYZ coordinate system. The width of the incident beam 4 defined along a direction perpendicular to the propagation direction D is, for example, a segment whose intensity at the central wavelength is higher than half the maximum intensity and corresponds to a full width at half maximum; - At the central wavelength, the intensity reaches its maximum intensity e 2 a segment that is divided by, or - Segments whose energy is higher than 86% of the total energy of the incident beam 4 corresponds to the X-axis or Y-axis of the Cartesian XYZ coordinate system.

[0022] In the following, the width of the amplified beam 4 is defined as the full width at half maximum.

[0023] The geometry of the gain medium 2 imparts astigmatism to the amplified beam 4. For gain medium 2 with a rectangular exit edge 21, the divergence at the short side of the edge is driven primarily by the gain of the gain medium, and the divergence at the long side is driven primarily by the radii of curvature of the mirrors that form the optical cavity.

[0024] Here, more specifically, the amplified beam 4 has a first divergence angle Ax in a first plane Px containing the propagation direction D, and a second divergence angle in a second plane Py that also contains the propagation direction D and is different from the first plane Px. The mathematical term "contains" here means that the propagation direction D is contained in, i.e., extends within, the first plane Px and the second plane Py. Here, the first divergence angle Ax is different from the second divergence angle Ay.

[0025] In the following, as shown in Figure 1, a first width Lx of the incident beam 4 is defined as the width of the incident beam 4 along a direction perpendicular to the propagation direction D and contained in a first plane Px. Similarly, as shown in Figure 2, a second width Ly of the incident beam 4 is defined as the width of the incident beam 4 along a direction perpendicular to the propagation direction D and contained in a second plane Px.

[0026] Each divergence angle Ax, Ay is an angle that represents the change in width of the amplified beam 4 within its respective plane Px, Py along the propagation direction D. As shown in Figure 3, the first divergence angle Ax represents the change in the first width Lx, and the second divergence angle Ay represents the change in the second width Ly. Each divergence angle Ax, Ay is defined, for example, by the ISO 11146 standard.

[0027] More specifically, as shown in Figure 3, the first divergence angle Ax is defined here as the half angle measured at the first magnitude Tx of the incident beam 4, i.e., the focus of the amplified beam 4 in the first plane Px, between the first circumference Fx of the amplified beam 4 and the propagation direction D, and the first width Lx is minimum, in the first plane Px. As shown in Figure 3, the first circumference Fx represents the variation of the first width Lx in the first plane Px.

[0028] The second divergence angle Ay is similarly defined here as the half angle measured at the focus of the amplified beam 4 in the second plane Py between the second circumference Fy of the amplified beam 4 and the propagation direction D of the second magnitude Ty of the incident beam 4, i.e., the second width Ly, at a minimum, and the second circumference Fy represents the change in the second width Ly in the second plane Py.

[0029] The amplified beam 4 has astigmatism, and its first magnitude and its second magnitude are spatially separated from each other, for example, they are separated from each other along the propagation direction D by 1 mm to 10,000 mm.

[0030] Due to its astigmatism, the amplified beam 4 has a section perpendicular to the propagation direction D between the amplification medium 2 and the optical device 3 that is generally elliptical.

[0031] Here, as shown in Figure 4, a first plane Px and a second plane Py are defined to be perpendicular to each other. As shown in Figures 1 and 2, the first plane Px here corresponds to the XZ plane of the orthogonal XYZ coordinate system, and the second plane Py corresponds to the YZ plane of the orthogonal XYZ coordinate system.

[0032] The first plane Px and the second plane Py are more specifically defined to correspond to the major and minor axes of the elliptical cross section of the incident beam 4 in transverse planes T1, T2, T3 perpendicular to the propagation direction D.

[0033] 4, the amplified beam 4 has an elliptical shape in a first transverse cross-section T1 with its major axis contained in a second plane Py, and then in a second transverse cross-section T2 and a third transverse cross-section T3 with its major axis contained in the first plane Px. The first transverse cross-section T1 here corresponds to that of the exit edge 21 of the amplification medium 2.

[0034] Here, perpendicular to the propagation direction D, i.e. along transverse directions perpendicular to the propagation direction D, for example along the X and Y axes of a cartesian XYZ coordinate system, the amplified beam 4 has a generally Gaussian distribution of intensity at the central wavelength.

[0035] The optical device 3 is adapted to shape the amplified beam 4 in that it makes it possible to modify the geometrical properties of the amplified beam 4 .

[0036] 1 and 2, the optical device 3 includes a lens 31 arranged along the propagation direction D. The lens 31 is here positioned opposite the exit edge 21 of the amplification medium 2 from which the amplified beam 4 emerges. The lens 31 therefore refracts the amplified beam 4 into an exit beam 5. The exit beam 5 also has a divergence angle in the first plane Px, referred to as the primary divergence angle, and a divergence angle in the second plane Px, referred to as the secondary divergence angle. The divergence angles of the exit beam 5 are defined in the same way as those of the incident beam 4.

[0037] Notably, lens 31 has two different radii of curvature in two different planes. In other words, lens 31 is a bifocal lens. Each of the radii of curvature Rx, Ry is associated with a strictly positive, i.e., non-zero, curvature. Lens 31 is oriented so as to have a first radius of curvature Rx in a first plane Px and a second radius of curvature Ry in a second plane Py.

[0038] By determining the first radius of curvature Rx and the second radius of curvature Ry based on the first divergence angle Ax and the second divergence angle Ay, the lens 31 is adapted to circularize or collimate the output beam 5. Preferably, the lens 31 is adapted to circularize and collimate the output beam 5.

[0039] The effect of lens 31 on amplified beam 4 is shown in FIG. 5 compared to FIG. 4, which shows free propagation of amplified beam 4. In FIG. 4, i.e., without lens 31, amplified beam 4 is elliptical at second transverse cross-section T2 and third transverse cross-section T3 and diverges because first length Lx and second length Ly increase between second transverse cross-section T2 and third transverse cross-section T3. In FIG. 5, output beam 5 is circular in shape as shown at second transverse cross-section T2 and third transverse cross-section T3. Output beam 5 is therefore also astigmatism-free. Furthermore, output beam 5 is collimated because its diameter is substantially equal in the Rayleigh region, e.g., here at second transverse cross-section T2 and third transverse cross-section T3.

[0040] The outgoing beam 5 can therefore be shaped using only the lens 31, which is therefore preferably designed specifically with respect to the shape of the amplified beam 4. The adjustment of the optical device 3 is simple since it here consists of one optical element, namely the lens 31. On the other hand, the design of the lens 31 depends on the amplified beam 4 and thus on the amplifying medium 2.

[0041] The first radius of curvature Rx and the second radius of curvature Ry may be determined to optimize the circularity of the output beam 5, i.e., to make the cross section of the output beam 5 circular in a plane perpendicular to the propagation direction D. The circularity of a laser beam is defined here according to the ISO 11146 standard. A beam is therefore considered to be circular when its ellipticity is higher than 87%.

[0042] The first radius of curvature Rx and the second radius of curvature Ry are therefore determined so as to minimize the difference between the primary and secondary divergence angles of the output beam 5. In practice, the radii of curvature Rx, Ry of the lens 31 are therefore determined so that the difference between the primary and secondary divergence angles is less than a first threshold value, which is, for example, less than 0.1 mrad.

[0043] The first and second radii of curvature Rx and Ry are determined so as to minimize the divergence of the output beam 5, i.e., so as to minimize the spread of the output beam 5. In other words, the first and second radii of curvature Rx and Ry are determined so as to minimize the primary divergence angle or the secondary divergence angle. Preferably, the radii of curvature Rx and Ry of the lens 31 are determined so as to minimize both the primary and secondary divergence angles. In practice, the radii of curvature Rx and Ry of the lens 31 are therefore determined so that the primary and / or second divergence angles are less than a second threshold value. The second threshold value is, for example, 0.1 μrad to 2 mrad.

[0044] Naturally, the values ​​of the radii of curvature Rx, Ry also depend on the optical index of the lens 31. The lens 31 can therefore be designed in terms of a focal length, which is therefore converted into a radius of curvature, for example according to the following formula: R=f·(n−1), where R is the radius of curvature, F is the desired focal length and n is the optical index of the lens.

[0045] Furthermore, lens 31 makes the exit beam 5 less astigmatic than the amplified beam 4 .

[0046] 4, the amplified beam 4 has astigmatism, but it has a circular cross section S perpendicular to the propagation direction D, where the amplified beam 4 is circular. Before and after this circular cross section S, the incident beam 4 is elliptical.

[0047] 5, it is notable that the lens 31 is positioned so as to intersect with the circular cross section S. This can improve the combined collimating and circularizing effect of the lens 31. The lens 31 is here designed to operate with the circular cross section S.

[0048] 1, 2, and 5, between the gain medium 2 and the lens 31, the amplified beam 4 diverges in a first plane Px and converges in a second plane Py. Such amplified beams are typically generated by slab-type laser systems. In these systems, the short side of the slab edge is contained in the first plane Px, and the long side of the slab edge is contained in the second plane Py.

[0049] As shown in Figure 4, at the exit of the amplification medium 2, the first width Lx then increases along the propagation direction D, while the second width Ly decreases. As diagrammed in Figure 4, the circular cross section S therefore corresponds to a plane perpendicular to the propagation direction D, in which the first width Lx is equal to the second width Ly. Here, the amplified beam 4 is therefore circular with the circular cross section S. Upstream of the circular cross section S, the incident beam 4 is elliptical with its major axis lying in the second plane Py, and downstream of the circular cross section S, the incident beam 4 is elliptical with its major axis lying in the first plane Px.

[0050] 5, in order to circularize and collimate output beam 5, the first radius of curvature Rx is associated with a positive focal length in that the associated image focal point is located downstream of lens 31 along the propagation direction, i.e., on the side of output beam 5. In contrast, the second radius of curvature Ry is associated with a negative focal length in that the associated image focal point is located upstream of lens 31 along the propagation direction, i.e., on the side of amplified beam 4.

[0051] Thus, with lens 31 oriented to have a first radius of curvature Rx in a first plane Px and a second radius of curvature Ry in a second plane Py and positioned within circular cross section S, output beam 5 is now circular and collimated. In Figure 5, the diameter of output beam 5 is therefore generally constant up to third cross section T3 in the Rayleigh region.

[0052] 1 and 2, the lens 31 includes two opposite optical surfaces. More specifically, the lens 31 includes a first optical surface 32 that is illuminated by the amplified beam 4 and a second optical surface 33 from which the output beam 5 is emitted. In other words, the first optical surface 32 is directed towards the amplification medium 2, and the second optical surface 33 is directed away from the amplification medium 2. Here, the optical surfaces 32, 33 are arranged perpendicular to the propagation direction D. The lens 31 is configured so that the amplified beam 4 is projected within 0.2 mm of the first optical surface 32. 2 ~40,000mm 2 , for example 9mm 2 ~10,000mm 2 Advantageously, the lens 31 is arranged to illuminate a surface of e.g. 2 ~100mm 2 The lens has smaller optical surfaces 32, 33, which makes the lens cheaper and smaller.

[0053] The thickness of the lens 31 is, for example, 2 mm to 4 mm. The thickness of the lens 31 may also correspond to its size along the propagation direction D or the minimum distance between the first optical surface 32 and the second optical surface 33.

[0054] Lens 31 also includes a peripheral edge 34 connecting optical surfaces 32, 33. Peripheral edge 34 may have a square profile or a circular profile perpendicular to the propagation of amplified beam 4, for example, as shown in FIGS.

[0055] In the first embodiment shown in Figures 5 and 6, each optical surface 32, 33 defines one of radii of curvature Rx, Ry respectively.

[0056] Thus, here, the first optical surface 32 defines a first radius of curvature Rx, and the second optical surface 33 defines a second radius of curvature Ry. This means that the intersection of the first optical surface 32 with the first plane Px defines an arc of a circle having a radius of curvature equal to the first radius of curvature Rx. Similarly, this means that the intersection of the second optical surface 32 with the second plane Px defines an arc of a circle having a radius of curvature equal to the second radius of curvature Ry.

[0057] Of course, equivalently, first optical surface 32 may define a second radius of curvature Ry and second optical surface 33 may define a first radius of curvature Rx.

[0058] Advantageously, in this embodiment, the lens 31 can be manufactured simply, cheaply and with high precision: the radii of curvature Rx, Ry are therefore designed with tolerances of less than 1%.

[0059] 6, each optical surface 32, 33 now extends along a cylindrical surface of revolution. In other words, the first optical surface 32 corresponds to a portion of the cylindrical surface of revolution having a radius equal to the first radius of curvature Rx. Similarly, the second optical surface 33 corresponds to a portion of the cylindrical surface of revolution having a radius equal to the second radius of curvature Ry.

[0060] Here, the first plane Px is perpendicular to the second plane Py, and the optical surfaces 32 and 33 extend along cylindrical surfaces of revolution whose axes are oriented orthogonal to each other. In other words, the first optical surface 32 corresponds to a portion of the cylindrical surface of the cylindrical surface of revolution whose axis is included in the second plane Py. Similarly, the second optical surface 32 corresponds to a portion of the cylindrical surface of the cylindrical surface of revolution whose axis is included in the first plane Px.

[0061] The aforementioned cylindrical surface portions here depend on the shape of the peripheral edges 34, so that they are, for example, square or circular.

[0062] As an alternative to this first embodiment, one of the optical surfaces may extend along a cylindrical surface of revolution, and the other optical surface extends along a spherical surface.

[0063] In this first embodiment, the first optical surface 32 is convex and the second optical surface 33 is concave in order to shape the amplified beam 4 shown in Figures 1 and 2 (diverging in a first plane Px and converging in a second plane Py). Of course, equally, if the first optical surface 32 defines a second radius of curvature Ry and the second optical surface 33 defines a first radius of curvature Rx, then the first optical surface 32 is concave and the second optical surface is convex.

[0064] In this first embodiment, lens 31 has a mid-plane PM located midway between optical surfaces 32, 33. This mid-plane PM is the plane that most closely matches optical surfaces 32, 33, for example, by linear regression. Preferably, mid-plane PM of lens 31 blends with the circular cross section S of incident beam 4, as shown in Figure 5. This can improve the combined collimating and circularizing effect of lens 31.

[0065] In a second embodiment shown in FIG. 7, one of the optical surfaces 32, 33 is flat and the other optical surface 32, 33 defines a first radius of curvature Rx and a second radius of curvature Ry.

[0066] 7, the first optical surface 32 is flat, and the second optical surface 33 defines both a first radius of curvature Rx and a second radius of curvature Ry, meaning that the intersection of the second optical surface 33 with the first plane Px defines an arc of a circle having a radius of curvature equal to the first radius of curvature Rx, and the intersection of the second plane Py defines an arc of a circle having a radius of curvature equal to the second radius of curvature Ry.

[0067] Advantageously, in this second embodiment, the lens 31 is placed so that the second optical surface 33 intersects the circular cross section S. Preferably, the lens 31 is placed so that the circular cross section S merges with the mid-plane of the second optical surface 33. The mid-plane of the second optical surface 33 is, for example, a plane tangent to the second optical surface 33 at the center of the second optical surface 33, or also a plane that best fits the second optical surface 33 by linear regression.

[0068] Therefore, in this second embodiment, the lens 31 generates almost no astigmatism because the two radii of curvature Rx and Ry are in the same plane.

[0069] 7, the second optical surface 33 extends along a toroidal surface. The second optical surface 33 therefore corresponds to a portion of a surface obtained by rotating, for example, a circle having a radius equal to the first radius of curvature Rx, around a straight line located at a distance equal to the second radius of curvature Ry. Said portion here depends on the shape of the peripheral edge 34, for example a square or circular shape.

[0070] In this second embodiment, in order to shape the amplified beam 4 shown in Figures 1 and 2 (diverging in the first plane Px and converging in the second plane Py), the second optical surface 33 is therefore both convex and concave. More specifically, the second optical surface 33 is convex in the first plane Px and concave in the second plane Py. The second optical surface therefore extends along a surface portion of the open annulus that is located opposite the axis of rotation of the annulus.

[0071] The first optical surface 32 is preferably perpendicular to the direction of propagation D.

[0072] In either embodiment, lens 31 is made here of silica. Lens 31 could also be made of other optical glasses, such as flint glass or crown glass. Lens 31 is made here of electronic-grade silica (SiO2). This reduces inclusions that may be present in lens 31 and contribute to its heating when illuminated by amplified beam 4. Preferably, the lens has a low OH ion content, for example less than 1000 ppm, so that the lens absorbs little infrared radiation, which limits its heating.

[0073] Here, the lens 31 has a 10 Hz reflectance for wavelengths of 900 nm to 1100 nm. -5 cm -1 The lens 31 is made of silica, which has an absorption of less than ppm. Since the infrared range is the preferred operating range of laser systems, it is advantageous that the lens 31 has low absorption in this range. Here, therefore, heating of the lens 31 is greatly limited when the amplified beam 4 is within the above-mentioned wavelength range.

[0074] The lens 31 is manufactured here using computer numerically controlled machining, also known as "CNC" machining, which allows for the creation of complex optical surfaces, such as toroidal surfaces like those in the second embodiment, with high precision. Manufacturing by computer numerically controlled machining allows for the shaping of spherical, aspherical, or freeform surfaces, among others. After machining, the optical surfaces 32, 33 are polished to a roughness of less than one-quarter of the central wavelength. According to the MIL-PRF-13830B standard, the optical surfaces 32, 33 are polished to a scratch and dent ratio of 10 to 20. *** Do you think the French translation of the parameters and values ​​is correct? ***

[0075] The lens 31 may also be treated by depositing a coating on its optical surfaces 32, 33. The lens 31 may, for example, include one of the following coatings: anti-reflective, nanostructured coating. Preferably, the anti-reflective coating has a reflectivity at normal incidence of less than 0.1% at 1030 nm. The coating is deposited after polishing.

[0076] The present invention is in no way limited to the described and illustrated embodiments, and a person skilled in the art will know how to apply any variant according to the present invention. For example, the amplified beam may diverge in both the first and second planes (between the amplifying medium and the optical device). This is the case, for example, when the amplifying medium corresponds to that of a laser diode. For such an amplified beam, the lens is adapted to have two positive focal lengths. If the divergence of such an amplified beam is not the same in the first or second plane, it also preferably has a circular cross section, at which the lens is positioned. If the amplifying medium corresponds to that of a laser diode, the radius of curvature is, for example, between 1 mm and 1000 mm.

Claims

1. a solid-state amplifying medium (2) capable of emitting an amplified beam (4) along a propagation direction (D), said amplified beam (4) having a first divergence angle (Ax) in a first plane (Px) containing said propagation direction (D) and a second divergence angle in a second plane (Py) containing said propagation direction (D) and different from said first plane (Px), said second divergence angle being different from said first divergence angle (Ax); - optical device (3) and wherein the optical device (3) includes a lens (31) arranged to refract the amplified beam (4) into an output beam (5), the lens (31) having a first radius of curvature (Rx) at the first plane (Px) and a second radius of curvature (Ry) at the second plane (Py), the second radius of curvature (Ry) being different from the first radius of curvature (Rx).

2. The output beam (5) has two divergence angles in the first plane (Px) and the second plane (Py), respectively, and the first radius of curvature (Rx) and the second radius of curvature (Ry) are determined based on the first divergence angle (Ax) and the second divergence angle in accordance with the following criteria: the difference between the two divergence angles of the exit beam (5) is less than a first threshold value; at least one of the two divergence angles of the exit beam (5) is smaller than a second threshold value; The laser system (1) according to claim 1, wherein the laser system (1) is determined to satisfy at least one of the following conditions.

3. 3. The laser system (1) of claim 1 or 2, wherein the first radius of curvature (Rx) and the second radius of curvature (Ry) are determined such that the output beam (5) has less astigmatism than the amplified beam (4).

4. 4. The laser system (1) of claim 1, wherein the amplified beam (4) has a circular cross section (S) perpendicular to the propagation direction (D) such that the amplified beam (4) is circular in shape, and the lens (31) is positioned to intersect the circular cross section (S).

5. The laser system (1) according to any one of claims 1 to 4, wherein the first plane (Px) is perpendicular to the second plane (Py).

6. 6. The laser system (1) according to claim 1, wherein between the amplifying medium (2) and the optical shaping device (3), the amplified beam (4) diverges at the first plane (Px) and converges at the second plane (Py).

7. The lens (31) a first optical surface (32) defining said first radius of curvature (Rx); a second optical surface (33) opposite said first optical surface (32) and defining said second radius of curvature (Ry); The laser system (1) according to any one of claims 1 to 6, comprising:

8. 8. The laser system (1) of claim 7, wherein at least one of the first optical surface (32) and the second optical surface (33) extends along a cylindrical surface of revolution.

9. The lens (31) a first flat optical surface (32); a second optical surface (33) opposite said first optical surface (32) and defining said first radius of curvature (Rx) and said second radius of curvature (Ry); The laser system (1) according to any one of claims 1 to 6, comprising:

10. 10. The laser system (1) of claim 9, wherein the second optical surface (33) extends along a toroidal surface.

11. The laser system (1) according to any one of the preceding claims, wherein the first radius of curvature (Rx) and the second radius of curvature (Ry) are each comprised between 1 mm and 1000 mm.

12. 12. The laser system (1) of claim 1, wherein the amplified beam (4) comprises a central wavelength and the lens (31) comprises optical surfaces (32, 33) whose roughness is less than one-quarter of the central wavelength.

13. The lens (31) has a 10 Hz response for wavelengths between 900 nm and 1100 nm. －５ cm －１ 13. The laser system (1) according to any one of claims 1 to 12, made of silica having an absorption of less than 1000 .mu.m.

14. The laser system (1) according to any one of the preceding claims, wherein the amplified beam (4) has a Gaussian distribution in a transverse direction perpendicular to the propagation direction (D).

15. The laser system (1) according to any one of claims 1 to 14, wherein the optical shaping device (3) consists of the lens (31).

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