LASER PROCESSING HEAD HAVING A DIAPHRAGM TO INCREASE SCAN FIELD OF THE LASER BEAM

Abstract

A laser processing head is presented. The laser processing head includes a laser entry module for introducing a laser beam; a collimating module for collimating the laser beam; a scanning module for deflecting the laser beam; a focusing module for focusing the laser beam; and at least one diaphragm for increasing a scan field of the laser beam. The diaphragm comprises a diaphragm body and an opening, and is configured to limit a cross-sectional area of the laser beam by the diaphragm body. The at least one diaphragm is positioned optically downstream of the laser entry module and optically upstream of the focusing module. A laser processing system including the laser processing head is also presented. Furthermore, a method for increasing a scan field of the laser beam is also provided.

Claims

1. A laser processing head, comprising: a laser entry module for introducing a laser beam; a collimating module configured to collimate the laser beam; a scanning module configured to deflect the laser beam; and a focusing module configured to focus the laser beam; and at least one diaphragm for increasing a scan field of the laser beam; wherein the at least one diaphragm comprises a diaphragm body and an opening, and is configured to limit a cross-sectional area of the laser beam by the diaphragm body; and wherein the at least one diaphragm is positioned between the laser entry module and the focusing module.

2. The laser processing head according to claim 1, wherein: the at least one diaphragm is positioned such that an entire cross-sectional area of the laser beam having passed through the opening of the diaphragm is incident on an optical surface of an optical element; and the optical element is comprised in at least one of the collimating module, the scanning module and the focusing module.

3. The laser processing head according to claim 1, wherein the diaphragm body is arranged to obstruct an entire edge of the laser beam or to obstruct only a part of an entire edge of the laser beam.

4. The laser processing head according to claim 1, wherein the opening of the at least one diaphragm is smaller than an aperture of the focusing module.

5. The laser processing head according to claim 1, wherein the at least one diaphragm includes at least one of: a first diaphragm positioned between the laser entry module and the collimating module (44), and configured to limit the cross-sectional area of the laser beam propagating from the laser entry module (40) to the collimating module; a second diaphragm positioned between the collimating module and the scanning module, and configured to limit the cross-sectional area of the laser beam propagating from the collimating module to the scanning module; and a third diaphragm positioned between the scanning module and the focusing module, and configured to limit the cross-sectional area of the laser beam propagating from the scanning module to the focusing module.

6. The laser processing head according to claim 1, wherein the at least one diaphragm is configured such that the laser beam passing through the at least one diaphragm has a width less than 95% of a width of the laser beam received at the at least one diaphragm.

7. The laser processing head according to claim 1, wherein the at least one diaphragm is configured to adjustably limit a cross-sectional area of the laser beam passing therethrough.

8. The laser processing head according to claim 7, wherein the at least one diaphragm is configured to adjust a cross-sectional area of the opening to adjustably limit the cross-sectional area of the laser beam passing therethrough.

9. The laser processing head according to claim 7, wherein the at least one diaphragm is configured to move along an optical axis of the at least one diaphragm and/or in a plane perpendicular to the optical axis of the at least one diaphragm to adjustably limit the cross-sectional area of the laser beam passing therethrough.

10. The laser processing head according to claim 1, wherein: the diaphragm body comprises a coolant-based cooling mechanism to remove heat from the diaphragm body; and/or the diaphragm body comprises a surface coating configured to increase absorption of a portion of the laser beam hitting the diaphragm body; and/or the diaphragm body comprises a beam trap configured to trap, by repeated total internal reflections, a portion of the laser beam hitting the diaphragm body; and/or the diaphragm body comprises a reflector and an absorbing unit, and the reflector is arranged to reflect a portion of the laser beam hitting the diaphragm body towards the absorbing unit for absorbing the reflected portion of the laser beam.

11. The laser processing head according to claim 1, further comprising a sensor module comprising one or more sensors configured to sense a laser power of a portion of the laser beam having passed through the opening of the at least one diaphragm and/or to sense a laser power absorbed by the diaphragm body.

12. A laser processing system, comprising: The laser processing head according to claim 1; and a laser source module configured to generate the laser beam.

13. The laser processing system according to claim 12, wherein the laser source module comprises at least one of: a single-mode laser source, a multi-mode laser source, or a ring-mode laser source.

14. The laser processing system according to claim 12, wherein the laser source module comprises at least one of: a disk laser, a fiber laser, a fiber disk laser, a fiber laser with ring-mode, a disk laser with ring-mode, a diode laser, a single-mode fiber laser or a multi-mode fiber laser.

15. The laser processing system according to claim 12, wherein the laser source module is configured to generate a laser beam having a power of at least 200 W, or a power of at least 6 kW, or a power of at least 8 kW, or a power of at least 10 kW.

16. The laser processing system according to claim 12, further comprising a processor configured: to control the laser source module to adjust a laser power of the laser beam according to a sensed laser power of a portion of the laser beam passed through the opening (102) of the at least one diaphragm and/or according to a sensed laser power absorbed by the diaphragm body and/or according to a scan position of the laser beam deflected by the scanning module; and/or to control the at least one diaphragm to adjust the cross-sectional area of the laser beam passing through the at least one diaphragm according to a scan position of the laser beam deflected by the scanning module.

17. A method for controlling a laser processing head, the method comprising: introducing a laser beam at a laser entry module of the laser processing head; collimating the laser beam by a collimating module of the laser processing head; deflecting the laser beam by a scanning module of the laser processing head; and focusing the laser beam by a focusing module of the laser processing head; passing the laser beam through a diaphragm of the laser processing head such that a scan field of the laser beam is increased by limiting a cross-sectional area of the laser beam by the diaphragm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Any references to ‘radial’, ‘radially’, ‘circumferential’, ‘circumferentially’ and like phrases is to be understood with reference to a central axis of the component being referred to, unless otherwise stated.

[0063] The above mentioned attributes and other features and advantages of the present technique and the manner of attaining them will become more apparent and the present technique itself will be better understood by reference to the following description of embodiments of the present technique taken in conjunction with the accompanying drawings, wherein:

[0064] FIG. 1 schematically depicts a simplified exemplary embodiment of a laser processing system having a laser processing head of the present technique in which at least one diaphragm of the present technique is incorporated;

[0065] FIGS. 2A and 2B schematically depict functioning of an exemplary embodiment of the at least one diaphragm;

[0066] FIGS. 3A, 3B and 3C schematically depict increasing of scan field of the laser beam by the at least one diaphragm in comparison to laser beam projected without the at least one diaphragm;

[0067] FIG. 4 schematically depicts an exemplary embodiment wherein the diaphragm body obstructs only a part of an entire edge of the laser beam;

[0068] FIG. 5 schematically depicts an exemplary embodiment wherein the at least one diaphragm adjusts a cross-sectional area of the opening of the diaphragm to adjustably limit the cross-sectional area of the laser beam passing therethrough;

[0069] FIG. 6 schematically depicts an exemplary embodiment wherein the at least one diaphragm is moveable parallel to an optical axis of the diaphragm to adjustably limit the cross-sectional area of the laser beam passing therethrough;

[0070] FIG. 7 schematically depicts an exemplary embodiment wherein the at least one diaphragm is moveable in a plane perpendicular to an optical axis of the diaphragm to adjustably limit the cross-sectional area of the laser beam passing therethrough;

[0071] FIG. 8 schematically depicts an exemplary embodiment of the at least one diaphragm having a plurality of diaphragms to successively limit the cross-sectional area of the laser beam passing therethrough;

[0072] FIG. 9 schematically depicts an exemplary embodiment of the at least one diaphragm having a coolant-based cooling mechanism;

[0073] FIG. 10A schematically depicts an exemplary embodiment of the at least one diaphragm;

[0074] FIG. 10B schematically depicts an exemplary embodiment of the at least one diaphragm having a surface coating;

[0075] FIG. 11 schematically depicts an exemplary embodiment of the at least one diaphragm having a beam trap; and

[0076] FIG. 12 schematically depicts an exemplary embodiment of the at least one diaphragm having a reflector and an absorbing unit; in accordance with aspects of the present technique.

DETAILED DESCRIPTION OF THE INVENTION

[0077] Hereinafter, above-mentioned and other features of the present technique are described in detail. Various embodiments are described with reference to the drawing, wherein like reference numerals are used to refer to like elements throughout. In the following description, for purpose of explanation, numerous specific details are set forth in order to provide a thorough understanding of one or more embodiments. It may be noted that the illustrated embodiments are intended to explain, and not to limit the invention. It may be evident that such embodiments may be practiced without these specific details.

[0078] FIG. 1 depicts a laser processing system 2 having a laser processing head 1, such as a laser cutting head or a laser welding head, in which at least one diaphragm 100 according to the present technique is incorporated.

[0079] The laser processing system 2 may be any system which is used to transmit or irradiate a laser beam onto a target surface or a workpiece W. The laser processing system 2 may be one of, but not limited to, a laser cutting system, a laser engraving system, a laser ablation system, a laser drilling system, a laser beam machining system, a laser beam welding system, a laser hybrid welding system, a laser soldering system, an additive manufacturing system using laser such as a laser printing system, a laser cladding system, and so on and so forth.

[0080] The laser processing system 2 may include a laser beam generation source or laser source module 42, for generating a laser beam 9, and a laser processing head 1. The laser processing system may optionally include a processor 48.

[0081] The laser source module 42 may comprise a single-mode laser source or a multi-mode laser source. The laser source module 42 may be configured to generate a laser beam having a power of several hundreds of Watt, or a multi-kilowatt laser beam, e.g. of 2 kW or greater, for example 6 kW and greater or 8 kW and greater.

[0082] The laser processing head 1 may include a housing within which components of the laser processing head 1, e.g. optical elements for guiding the laser beam 9, may be disposed.

[0083] The laser processing head 1 includes a laser entry module 40 for introducing the laser beam 9, a collimating module 44 for collimating the laser beam 9, a scanning module 46 for scanning or deflecting the laser beam 9, and a focusing module 50 for focusing the laser beam 9 onto a work piece W.

[0084] The laser beam 9 may be fed to the laser processing head 1 via the laser entry module 40. The laser beam 9 is directed from the laser entry module 40 towards the focusing module 50, and thus defining an overall or general direction of transmission of the laser beam 9. The position or optical position of the different components relative to each other may be understood accordingly, for example, a location or position of the laser entry module 40 may be understood as an optically upstream location or position, whereas a location or position of the focusing module 50 may be understood as an optically downstream location or position. A direction generally extending from the laser entry module 40 towards the focusing module 50 may be understood as optically downstream, whereas a direction generally extending from the focusing module 50 towards the laser entry module 40 may be understood as optically upstream. All the directions may be understood along a direction of propagation or travel or transmission of the laser beam from the laser entry module 40 towards the focusing module 50. It may be noted that in the embodiment of FIG. 1 the laser entry module 40, the collimating module 44, the scanning module 46 and the focusing module 50 are linearly arranged, i.e. along a line. However, the depicted embodiment of FIG. 1 is only for exemplary purpose, and the present technique is not limited to the linear arrangement of the modules 40, 44, 46, 50. In other embodiments (not shown), the modules 40, 44, 46, 50 may be arranged differently, for example the laser entry module 40 and the collimating module 44 may be arranged normally or at an angle to the scanning module 46 and the focusing module 50.

[0085] The laser source module 42 may be coupled to the laser entry module 40, for example by optical fibers. The laser beam 9 generated by the laser source module 42 may be fed or introduced or provided to the laser processing head 1 at or via the laser entry module 40. The laser entry module 40 may be for example be exit ends of the optical fibers (not shown).

[0086] The laser beam 9 emerging out of the laser entry module 40 is directed towards the collimating module 44. The collimating module 44 may comprise at least one collimating optical element, e.g. one or more collimating lenses. The laser beam 9 is collimated by the collimating module 44. The collimated laser beam 9 may then be directed towards the scanning module 46.

[0087] The scanning module 46 may deflect the laser beam 9 in one-dimension or in two-dimensions. The scanning module 46 may comprise at least one scanning optical element, e.g. one or more scanning mirrors.

[0088] In order to position the laser beam 9 in two dimensions, either a one mirror arrangement is used in which the mirror is rotated along two axes e.g. two orthogonal axis or X-axis and Y-axis, or a two mirror arrangement is used that has two closely spaced mirrors—one for each orthogonal axis to reflect the laser beam along the corresponding axis. Each of the two mirrors may be driven by a galvanometer or by other actuation means such as an electric motor. For example, the scanning module may be a galvanometer scanner i.e. the scanning module 46 may have two galvanometers, each having a corresponding reflector such as a mirror to deflect the laser beam 9.

[0089] The laser beam 9 deflected or positioned or steered by the scanning module 46 is directed towards the focusing module 50. The laser beam 9 is focused by the focusing module onto the workpiece W.

[0090] The focusing module 50 may comprise at least one focusing optical element, e.g. one or more focusing lenses. The focusing module 40 may comprise a F-Theta lens. In other words, the focusing optical element may be a F-Theta lens.

[0091] The laser beam 9 may exit the laser processing head 1 through or via an exit opening or nozzle 58. The nozzle 58 may be located optically downstream of the focusing module 50.

[0092] The laser processing head 1 further comprises at least one diaphragm 100 configured to limit a diameter or cross-sectional area of the laser beam 9 passing therethrough in order to increase a scan field of the laser beam 9. The structure and function of the diaphragm 100 has been explained later with reference to FIGS. 2A and 2B, and the increasing of scan field has been explained later with reference to FIGS. 3A, 3B and 3C.

[0093] As shown in FIG. 1, the at least one diaphragm 100 may include a first diaphragm 10 positioned between the laser entry module 40 and the collimating module 44. The first diaphragm 10 may limit the cross-sectional area of the laser beam 9 transmitted from the laser entry module 40 towards the collimating module 44. The position or location between the laser entry module 40 and the collimating module 44 may be referred to as a first position.

[0094] The at least one diaphragm 100 may include a second diaphragm 20 positioned between the collimating module 44 and the scanning module 46. The second diaphragm 20 may limit the cross-sectional area of the laser beam 9 transmitted from the collimating module 44 towards the scanning module 46. The position or location between the collimating module 44 and the scanning module 46 may be referred to as a second position. Generally, at this position, all beams in the laser processing head are coaxial. For instance, optical beams of coaxial illumination systems or of distance measuring systems, such as optical coherence tomography (OCT), conoscope, intensity-based measuring systems, etc., may be combined with the laser beam by a beam splitter. Thus, the second diaphragm 20 may prevent too high intensity of these optical beams being incident on the following optical elements and reduce a scattering of light for improving a signal to noise ratio or a contrast.

[0095] The at least one diaphragm 100 may include a third diaphragm 30 positioned between the scanning module 46 and the focusing module 50. The third diaphragm 30 may limit the cross-sectional area of the laser beam 9 transmitted from the scanning module 46 towards the focusing module 50. The position or location between the scanning module 46 and the focusing module 50 may be referred to as a third position.

[0096] The at least one diaphragm 100 may include only one of, only two of or all of the first diaphragm 10, the second diaphragm 20 and the third diaphragm 30. For example the at least one diaphragm 100 may include only the first diaphragm 10, or only the second diaphragm 20, or only the third diaphragm 30, or only the first diaphragm 10 and the second diaphragm 20, or only the first diaphragm 10 and the third diaphragm 30, or only the second diaphragm 20 and the third diaphragm 30, or all of the first diaphragm 10, the second diaphragm 20 and the third diaphragm 30.

[0097] In general, the at least diaphragm 100 is positioned optically downstream of the laser entry module 40 and optically upstream of the focusing module 50.

[0098] Hereinafter, structure and function of an exemplary embodiment of the at least one diaphragm 100 is described with reference to FIGS. 2A and 2B, FIGS. 3A to 3C and FIG. 10A.

[0099] As shown in FIG. 10A, the first diaphragm 10 comprises a diaphragm body 14 and an opening 12. The second diaphragm 20 comprises a diaphragm body 24 and an opening 22. The third diaphragm 30 comprises a diaphragm body 34 and an opening 32. The first, second and/or the third diaphragm 10, 20, 30 have been represented as the diaphragm 100 hereinafter. The description provided with respect to the diaphragm 100 is also applicable to each of the first, the second and the third diaphragms 10, 20, 30. The diaphragm 100 comprises a diaphragm body 104 and an opening 102. The diaphragm 100 may have an annular shape, wherein the diaphragm body 104 defines the opening 102. The diaphragm body 104 may have a planar shape for example a disk shape. Generally, the at least one diaphragm 100 is positioned optically downstream of the laser entry module 40 and optically upstream of the focusing module 50, in other words the at least one diaphragm 100 is positioned optically between the laser entry module 40 and the focusing module 50.

[0100] As previously mentioned, the focusing module 50 may comprise at least one focusing optical element, e.g. one or more focusing lenses. Similarly, the collimating module 44 may comprise at least one collimating optical element, e.g. one or more collimating lenses. Also, the scanning module may comprise at least one scanning optical element, e.g. one or more scanning mirrors. The focusing optical element and/or the collimating optical element and/or the scanning optical element may generally be referred to as the optical element 52.

[0101] FIG. 2A shows functioning of the diaphragm 100, for example the diaphragm 100 may be the third diaphragm 30, positioned between the scanning module 46 and the focusing module 50.

[0102] Generally, the diaphragm 100 is positioned upstream of the optical element 52, e.g. upstream of a F-theta lens functioning as the focusing optical element 52. Arrows 9x depict a direction of propagation or travel of the laser beam 9. The diaphragm 100 and the optical element 52 may be disposed to be spaced apart from each other, i.e. may not be in contact with each other.

[0103] The diaphragm 100 limits a cross-sectional area 9c of the laser beam 9 by the diaphragm body 104. In other words, the diaphragm 100 is dimensioned and positioned to allow a first part or portion 91 of the laser beam 9 to pass through the opening 102, while obstructing a second part or portion 92 of the laser beam 9 by the diaphragm body 104. The obstructing may be performed by physically blocking the beam, and for this purpose at least a part of the diaphragm body 104 may be disposed in the path of travel or propagation path of the laser beam 9. In other words, the cross-sectional area 9c of the laser beam 9 is sectioned or divided or cleaved by the diaphragm 100 into a cross-sectional area 91c of the laser beam 9 thereby defining the first portion 91 of the laser beam 9 which is allowed to pass towards the downstream side of the diaphragm 100 through the opening 102, and into a cross-sectional area 92c of the laser beam 9 thereby defining the second portion 92 of the laser beam 9 which is obstructed or stopped at the upstream side of the diaphragm 100 by the diaphragm body 104. In short, a part of the laser beam 9, i.e. the second portion 92, of the laser beam 9 is stopped by the diaphragm body 104 from being propagated or transmitted towards the optical element 52.

[0104] Simply put, as shown in FIG. 2A, the diaphragm 100 limits a cross-sectional area of the laser beam 9. To explain further, a cross-sectional area 91c of the laser beam 9 having passed through the diaphragm 100, i.e. the cross-sectional area 91c of the first portion 91 of the laser beam 9, is smaller than a cross-sectional area 9c of the laser beam 9 upstream of the diaphragm 100 i.e. the laser beam 9 when received at the diaphragm 100.

[0105] In other words, as shown in FIG. 2A, the diaphragm 100 limits a diameter of the laser beam 9. To explain further, a diameter 91d of the laser beam 9 having passed through the diaphragm 100, i.e. the diameter 91d of the first portion 91 of the laser beam 9, is smaller than a diameter 9d of the laser beam 9 upstream of the diaphragm 100 i.e. the laser beam 9 when received at the diaphragm 100.

[0106] In other words, as shown in FIG. 2A, the diaphragm 100 limits a periphery 9p of the laser beam 9. To explain further, a periphery or edge 91p of the laser beam 9 having passed through the diaphragm 100, i.e. the periphery 91p of the first portion 91 of the laser beam 9, is smaller than the periphery 9p of the laser beam 9 upstream of the diaphragm 100 i.e. the laser beam 9 when received at the diaphragm 100.

[0107] It may be noted that although FIG. 2A, and some other FIGs show an optical axis 100x of the diaphragm 100 to be coincident or coaxial with an optical axis 52x of the optical element 52, the diaphragm 100 may be arranged such that the optical axis 100x of the diaphragm 100 may not be coincident with the optical axis 52x of the optical element 52, for example the optical axis 100x of the diaphragm 100 may be disposed parallel to and spaced apart from the optical axis 52x of the optical element 52 e.g. as shown in FIG. 3C.

[0108] The diaphragm 100 may be disposed in the path of the laser beam 9 propagating towards the optical element 52, for example propagating towards the focusing module 50 after being deflected by the scanning module 46.

[0109] The laser processing head 1 may include a diaphragm positioning mechanism (not shown) configured to dispose and remove, i.e. reversibly dispose and remove, the diaphragm 100 in and from the path of the laser beam 9 propagating towards the optical element 52. By removing or disposing the diaphragm 100 in the path of the laser beam 9, beam characteristics such as power density distribution and beam size i.e. width or cross-sectional area of the laser beam 9, may be changed.

[0110] The laser processing head 1 may include a diaphragm aligning mechanism (not shown) configured to align, i.e. to move the diaphragm 100 for aligning or orienting the diaphragm 100 with respect to the laser beam 9. In other words, the laser beam 9 may be incident onto a first location on the optical surface 54 of the optical element 52 along with the diaphragm 100 disposed in the beam path, and then the laser beam 9 may be repositioned to be incident onto a second location on the optical surface 54 of the optical element 52. When the laser beam 9 is repositioned, the diaphragm aligning mechanism aligns or repositions the diaphragm 100 accordingly or correspondingly, such that the diaphragm 100 is redisposed or continues to remain disposed in the beam path of the laser beam 9 propagating towards the optical element 52. The movement of the diaphragm 100 for repositioning of the diaphragm 100 may be performed simultaneously along with the scanning movement of the laser beam 9 i.e. while the laser beam 9 is being repositioned by the scanning module 46.

[0111] The diaphragm aligning mechanism may be configured to move the diaphragm parallel to or along the optical axis 100x of the diaphragm 100 and/or parallel to or along the optical axis 52x of the optical element 52 and/or in a plane perpendicular to the optical axis 100x of the diaphragm 100 and/or perpendicular to the optical axis 52x of the optical element 52—to variably or adjustably limit the cross-sectional area 91c of the laser beam 9 passing therethrough. The variable or adjustable limiting of the cross-sectional area 9c of the laser beam 9 has been explained later with respect to FIGS. 6 and 7.

[0112] FIG. 2B shows the laser beam 9 and parts of the laser beam 9 i.e. the first portion 91 that is allowed to pass through the opening 102 and the second portion 92 that is obstructed by the diaphragm body 104, and their corresponding intensity or power distributions as shown by the curve 80. The curve 80 shows intensity or power distribution of the laser beam 9 with respect to a radius or radial distance from a central axis of the laser beam 9. Axis 81 depicts the radial distance or beam waist ‘ω’ whereas the axis 82 depicts the intensity ‘I’. Lines I, II, III and IV have been included to depict the correspondence of sections of the curve 80 or of area under the curve 80 with sections or portions, e.g. the first portion 91 and the second portion 92, of the laser beam 9.

[0113] The curve 80 represents a typical laser beam 9 having a Gaussian-shaped intensity distribution or an intensity distribution similar to a Gaussian-shaped intensity distribution. I.sub.0 i.e. the maximum value provided on the axis 82 describes the intensity, and correspondingly the power, at its maximum. Radial distance Wo, i.e. distance from the center axis of the laser beam 9 depicts the distance or radius, at which the intensity of the beam drops to 1/e.sup.2 of the maximum. The areas of the beam 9 farther away from the center axis of the beam 9 experience a further drop in intensity, i.e. lesser than 1/e.sup.2, as can be seen from FIG. 2B.

[0114] As can be seen from FIG. 2B, the at least one diaphragm 100 allows the portion of the beam 9 with higher intensity or higher power density distribution to pass through such as portion of the beam between lines II and III, and obstructs one or more peripheral portions of the beam 9 such as the portion of the beam between lines I and II and portion of the beam between lines III and IV which represent lower intensity or lower power density distribution. Simply put the portion of the beam 9 with relatively lower intensity, such as the second portion 92, are stopped by the diaphragm 100 whereas the portion of the beam 9 with relatively higher intensity, such as the first portion 91, are allowed by the diaphragm 100 to pass therethrough. More precisely, the portion of the beam 9 with relatively lower intensity to radial distance ratio of the beam 9, such as the second portion 92, are stopped by the diaphragm 100 whereas the portion of the beam 9 with relatively higher intensity to radial distance ratio of the beam 9, such as the first portion 91, are allowed by the diaphragm 100 to pass therethrough. In short, the first portion 91 of the laser beam 9 has a greater intensity to cross-sectional area ratio, as compared to intensity to cross-sectional area ratio of the second portion 92. Simply put, the power density distribution of the first portion 91 of the laser beam 9 is greater than or higher than the power density distribution of the second portion 92 of the laser beam 9.

[0115] As explained above, ω.sub.0 is radial distance from the central axis of the laser beam 9 at which the intensity has dropped to 1/e.sup.2 i.e. approx. 13.5%. The energy beyond or outside of the radius ω.sub.0, for example in the region of the laser beam 9 between the lines I and II and between the lines III and IV, may be high enough to heat up and destroy structures but may be too low or little to be used for processing. Thus, the diaphragm 100 is such that the first portion 91 of the laser beam 9 extends from the central axis of the laser beam 9 up to a radial distance ω.sub.0, and the second portion 92 of the laser beam 9 extends beyond or radially outward of radial distance ω.sub.0.

[0116] In other words, the diaphragm 100 may be configured, i.e. positioned and/or oriented and/or dimensioned such that the laser beam 9 passing through the diaphragm has 1/e.sup.2 width or radius of the laser beam 9 received at the diaphragm 100. In other words, the diameter 91d or radius of the first portion 91 of the laser beam 9 is 1/e.sup.2 of the diameter 9d or radius of the laser beam 9 upstream of the diaphragm 100.

[0117] The at least one diaphragm 100 may be configured such that an intensity of the laser beam exiting optically downstream therefrom is between 75% and 90%, preferably between 85% and 87%, and more preferably about 86.5% of a total intensity of the laser beam received at the at least one diaphragm.

[0118] When the at least one diaphragm 100 includes at least two of the first, the second and the third diaphragm 10, 20, 30, the cross-sectional areas of the openings of the first diaphragm 10, the second diaphragm 20 and the third diaphragm 30 may be such that an intensity of the laser beam 9 exiting the diaphragm 100 positioned farthest downstream is between 75% and 90%, preferably between 85% and 87%, and more preferably about 86.5% of a total intensity of the laser beam 9 received at the diaphragm 100 positioned farthest upstream.

[0119] For comparative understanding, FIG. 3A shows a laser beam 9 having a central axis 99x and whose cross-sectional area has not been limited by the diaphragm 100. As can be seen from FIG. 3A, a part of the periphery 9p of the laser beam 9 falls at and beyond an edge of the optical surface 54, and may therefore undesirably deposit energy into the edge or into structures or components (not shown) adjoining the optical element 52, such as a lens holder, which may consequently cause adverse effects such as heating of the optical element 52 and/or of the adjoining structures or components, such as of the lens holder. Thus, as shown in FIG. 3B, conventionally a scan field S is defined which is a maximum recommended navigable area of the central axis 99x of the beam 9 so as to avoid the periphery 9p of the laser beam 9 to fall beyond the edge of the optical surface 54, and to avoid related adverse effects, such as heating, of the optical element and/or of the adjoining structures or components. Thus, a limited size of the scan field S is realized in conventional laser processing heads.

[0120] However, in the laser processing head 1 of the present technique as shown in FIG. 3C, by using the diaphragm 100, the first portion 91 of the laser beam 9 having the greater intensity or power to cross-sectional area ratio is emitted out from the laser processing head 1 for laser processing whereas the second portion 92 having lower intensity or power to cross-sectional area ratio is obstructed by the diaphragm 100. In short, although the beam diameter or the cross-sectional area of the laser beam 9 provided onto the workpiece via the optical element 52 is lesser in FIG. 3C compared to that in FIGS. 3A and 3B, the intensity is still sufficient for laser processing. Since the beam diameter is reduced, the size or area of the scan field S of the beam 9 may be increased. Simply put, the central axis 99x of the beam 9 can be positioned by the scanning module 46 to be closer to the edges of the optical surface 54 without the periphery 9p of the laser beam 9 extending beyond the edge of the optical surface 54.

[0121] As shown in FIG. 2A, the at least one diaphragm 100 may be configured, i.e. dimensioned or positioned and/or oriented, for example with respect to the focusing module 50 or the collimating module 44 or the scanning module 46, such that an entire cross-sectional area 91c of the laser beam 9, or the periphery 91p of the entire cross-sectional area 91c of the laser beam 9 having passed through the opening 102 of the diaphragm 100, i.e. of the first portion 91 of the laser beam 9, is incident on or transmitted through the optical surface 54 of the optical element 52.

[0122] As shown in FIG. 2A, the diaphragm 100 may be configured, i.e. dimensioned or positioned and/or oriented, such that the entire edge or periphery 9p of the laser beam 9 is obstructed by the diaphragm body 104. Alternatively, as shown in FIG. 4, the diaphragm 100 may be configured, i.e. dimensioned or positioned and/or oriented, such that only a part of the entire edge or the periphery 9p of the laser beam 9 is obstructed by the diaphragm body 104.

[0123] It may be noted that the opening 102 of the diaphragm 100 may be smaller than an aperture of the optical element 52 such as than an aperture of the F-theta lens. However, the function of the diaphragm 100 as explained with reference to FIG. 2B may also be achieved by a diaphragm 100 in which the opening 102 may not be smaller than the aperture of the optical element 52, by positioning the diaphragm 100 in such a way that at least a part of the laser beam 9 is obstructed by the diaphragm body 104.

[0124] It may further be noted that although the diaphragm 100 is depicted as one diaphragm 100 at one position, the at least one diaphragm 100 may include a plurality of diaphragms 100a, 100b as shown in FIG. 8, which may successively limit the cross-sectional area 9c of the laser beam 9 as shown in FIG. 8. The plurality of diaphragms 100a, 100b may include an upstream diaphragm 100a and a downstream diaphragm 100b, with respect to the optical element 52 and the direction 9x. An opening 102a of the upstream diaphragm 100a may be smaller than an opening 102b of the downstream diaphragm 100b. The plurality of diaphragms 100a, 100b may be moveable with respect to each other and/or relative to the optical element 52, in a direction parallel to or along the optical axis 100x of the diaphragm 100 and/or parallel to or along the optical axis 52x of the optical element 52 and/or in a plane perpendicular to the optical axis 100x of the diaphragm 100 and/or perpendicular to the optical axis 52x of the optical element 52—to variably or adjustably limit the cross-sectional area 9c of the laser beam 9 passing therethrough.

[0125] One or more of each of the first, the second and the third diaphragms 10, 20, 30 may include the upstream and the downstream diaphragms 100a, 100b, as explained hereinabove.

[0126] The at least one diaphragm 100 may be configured to adjustably or variably limit the cross-sectional area of the laser beam 9, i.e. to vary the cross-sectional area 91c of the first portion 91 of the laser beam 9, passing therethrough. FIG. 5 schematically depicts an exemplary embodiment wherein the at least one diaphragm 100 adjusts or varies the cross-sectional area 102c of the opening 102 of the diaphragm 100 and consequently the cross-sectional area 91c of the laser beam 9 passing therethrough is varied or adjusted. The diaphragm body 104 may be formed as a mechanical iris or mechanical shutter which may move in a radially to-and-fro direction to vary the cross-sectional area 102c or radius or diameter of the opening 102. Thus, the cross-sectional area 91c or the diameter 91d of the first portion 91 of the laser beam 9, passing therethrough may be varied. In other words, a proportion of the first portion 91 of the laser beam 9 and the second portion 92 of the laser beam 9 may be varied by radially increasing or decreasing the opening 102 of the diaphragm 100. More specifically, a proportion of the cross-sectional area 91c of the first portion 91 of the laser beam 9 and the cross-sectional area 92c of second portion 92 of the laser beam 9 may be varied by radially increasing or decreasing the opening 102 of the diaphragm 100. The diaphragm body 104 may be moved to radially increase or decrease the opening 102 of the diaphragm 100 by using an actuator such as a motor (not shown).

[0127] FIG. 6 schematically depicts an exemplary embodiment wherein the at least one diaphragm 100 is moveable parallel to or along an optical axis 100x of the diaphragm 100 to adjustably limit the cross-sectional area 91c of the laser beam 9 passing therethrough. As can be seen from FIG. 6, a distance D1, D2 between the diaphragm 100 and the optical surface 54 may be increased or decreased, for example be the diaphragm aligning mechanism (not shown), prevision mentioned. Thus, as shown in FIG. 6 the at least one diaphragm 100 may be configured to adjustably or variably limit the cross-sectional area of the laser beam 9, i.e. to vary the cross-sectional area 91c of the first portion 91 of the laser beam 9, passing therethrough. The diaphragm body 104 may move in an axially to-and-fro direction to vary the cross-sectional area 91c of the first portion 91 of the laser beam 9. Thus, the cross-sectional area 91c or the diameter 91d of the first portion 91 of the laser beam 9, passing therethrough may be varied. In other words, a proportion of the first portion 91 of the laser beam 9 and the second portion 92 of the laser beam 9 may be varied by axially increasing or decreasing the distance D1, D2 of the diaphragm 100 from the optical surface 54 or the optical element 52 or the focusing module 50 or the scanning module 46 or the collimating module 44. More specifically, a proportion of the cross-sectional area 91c of the first portion 91 of the laser beam 9 and the cross-sectional area 92c of second portion 92 of the laser beam 9 may be varied by axially increasing or decreasing the distance D1, D2 of the diaphragm 100 from the optical surface 54. The diaphragm body 104 may be moved axially using the diaphragm aligning mechanism which may use an actuator such as a motor (not shown).

[0128] FIG. 7 schematically depicts an exemplary embodiment wherein the at least one diaphragm 100 is moveable in a plane perpendicular to the optical axis 100x of the diaphragm 100—as can be seen from distance between the optical axis 100x of the diaphragm 100 and the optical axis 52x of the optical element 52 by a comparison of (a) and (b) depictions in FIG. 7—to adjustably limit the cross-sectional area 91c of the laser beam 9 passing therethrough. As can be seen from FIG. 7, a lateral or horizontal distance or radial distance between the optical axis 100x of the diaphragm 100 and the optical axis 52x the optical surface 54 may be increased or decreased, for example be the diaphragm aligning mechanism (not shown).

[0129] It may be noted that the diaphragm aligning mechanism may be configured to simultaneously move the diaphragm 100 along or parallel to the optical axis 100x of the diaphragm 100 and/or along or parallel to the optical axis 52x of the optical element 52 and/or in a plane perpendicular to the optical axis 100x of the diaphragm 100 and/or in a plane perpendicular to the optical axis 52x of the optical element 52—to variably or adjustably limit the cross-sectional area of the laser beam 9 passing therethrough.

[0130] Hereinafter, with reference to FIGS. 9-12 various exemplary embodiments of the diaphragm 100 are explained.

[0131] FIG. 9 schematically depicts an exemplary embodiment of the at least one diaphragm having a coolant-based cooling mechanism 70. Preferably, the diaphragm having a cooling mechanism may be stationary, i.e. not movable. In this case, the cooling mechanism can be designed rather simple as when compared to cooling mechanisms for moving elements. The coolant-based cooling mechanism 70 includes a coolant 71 that flows through a cooling channel or coolant flow channel 72 or coolant flow path 72. The coolant flow channel 72 may be in surface contact with at least a part of a surface of the diaphragm body 104. Preferably, the coolant flow channel 72 is disposed at a surface of the diaphragm body 104 facing optically downstream direction, in other words at a surface opposite to the surface at which the laser beam 9 is obstructed. The coolant 71 enters the coolant flow channel 72 via an inlet 72a of the coolant flow channel 72, flows through the coolant flow channel 72 and performs heat exchange or cooling of the diaphragm body 104 while flowing through the coolant flow channel 72, and exits the coolant flow channel 72 via an outlet 72b of the coolant flow channel 72. The coolant 71 may be water. The coolant-based cooling mechanism 70 removes heat from the diaphragm body 104, which the diaphragm body 104 may have acquired for example from the second portion 92 of the laser beam 90 obstructed by the diaphragm body 104.

[0132] FIG. 10B schematically depicts an exemplary embodiment of the at least one diaphragm 100 having a surface coating 73. The surface coating 73 may be applied to at least one surface of the diaphragm body 104. Preferably, the surface coating 73 may be disposed at a surface of the diaphragm body 104 facing optically upstream direction, in other words to the surface at which the laser beam 9 is obstructed or incident. The surface coating 73 functions to absorb the incident laser beam 9, i.e. the second portion 92 of the laser beam 9, and thus obviates undesired reflection or scattering of the laser power after impacting the diaphragm body 104.

[0133] FIG. 11 schematically depicts an exemplary embodiment of the at least one diaphragm 100 having a beam trap 74. The beam trap 74 may be formed within the diaphragm body 104. Preferably, the beam trap 74 may be disposed at a surface of the diaphragm body 104 facing optically upstream direction, in other words at the surface at which the laser beam 9 is obstructed. The beam trap 74 functions to absorb the incident laser beam 9 by subjecting the incident laser beam 9, i.e. at least a part of the second portion 92 of the laser beam 9, to repeated total internal reflections, and thus obviates undesired reflection or scattering of the laser power after impacting the diaphragm body 104. It may be noted that depiction of FIG. 11 shows an exploded view of the diaphragm 100 for ease of understanding of the total internal reflections.

[0134] FIG. 12 schematically depicts an exemplary embodiment of the at least one diaphragm 100 having a reflector 76 and an absorbing unit 78. The reflector 76, which may be a mirror, may be formed on or at a surface of the diaphragm body 104, for example in form of a reflective coating. Thus, the reflector 76 may have a shape of a circular mirror with a hole in the center. Preferably, the reflector 76 may be disposed at a surface of the diaphragm body 104 facing optically upstream direction, in other words to the surface at which the laser beam 9 is obstructed or incident. The reflector 76 functions to reflect the incident laser beam 9, i.e. at least a part of the second portion 92 of the laser beam 9, towards the absorbing unit 78. The absorbing unit 78 may be disposed to receive the reflected part of the laser beam 9 and functions to absorb the incident laser beam 9 and thus obviates undesired reflection or scattering of the laser power after impacting the diaphragm body 104. The absorbing unit 78 may be actively cooled for example by using a coolant-based cooling mechanism, similar to the above-described coolant-based cooling mechanism 70. Thus, the position at which the laser power is absorbed can be distant from the obstructing surface, i.e. from the reflector.

[0135] As shown in FIG. 1, the laser processing head 1 may include a sensor module 60 comprising one or more sensors 62 configured to sense a laser power of a portion, e.g. the first portion 91, of the laser beam 9 having passed through the opening 102 of the diaphragm 100 and/or to sense a laser power absorbed by the diaphragm body 104. The laser sensor module 60 may comprise one or more sensors 61 configured to sense a laser power of the laser beam 9 upstream of the diaphragm 100. The sensor 62 configured to sense the laser power of the portion of the laser beam 9, i.e. the first portion 91, passed through the opening 102 of the diaphragm 100, may be positioned or located at the nozzle 58, particularly at the opening of the nozzle 58 of the laser processing head 1, and more particularly outside or downstream of the opening of the nozzle 58 of the laser processing head 1.

[0136] As previously mentioned with reference to FIG. 9, the diaphragm body 104 may have the coolant-based cooling mechanism 70. The sensor module 60 may include a temperature sensor 63, e.g. a first temperature sensor 63, disposed at the inlet 72a of the coolant flow channel 72 to measure or determine a temperature of the coolant 71 entering the coolant flow channel 72. The sensor module 60 may include a temperature sensor 64, e.g. a second temperature sensor 64, disposed at the outlet 72b of the coolant flow channel 72 to measure or determine a temperature of the coolant 71 exiting the coolant flow channel 72.

[0137] One or more of the sensors 61, 62 of the sensor module 60 may communicate with a processor 48 of the laser processing head 1 or the system 2.

[0138] One or more of the sensors 63, 64 of the sensor module 60 may communicate with the processor 48 of the laser processing head 1. From a difference in sensed temperatures by the temperature sensors 63, 64, the processor 48 may determine a laser power of a portion, e.g. the first portion 91, of the laser beam 9 passed through the opening 102 of the diaphragm 100 and/or to sense a laser power absorbed by the diaphragm body 104.

[0139] The processor 48 may be configured to control the laser source module 42 to adjust a laser power of the laser beam 9 generated by the laser source module 42 according to a sensed or determined laser power of a portion, i.e. the first portion 91, of the laser beam 9 passed through the opening 102 of the diaphragm 100 and/or according to a sensed laser power absorbed by the diaphragm body 104.

[0140] The processor 48 may be configured to control the diaphragm 100 to adjust or vary the cross-sectional area 91c of the laser beam 9 passing through the diaphragm 100, for example according to a sensed or determined laser power of a portion, i.e. the first portion 91, of the laser beam 9 having passed through the opening 102 of the diaphragm 100 and/or according to a sensed laser power absorbed by the diaphragm body 104 and/or according to a scan position of the laser beam deflected by the scanning module.

[0141] The processor 48 may control the diaphragm body 104 or a corresponding actuator to vary or adjust the cross-sectional area 102c of the opening 102 of the at least one diaphragm 100 to variably or adjustably limit the cross-sectional area 91c of the laser beam 9 passing therethrough—as explained with reference to FIG. 5.

[0142] The processor 48 may control the diaphragm body 104 or the corresponding aligning mechanism or actuator to move the diaphragm 100 along or parallel to the optical axis 100x of the diaphragm 100 and/or along or parallel to the optical axis 52x of the optical element 52 and/or in a plane perpendicular to the optical axis 100x of the diaphragm 100 and/or in a plane perpendicular to the optical axis 52x of the optical element 52, e.g. according to a scan position of the laser beam deflected by the scanning module, to variably or adjustably limit the cross-sectional area of the laser beam passing therethrough—as explained with reference to FIGS. 6 and 7.

[0143] In a third aspect of the present technique, a method for increasing a scan field S of the laser beam 9 is presented. The method may be for the laser processing head 1 or for the laser processing system 2 as explained hereinabove with reference to FIGS. 1 to 12. In the method, a laser beam 9 is introduced at the laser entry module 40, then the laser beam 9 is collimated by the collimating module 44, then the laser beam 9 is deflected by the scanning module 46, and then the laser beam 9 is focused, for example on a workpiece W, by the focusing module 50. In the method, the cross-sectional area 9c of the laser beam 9 is limited by the diaphragm body 104 by passing the laser beam 9 through the diaphragm 100 as explained hereinabove with reference to FIGS. 1 to 12.

[0144] In the present technique, when a multi-mode laser is used, by inserted the diaphragm 100 between the collimating module 44 and the laser entry module 40, some or all higher transverse modes may be cut off by the diaphragm body 104. The remaining laser beam can be focused to a smaller focus diameter, since the beam parameter product remains constant. The inserted diaphragm 100 may act like an optical fiber with a smaller fiber diameter.

[0145] Thus, it is possible to adjust the beam quality of the laser by inserting or moving an diaphragm 100 along the optical axis between the collimating module and the laser entry module. Thus, a single laser processing head or system can be used to perform both joining tasks that require high laser power but are less demanding in terms of the lateral extension of the joint, and tasks that require a very small focus diameter in order to perform the most precise processing possible. Switching or changing the beam quality and thus the focus size can be done during processing. Also, laser beam sources with a relatively low spatial beam quality, such as diode lasers or multi-mode fiber lasers, may be used with a small and compact scanning module, while maintaining a good processing quality.

[0146] In the present technique, the diaphragm 100 may also be understood as an aperture or stop.

[0147] While the present technique has been described in detail with reference to certain embodiments, it should be appreciated that the present technique is not limited to those precise embodiments. Rather, in view of the present disclosure which describes exemplary modes for practicing the invention, many modifications and variations would present themselves, to those skilled in the art without departing from the scope of the appended claims. The scope of the invention is, therefore, indicated by the following claims rather than by the foregoing description.