Scanning system for multiple laser sources

Abstract

A scanning system (1) includes : an expander assembly (2) comprising a first and a second objective optics (21, 22), which are configured to receive, respectively, a first and a second beam (B1, B2) of a laser type; a combination assembly (5) configured to receive the first and the second beam (B1, B2) from the first and from the second objective optics (21, 22), respectively, and to couple the first and the second beam (B1, B2), so as to generate a combined beam (C); and an electrically controllable deflection assembly (3), configured to deflect the combined beam (C). The expander assembly (2) further comprises an image optics (23), which is arranged optically downstream of the deflection assembly (3), so as to receive the combined beam (C) deflected by the deflection assembly (3). The image optics (23) and the first objective optics (21) form a first beam expander (21, 23), which is configured to expand the first beam (B1); the image optics (23) and the second objective optics (22) form a second beam expander (22, 23), which is configured to expand the second beam (B2).

Description

[0001] "SCANNING SYSTEM FOR MULTIPLE LASER SOURCES"

[0002] Cross-Reference To Related Applications

[0003] This patent appl ication claims priority from Italian patent application no . 102024000000792 filed on January 17 , 2024 , the entire disclosure of which is incorporated herein by reference .

[0004] Technical Field

[0005] The present invention relates to a scanning system for multiple laser sources .

[0006] Background

[0007] As is well known, material processing applications using laser sources ( known as " laser processing" ) favour the use of high-speed beam scanning systems that comprise a deflection assembly and a focusing assembly for the aforesaid laser beams . The deflection assembly, known as a " scan head" , typically comprises a pair of galvanometric mirrors configured to rotate about mutually perpendicular axes , deflecting a laser beam ( or simply "beam" ) with respect to two corresponding directions . The focusing assembly typically comprises a chain of lenses configured to focus , for a predetermined wavelength range , the beam exiting the deflection assembly on a fixed focal plane . In the case of a static focusing assembly, this is commonly known as the " F-Theta lens" ; alternatively, a similar result may be obtained by moving some of the lenses that make up said chain in order to create focal planes moving in the longitudinal direction .

[0008] The diameter of the beam obtainable in the focus ( known as the " spot" ) is inversely proportional to the diameter of the beam entering the focusing assembly . When processing materials , it is preferable for the power density in the focus to be as high as possible, minimising the persistence time of the beam on a given portion of the material and thus optimising processing in terms of quality and speed. To this end, energy efficiency considerations make it preferable to minimise the spot than to increase the average power of the laser source. Furthermore, applications such as marking identification marks (e.g. QR codes) on a microscopic scale may require a high degree of line accuracy, which may be achieved by spots as close to the diffraction limit as possible. An expansion block (known as a "beam expander") is therefore used upstream of the scanning system, which expands and collimates the beam bringing it, from the size at the source exit, to the appropriate diameter at the entrance of the deflection assembly, and hence of the focusing assembly.

[0009] Nowadays, laser sources used for processing materials may also comprise semiconductor lasers (known as "laser diodes") , which typically emit beams characterised by values of a characteristic parameter known as "beam parameter product" (BPP) that are high compared to the theoretical limit of an ideal source at the same wavelength, indicating low quality. The quality of a beam is typically quantified in terms of the parameter known as M2, which represents the ratio between the BPP of the beam emitted by the source under consideration and the theoretical limiting BPP of an ideal source at the same wavelength. This parameter M2has a minimum value of 1 and increases as the quality of the beam decreases (e.g. M2>10) . Such a beam with M2greater than 1 may create a spot that, as the parameter M2increases, increasingly differs from the so-called diffraction limit, imposing relatively large beam diameters at the entrance of the scanning system in order to meet the power density requirements in the focal plane. Such a problem may also arise for optical fibre-coupled laser sources ("fibre- delivered" sources) , particularly if the fibre is multimode with a large diameter.

[0010] However, the feasible sizes and shapes of galvanometric mirrors place a limit on the diameters of the beams entering the deflection unit (e.g. 30mm) . In addition, the use of large mirrors, characterised by high inertia - which reduces the maximum acceleration that can be imparted to them - as well as by high production costs, may significantly reduce the processing speed, precluding their use in more demanding applications .

[0011] In addition, it is a trend in the industry to combine a main laser source with an auxiliary laser source, typically with different wavelengths, in order, for example, to carry out specific processing depending on the absorption of radiation by the materials being processed. However, multiple wavelength scanning systems, especially if clearly separated (e.g. one source in the visible and one in the infrared) , may present additional complications in terms of obtainable spots due to the possible difference in quality of the two beams, as well as wavelength-dependent optical aberrations of the focusing assembly (phenomena that altogether result in focal plane shifts between the two beams, or "focus shifts", and different spot sizes) , which may not be compensable without loss of focus resolution of at least one of the two sources.

[0012] Summary

[0013] It is therefore an aim of the present invention to provide a solution which at least in part overcomes the disadvantages and limitations of the prior art.

[0014] According to the present invention, a laser scanning system is presented, as defined in the appended claims. Brief Description of the Figures

[0015] To better understand the present invention preferred embodiments thereof will now be described, for merely exemplary and non-limiting purposes , with reference to the accompanying drawings , wherein :

[0016] Figure 1 shows a block diagram of a principle diagram of an optical chain of the present scanning system;

[0017] Figure 2 shows a block diagram of a first embodiment of the present invention; and

[0018] Figure 3 shows a block diagram of a second embodiment of the present invention .

[0019] Description of Embodiments

[0020] With reference to Figure 1 , a scanning system is denoted as a whole by the number 1 and comprises an expander assembly 2 , a deflection assembly 3 and a focusing assembly 4 arranged optically downstream of the deflection assembly 3 . The scanning system 1 is configured to operate on laser beams ( or simply "beams" ) generated by a first source S I and a second source S2 , and has a first input I I and a second input 12 .

[0021] The first source S I emits a corresponding first beam Bl and the second source S2 emits a corresponding second beam B2 , the electromagnetic radiation of the first beam Bl being distinguished from the electromagnetic radiation of the second beam B2 by at least one wave characteristic, such as wavelength, polarisation or both . In a non-limiting embodiment , the first source S I is , for example , a semiconductor laser, emitting radiation in the visible spectrum, while the second source S2 is , for example , a fibre-optic or solid-state laser, emitting radiation in the infrared spectrum, or is also a low-quality source such as a multimode fibre-optic coupled laser source . The first and the second inputs II, 12 are configured to receive the first and the second beams Bl, B2 respectively.

[0022] The expander assembly 2 comprises a first objective optics 21, a second objective optics 22 and an image optics 23. In detail, the first objective optics 21 is optically coupled to the first input II and thus receives the first beam Bl, while the second objective optics 22 is optically coupled to the second input 12 and receives the second beam B2. Furthermore, the first beam Bl exiting the first objective optics 21 is propagated along a first optical axis 01, while the second beam B2 leaving the second objective optics 22 is propagated along a second optical axis 02, e.g. transverse to the first optical axis 01. In more detail, the first and the second objective optics 21, 22 are optically arranged upstream of the deflection assembly 3, while the image optics 23 is optically arranged downstream of deflection assembly 3 and, in particular, is optically comprised between the deflection assembly 3 and the focusing assembly 4. The first objective optics 21 and image optics 23 form a first expansion branch of the scanning system 1 for the first beam Bl, while the second objective optics 22 and image optics 23 form a second expansion branch of scanning system 1 for the second beam B2.

[0023] The scanning system 1 also comprises a combination assembly 5. The combination assembly 5 is optically arranged downstream of the first and the second objective optics 21, 22 and optically upstream of the deflection assembly 3. The combination assembly 5 is configured to receive the first and the second beams Bl, B2 from the first and the second objective optics 21, 22 respectively, and to couple them in such a way that they are propagated, downstream of the combination assembly 5, parallel to the same direction, e.g. collinear with the first optical axis 01 . The deflection assembly 3 thus receives as input a combination of the first and the second beams Bl , B2 . This combination of beams is referred to as a combined beam C . In a non-limiting embodiment , the combined beam C is a spatial superposition of the first and the second beams Bl , B2 .

[0024] The deflection assembly 3 comprises a pair of galvanometric mirrors , speci fically a first galvanometric mirror 31 and a second galvanometric mirror 32 , configured to rotate about mutually perpendicular axes . In particular, the rotation of the first and the second galvanometric mirrors 31 , 32 defines a solid angle within which the combined beam C can be deflected with respect to a main optical axis 0. Planes perpendicular to the main optical axis 0 and intersecting the solid angle define respective scanning planes o f the scanning system 1 . Each of the first and the second galvanometric mirrors 31 , 32 is set in motion by a corresponding galvanometric motor, not shown in the accompanying figures . The image optics 23 therefore receives the combined beam C deflected by the deflection assembly 3 as an input .

[0025] The focusing assembly 4 comprises a chain of lenses that create , on a focal plane ( e . g . fixed) downstream of the scanning system 1 , a focus F of the combined beam C exiting the image optics 23 . The focal plane of focusing as sembly 4 corresponds to one of the above-mentioned scanning planes , defining a laser processing plane of the scanning system 1 .

[0026] Therefore , in the scanning system 1 , the first beam Bl is propagated along a respective optical path meeting sequentially the first obj ective optics 21 , the combination assembly 5 , the deflection assembly 3 , the image optics 23 and the focusing assembly 4 ; the second beam B2 is propagated along a respective optical path meeting sequentially the second obj ective optics 22 , the combination assembly 5 , the deflection assembly 3 , the image optics 23 and the focusing assembly 4 . Irrespective of the de flection generated by the deflection assembly 3 , the first and the second beams Bl , B2 undergo , along their respective optical paths in the scanning system 1 , an expansion of their respective diameters through the expander assembly 2 and, more particularly, respectively, through the pair formed by the first obj ective optics 21 and the image optics 23 and through the pair formed by the second obj ective optics 22 and the image optics 23 . These pairs form, respectively, a corresponding first beam expander for the first beam Bl and a corresponding second beam expander for the second beam B2 . The first and the second beam expanders actually share the same second optics of the respective pairs , coinciding with the image optics 23 of the expander assembly 2 . Furthermore , the first and the second beam expanders may have di f ferent magni fication ratios depending on the respective relationships between the dioptric powers of the optics of each pair .

[0027] The si ze of the first beam Bl in the focus F, denoted by " first spot" , and the si ze of the second beam B2 in the focus F, denoted by " second spot" , depend on the respective diameters obtained by the first and the second beam expanders , i . e . the diameters that the first and the second beams Bl , B2 have downstream of the image optics 23 . The dioptric power of the focusing assembly 4 thus defines , having the beam quality and the wavelength for the first and the second source S I , S2 fixed, the first spot and the second spot .

[0028] With this in mind, in the scanning system 1 , the combination assembly 5 and def lection assembly 3 are optically comprised in the expander assembly 2 and, in particular, between the first obj ective optics 21 and the image optics 23 and between the second obj ective optics 22 and the image optics 23 . The ef fect of the expansion of the beam diameters along the respective optical paths in the scanning system 1 can be appreciated in the Figures for the embodiments described below, in which the first and the second beams Bl , B2 pass through the combination as sembly 5 and the deflection assembly 3 in a divergence and / or convergence condition with respect to the first optical axis 01 , the second optical axis 02 and with respect to the main optical axis 0.

[0029] The scanning system of the present invention thus makes it possible to use smaller optical elements for the combination assembly and the deflection assembly than a scanning system in which the beams from the sources are already expanded to the diameters required to create the desired spots , with the same power density obtainable in the focus and the same source characteristics . In detai l , it is possible to use galvanometric mirrors with dimensions that guarantee high performance in terms of scanning speed and, at the same time, obtain spots to achieve power densities suitable for the speci fic processing . In addition, the present scanning system makes it possible to minimise the ef fects of chromatic and / or spherical aberrations of the focusing assembly by appropriately si zing the magnification ratio of the first and the second beam expanders . By also providing longitudinal movement of the first and / or the second obj ective optics 21 , 22 , it is possible to achieve dynamic and separate spot adj ustment of the respective sources according to the required processing conditions and / or for better superposition in the focal plane , e . g . for three-dimensional processing applications .

[0030] Figure 2 shows a first embodiment of the scanning system 1 and, in particular, the expander assembly 2 .

[0031] The first source S I in Figure 2 forms an emission point Pl of the first beam Bl ( e . g . located on the exit face of an optical fibre , or at any rate in the so-called "waist" of the radiation) , which is propagated along the first optical axis 01 with a first wavelength Xi, and comprises a corresponding conditioning optics 11 that brings the first beam Bl to a condition of substantial collimation with a first diameter DI . Similarly, the second source S2 forms an emission point P2 of the second beam B2 , which is propagated along the second optical axis 02 with a second wavelength X2 di f ferent from the first wavelength Xi , and comprises a corresponding conditioning optics 12 that brings the second beam B2 to a condition of substantial collimation with a second diameter D2 . The first diameter D2 may be di f ferent from the second diameter D2 , e . g . D2<D1 .

[0032] The first and the second obj ective optics 21 , 22 of the scanning system 1 of Figure 2 each comprise a chain of lenses with negative dioptric power, configured to make the first and the second beams Bl , B2 diverge , respectively, starting from the respective first and second diameters DI , D2 , along the respective optical paths . For example , the chains of lenses of the first and the second obj ective optics 21 , 22 may each comprise at least one plano-concave lens .

[0033] The combination assembly 5 of the scanning system 1 of Figure 2 comprises a dichroic mirror whose faces (not shown in detail ) hit by the radiation are covered with a coating configured to transmit the first wavelength Xi and to reflect the second wavelength X2 , when positioned at an angle of , for example , 45 ° to the first and the second optical axes 01 , 02 . The combined beam 0 is propagated along the first optical axis 01 and is formed by the spatial superposition of the first and the second beams Bl , B2 .

[0034] The image optics 23 of the scanning system 1 of Figure 2 comprises a chain of lenses with positive dioptric power and is configured to bring the combined beam 0 to a condition of substantial collimation . When exiting the optical image 23 , the first and the second beams Bl , B2 are substantially collimated and have a first expanded diameter DEI and a second expanded diameter DE2 , respectively . The first expanded diameter DEI is larger than the first diameter DI ; the second expanded diameter DE2 is larger than the second diameter D2 . For example , the chain of lenses of the image optics 23 may comprise at least one plano-convex lens . The expander assembly 2 of the scanning system 1 of Figure 2 therefore comprises a first and a second beam expander both of the so-called Galilean type .

[0035] As anticipated, the relationship between the first and the second expanded diameter DEI , DE2 may be calibrated by appropriately selecting the magni fication ratios of the first and the second beam expanders , i . e . by selecting the dioptric power of the first and the second obj ective optics 21 , 22 , respectively, according to the desired spot characteristics for the first and the second beams Bl , B2 in focus F . In addition, the first and the second obj ective optics 21 , 22 , may be moved along their respective optical axes to dynamically and separately adj ust the depth of field of the first and the second beams Bl , B2 around the focus F; furthermore , the focusing assembly 4 may be moved along the main optical axis 0. The focusing assembly 4 of Figure 2 comprises , for example , an F-Theta lens , optionally mounted on a motorised mount for longitudinal movements . As can be seen in Figure 2, when crossing the expander assembly 2, and therefore the combination assembly 5 and the deflection assembly 3, the first and the second beams Bl, B2 are both diverging. The first and the second beam expanders may be selected such that the divergences of the first and the second beams Bl, B2 are such that the first and the second beams Bl, B2 respect the dimensional constraints imposed by the first and the second galvanometric mirrors 31, 32 of the deflection assembly 3, which in turn may be chosen to achieve desired performance in terms of scanning speed. For example, the divergences of the first and the second beams Bl, B2 may be such that each of the first and the second beams Bl, B2 affects the first and the second galvanometric mirrors 31, 32 by intercepting at the most, and without loss of power (i.e., without the beams being cut by the outline of the mirrors) , approximately 70% of the maximum size of the first and the second galvanometric mirrors 31 , 32.

[0036] Figure 3 shows a second embodiment of the scanning system 1 and, in particular, of the expander assembly 2. The embodiment of Figure 3 is described below with reference to the differences from the embodiment of Figure 2.

[0037] In detail, the first and the second objective optics

[0038] 21, 22 of the scanning system 1 of Figure 3 each comprise a chain of lenses with positive dioptric power, such that, downstream of the first and the second objective optics 21,

[0039] 22, the first and the second beams Bl, B2 are convergent. Furthermore, each chain of lenses of the first and the second objective optics 21, 22 is configured to condition the respective first and the second beams Bl, B2 coming, e.g. under divergence conditions, from the respective first and second sources SI, S2. For example, the chains of lenses of the first and the second objective optics 21, 22 each comprise a doublet.

[0040] The image optics 23 comprises a chain of lenses with positive dioptric power and is configured to basically collimate the first and the second beams Bl, B2, and then the combined beam C; for this purpose, the image optics 23 may comprise, for example, a plano-convex lens. The expander assembly 2 of the scanning system 1 of Figure 3 therefore comprises a first and a second beam expander both of the so- called Keplerian type. These first and second beam expanders are configured to obtain respective expanded diameters of the first and the second beams Bl, B2 starting from the respective diameters with which the first and the second beams Bl, B2 hit the respective first and second objective optics 21, 22.

[0041] The chain of lenses of the optical image 23 of Figure 3 also comprises at least one focusing lens to converge the combined beam C into the focus F, e.g. a plano-convex lens and / or an aspherical lens. In other words, in the scanning system 1 in Figure 3, the image optics 23 integrates the function of the focusing assembly 4. In a non-limiting manner, the image optics 23may also be moved along the main optical axis 0, in order to implement, e.g., three- dimensional processing.

[0042] As can be seen in Figure 3, the first and the second beams Bl, B2, when crossing the expander assembly 2, form an intermediate focus FM arranged, for example, between the combination assembly 5 and the deflection assembly 3. The first and the second beams Bl, B2 are therefore: in a condition of convergence between the respective first and second objective optics 21, 22 and the intermediate focus FM, through the combination assembly 5; and in a condition of divergence optically downstream of the intermediate focus FM, i.e. through the deflection assembly 3. For practical purposes, the embodiment of Figure 3 therefore has the same advantages as the embodiment of Figure 2.

[0043] Finally, it is clear that modifications and variations may be made to what has been described and illustrated here without thereby departing from the scope of the present invention, as defined in the attached claims.

[0044] For example, the combination assembly may comprise a wavelength-sensitive element other than the dichroic mirror. The first and the second sources may emit radiation at the same wavelength, but with different polarisations (e.g. both linear and orthogonal to each other) ; the combining assembly may be a polarisation-sensitive element (such as a polarising cube or plate) , rather than wavelength-sensitive.

[0045] The combined beam exiting the combination assembly may be different from a spatial superposition of the first and the second beams: for example, the combined beam may be formed by a flanking, with partial superposition, of the first and the second beams; or, the combined beam may be a flanking - e.g. with symmetry with respect to the optical axis with respect to which the combined beam is propagated - of the first and the second beams.

[0046] The scanning system may also be configured to operate with more than two laser sources. For example, the combination assembly may comprise a sequence of dichroic mirrors or a sequence of dichroic mirrors and polarisationsensitive elements. At the same time, each source is optically coupled, through a respective input of the scanning system, to a respective objective optics. It is therefore possible to have a number of beam expanders equal to the number of sources; the beam expanders share the same image optics .

[0047] The sources may be coupled to the inputs of the scanning system in a di f ferent manner from what is shown, e . g . by using one or more deflection mirrors (not shown) . More generally, the sources may be lasers of a di f ferent nature , spectral characteristics and / or spatial qualities than those described . For example , the sources may be lasers with spatial qualities close to single-mode (M2<2 ) , such as fibre lasers .

[0048] Unlike what has been described, the deflection assembly may comprise a single galvanometric mirror configured to rotate about a single axis or about two mutually orthogonal axes .

[0049] Finally, the characteristics of the expander assemblies of the di f ferent embodiments described so far may be combined to achieve similar performance results . For example , it is possible to integrate the conditioning functions of the sources into the respective obj ective optics of the respective Galilean-type beam expanders ; or, it is possible to separate the conditioning functions of the respective sources and the convergence functions of the obj ective optics of the respective Keplerian-type beam expanders shown . It is also possible to use obj ective optics with negative dioptric power for some sources and obj ective optics with positive dioptric power for other sources , resulting in Gali lean and Keplerian beam expanders in the same scanning system . In addition, the imaging optics may or may not incorporate the beam focusing function on the laser processing plane and / or may or may not be longitudinally moved .

Claims

CLAIMS1. Scanning system (1) comprising:- an expander assembly (2) comprising a first and a second objective optics (21, 22) , which are configured to receive, respectively, a first and a second beam (Bl, B2) of a laser type;- a combination assembly (5) configured to receive the first and the second beam (Bl, B2 ) from the first and from the second objective optics (21, 22) , respectively, and to couple the first and the second beam (Bl, B2) , so as to generate a combined beam (C) ; and- an electrically controllable deflection assembly (3) , configured to deflect the combined beam (C) , wherein the expander assembly (2) further comprises an image optics (23) , which is arranged optically downstream of the deflection assembly (3) , so as to receive the combined beam (C) deflected by the deflection assembly (3) ; and wherein the image optics (23) and the first objective optics (21) form a first beam expander (21, 23) , which is configured to expand the first beam (Bl) ; and wherein the image optics (23) and the second objective optics (22) form a second beam expander (22, 23) , which is configured to expand the second beam (B2 ) .

2. Scanning system (1) according to claim 1, further comprising a focusing assembly (4) , arranged optically downstream of the image optics (23) and configured to generate a focus (F) of the combined beam (C) .

3. Scanning system (1) according to the preceding claim, wherein the image optics (23) has a respective optical axis (0) ; and wherein the focusing assembly (4) is movable along the optical axis (0) of the image optics (23) .

4. Scanning system (1) according to claim 1, whereinthe image optics (23) is configured to generate a focus (F) of the combined beam (C) .

5. Scanning system (1) according to the preceding claim, wherein the image optics (23) is movable along a respective optical axis (0) .

6. Scanning system (1) according to any one of the preceding claims, wherein the first and the second objective optics (21, 22) have a negative dioptric power; and wherein the image optics (23) has a positive dioptric power, such that the first and the second beam expander (21, 23; 22, 23) are of Galilean type.

7. Scanning system (1) according to any one of claims 1 to 5, wherein the first and the second objective optics (21, 22) have a positive dioptric power; and wherein the image optics (23) has a positive dioptric power, such that the first and the second beam expander (21, 23; 22, 23) are of Keplerian type.

8. Scanning system (1) according to any one of the preceding claims, wherein the first objective optics (21) is movable along a respective optical axis (01) and / or the second objective optics (22) is movable along a respective optical axis (02) .

9. Scanning system (1) according to any one of the preceding claims, wherein the deflection assembly (3) comprises a pair of galvanometric mirrors (31, 32) configured to rotate about respective axes perpendicular to each other.

10. Processing system comprising:- a scanning system (1) according to any one of the preceding claims; - a first source (SI) configured to emit the first beam(Bl) with a first wavelength (Xi) ; and- a second source (S2) configured to emit the secondbeam (B2) with a second wavelength (X2) different from the first wavelength (Xi) ; and wherein the combination assembly (5) comprises a dichroic mirror (5) configured to transmit the first wavelength (Xi) and to reflect the second wavelength (X2) .

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