GB2629349A

GB2629349A - Apparatus and method for directing laser radiation onto a target, laser drilling apparatus and method

Info

Publication number: GB2629349A
Application number: GB2305964.5A
Authority: GB
Inventors: Milne David
Original assignee: M Solv Ltd
Current assignee: M Solv Ltd
Priority date: 2023-04-24
Filing date: 2023-04-24
Publication date: 2024-10-30
Also published as: GB202305964D0

Abstract

A laser beam may be dynamically varied using a changeable aperture and/or beam divergence; adjusting the cross-sectional intensity profile and altering the proportion of the beam removed by an aperture body 31. Laser 2 may produce a first beam 21, which can be dynamically varied by beam divergence unit 32, to create second beam 22. Second beam 22 can pass through a variable aperture body 31 (which can move closer/further from the laser 2; or increase/decrease aperture size like an iris/diaphragm) to change the beam intensity. The outer periphery of the beam may be removed, creating a near top hat intensity profile to promote sharper cutting edges; from a Gaussian profile (figure 2). Dynamic manipulation of the beam may involve adjusting lenses. The laser beam may be split into sub-beams in laser drilling/boring electrical vias in a substrate (figure 5). The spot shape may be adjusted.

Description

APPARATUS AND METHOD FOR DIRECTING LASER RADIATION ONTO A TARGET, LASER DRILLING APPARATUS AND METHOD The present disclosure relates to directing laser radiation onto a target, and particularly to performing laser drilling in the target.

Laser drilling in a target is widely known and particularly useful where small structures need to be formed quickly, with high accuracy and/or with high flexibility in terms of the positioning and/or form of manufactured features. The technique is commonly used, for example, to form holes for electrical vias, which may need to vary in size, shape and position. It can be challenging to provide an optimal balance between manufacturing throughput, flexibility and device complexity.

It is an object of the present disclosure to provide improved ways of directing laser radiation onto a substrate, particularly in the context of laser drilling.

According to an aspect of the invention, there is provided an apparatus for directing laser radiation onto a target, comprising: a laser configured to generate a first beam of radiation; a beam adjusting arrangement configured to adjust the first beam to provide a second beam, wherein the beam adjusting arrangement comprises an aperture body defining an aperture for transmitting the second beam, the aperture body being configured to remove a portion of the first beam to provide the second beam; and a downbeam optical system configured to direct the second beam, or a plurality of sub-beams derived from the second beam, onto the target, wherein the beam adjusting arrangement is configured to provide dynamic adjustment of a cross-sectional intensity profile at the target of the second beam, or of the plurality of sub-beams derived from the second beam, by dynamically varying: a proportion of the first beam that is removed by the aperture body; and/or a divergence of the second beam at the aperture body.

Configuring an apparatus to dynamically adjust a cross-sectional intensity profile in the way defined above enables rapid changes to be made to the profile using simple and/or widely available mechanisms (e.g., mechanisms used in computer numerical control (CNC) machines). The adjustment of the profile may include a change in size of the profile (e.g., making a beam spot on the target larger or smaller) and/or a change in shape of the profile (e.g., making the profile resemble a top hat function more or less closely, for example to transition between a quasi-top hat function, wherein the profile is close to a top-hat function, and a truncated Gaussian function, where the profile is further from a top-hat function and retains more of the Gaussian form of a laser output). Adjusting the profile by changing a proportion of the first beam that is removed by the aperture body can be implemented efficiently using techniques for driving and controlling accurate movement of components, such as have been developed in the context of CNC machines. As explained below, the adjustment can be performed for example by driving rapid controlled movement of the aperture body, of a divergence unit, and/or of one or more optical components of a divergence unit.

In an embodiment, the beam adjusting arrangement is configured to dynamically vary the proportion of the first beam that is removed by the aperture body by dynamically varying a cross-sectional size of the first beam at the aperture body. This approach provides efficient and flexible control of the shape of the intensity profile, for example allowing efficient and flexible switching between shapes that resemble a top hat function to different extents.

In an embodiment, the beam adjusting arrangement comprises an aperture body actuator configured to drive movement of the aperture body along a beam path of the first beam. In an embodiment, the beam adjusting arrangement is configured to vary the cross-sectional size of the first beam at the aperture body at least partially by driving movement of the aperture body using the aperture body actuator. Such movement of the aperture body can be implemented efficiently, for example using CNC technology, and allows rapid and reliable adjustment of the intensity profile at the target.

In an embodiment, the beam adjusting arrangement comprises a divergence unit configured to impart and/or adjust divergence in the first beam in a portion of a beam path of the first beam upbeam of the aperture body. The beam adjusting arrangement further comprises a divergence unit actuator configured to adjust a divergence contributed by the divergence unit. The divergence unit actuator provides a degree of freedom for controlling the intensity profile (size and/or shape) at the target that can be implemented simply and efficiently, for example using CNC technology.

According to an aspect of the invention, there is provided a laser drilling apparatus configured to remove material from a target by laser drilling. The laser drilling apparatus comprises an apparatus for directing laser radiation onto a target according to any embodiment of the disclosure.

According to an aspect of the invention, there is provided a method of directing laser radiation onto a target, the method comprising: using a laser to generate a first beam of radiation; using an aperture body to adjust the first beam to provide a second beam, the aperture body defining an aperture for transmitting the second beam and acting to remove a portion of the first beam to provide the second beam; and directing the second beam, or a plurality of sub-beams derived from the second beam, onto the target, wherein the method comprises dynamically adjusting a cross-sectional intensity profile at the target of the second beam, or of the plurality of sub-beams derived from the second beam, by dynamically varying: a proportion of the first beam that is removed by the aperture body; and/or a divergence of the second beam at the aperture body.

According to an aspect of the invention, there is provided a method of removing material from a target. The method comprises performing laser drilling by directing laser radiation onto the target using any method of the disclosure.

Embodiments of the disclosure will now be further described, merely by way of example, with reference to the accompanying drawings.

Figure 1 is an example of apparatus for directing laser radiation onto a target having an actuatable aperture body.

Figures 2(a)-(c) show example intensity profiles of a beam spot at a target surface.

Figure 3 is an example of apparatus for directing laser radiation onto a target having an actuatable aperture body and a divergence unit.

Figure 4 is an example of apparatus for directing laser radiation onto a target having an actuatable divergence unit.

Figure 5 is an example of apparatus for directing laser radiation onto a target of the type depicted in Figure 1 having a beam splitting arrangement configured to direct a plurality of sub-beams onto the target.

The present disclosure relates to apparatus 1 for directing laser radiation onto a target. Examples are depicted in Figures 1 and 3-5.

The apparatus 1 comprises a laser 2. The laser 2 generates a first beam 21 of radiation. The laser may take various forms. In some arrangements, the laser 2 comprises or consists of a solid-state laser, preferably a diode-pumped solid-state (DPSS) laser. A wide range of laser parameters may be used, including for example pulse lengths in a range from the order of a femto-second to the order of micro-seconds and/or wavelengths in a range from the far IR to D UV, preferably with pulse lengths of the order of pico-seconds or nano-seconds and/or wavelengths in the UV or green spectrum.

The apparatus 1 comprises a beam adjusting arrangement 30. The beam adjusting arrangement 30 adjusts the first beam 21 to provide a second beam 22. The beam adjusting arrangement 30 comprises at least an aperture body 31. The aperture body 31 defines an aperture for transmitting the second beam 22. The aperture body 31 removes (e.g., blocks, absorbs and/or reflects) a portion of the first beam 21 to provide the second beam 22. For example, as depicted schematically in Figure 1, a cross-section of the first beam 21 at the aperture body 31 may be larger than the aperture of the aperture body 31. The aperture may for example be circular and a diameter of the aperture may be smaller than a cross-sectional diameter of the first beam 21 at the aperture body 21. A portion of the first beam 21 may thus be blocked, absorbed and/or reflected by the aperture body 31, thereby removing that portion of the first beam 21. The removed portion may be a radially outermost portion of the first beam 21.

The apparatus 1 comprises a downbeam optical system 40. The downbeam optical system 40 is configured to direct the second beam 22, or a plurality of sub-beams 221-223 derived from the second beam 22, onto a target 12. The downbeam optical apparatus 40 may comprise all elements configured to influence the beam along the beam path between the aperture body 31 and the target 12. The examples of Figures 1, 3 and 4 depict cases where the downbeam optical system 40 directs the second beam 22 onto the target 12. Figure 5 depicts a case where the downbeam optical system 40 directs a plurality of sub-beams 221-223 onto the target 12. Although depicted with a single second beam 22 impinging on the target 12, any of the arrangements discussed with reference to Figures 1, 3 and 4 may be adapted to direct a plurality of sub-beams 221-223 onto the target 12, for example in the manner described below with reference to Figure 5. Further details of example configurations of the downbeam optical system 40 are provided later in the

disclosure.

The beam adjusting arrangement 30 is configured to provide dynamic adjustment of a cross-sectional intensity profile at the target 12 of the second beam 22, or of the plurality of sub-beams 221-223 derived from the second beam 22, by dynamically varying a proportion of the first beam 21 that is removed by the aperture body 31, by dynamically varying a divergence of the second beam 22 at the aperture body 31, or by dynamically varying both (i.e., the proportion of the first beam 21 that is removed by the aperture body 31 and the divergence of the second beam 22 at the aperture body 31). The dynamic adjustment comprises adjusting as a function of time. The adjustment may be varied continuous or in steps or both. As an example of stepped operation, the target 12 may be processed at one or more locations on the target 12 with a beam spot having a first intensity profile (which is constant during this processing) and, subsequently, the target 12 may be processed at one or more different locations with a beam having a second intensity profile (which is constant during the processing and different from the first intensity profile). The dynamic adjustment provided by the apparatus 1 allows rapid switching between the first intensity profile and the second intensity profile. The processing of the target 12 in each case may comprise drilling of holes in the target 12, optionally with different sizes for the two different intensity profiles.

Varying the proportion of the first beam 21 that is removed may lead to a corresponding variation in a spot size of illumination on the target 12: increasing the proportion may be used to reduce the spot size and decreasing the proportion may be used to increase the spot size. Varying the divergence of the second beam 22 at the aperture body 31 may also lead to a variation in the spot size. For example, increasing the divergence of the second beam 22 may be used to increase the spot size and decreasing the divergence of the second beam 22 may be used to decrease the spot size.

Alternatively or additionally, varying the proportion of the first beam 21 that is removed may be used to change a shape of the intensity profile.

Figures 2(a)-(c) depict example cross-sectional intensity profiles 20 for the second beam 22 applied as a circular beam spot on the target. The vertical axis in each case represents intensity (labelled -Intl and the horizonal axis represents radial distance (r) from a centre of the beam spot. In this example, the first beam 21 impinges on the aperture of the aperture body 31 with a Gaussian or Gaussian-like form and the aperture 31 provides a sharp cut off in the intensity profile 20 at a radius Rc. Figure 2(a) depicts a case where the aperture is relatively small compared with the size of the first beam 21 at the aperture body 31 such that the intensity profile 20 is cut off at a relatively low radius Re. Figure 2(c) represents a case where the aperture is relatively large compared with the size of the first beam 21 at the aperture body 31 such that a large portion of the radiation in the first beam 21 passes through the aperture to form part of the second beam 22. Figure 2(b) represents an intermediate case between the two situations of Figures 2(a) and 2(c). In each case, it can be seen that the intensity profile 20 is made more uniform by the action of the aperture relative to the Gaussian or Gaussian-like form of the beam output from the laser 2. An intensity profile of the second beam 22 thus more closely resembles a top-hat intensity profile 20 than an intensity profile of the first beam 21. This may provide advantageous performance, particularly in the context of laser drilling into the target 12. For example, arranging for a spot to have a near top-hat intensity profile may promote sharper cutting edges and/or avoid the need for excessively large peak intensities in the centre of the spot to ensure drilling of a hole to a desired diameter. More generally, different applications will require and/or benefit from different degrees of uniformity (closeness to top hat form) and it is therefore advantageous to be able to switch easily and/or quickly between the different degrees of uniformity. The switching may be done while keeping the spot size the same or while varying the spot size. The switching can be achieved in various ways according to embodiments of the disclosure. For example, it is possible to switch between top-hat and Gaussian profiles by moving the aperture in/out of the beam (i.e., along the beam path), or by increasing the aperture size, and/or by adjusting the lenses in the system.

In some arrangements, the beam adjusting arrangement 30 is configured to dynamically vary the proportion of the first beam 21 that is removed by the aperture body 31 by dynamically varying a cross-sectional size of the first beam 21 at the aperture body 31. The cross-sectional size of the first beam 21 may be defined in various ways. For example, the cross-sectional size may be defined as the cross-sectional area that contains substantially all of the intensity of the first beam 21 or all of a predetermined percentage of the intensity of the first beam 21 (e.g., 99%, 95%, or 90%). In one class of arrangement, this is at least partially achieved by moving the aperture body 31 along a beam path of the first beam 21 in combination with arranging for the first beam to impinge on the aperture body in a diverging or converging (non-collimated) form. This may be achieved for example by configuring the laser 2 to output a diverging beam (as depicted in Figure 1), or by providing a divergence unit 32 (described below) between the aperture body 31 and the laser 2 (as depicted in Figures 3 and 4). The apparatus 1 thus directs the first beam 21 in a diverging or converging form onto the aperture body 31. The beam adjusting arrangement 30 comprises an aperture body actuator 311 configured to drive movement of the aperture body 31 along the beam path of the first beam 21. It will be understood that "beam path" here corresponds to the beam path adjacent to the aperture body 31. The beam path may, for example, by substantially perpendicular to a plane of the aperture body 31. In such arrangements, the beam adjusting arrangement 30 varies the cross-sectional size of the first beam 21 at the aperture body 31 at least partially (e.g., exclusively or partially) by driving movement of the aperture body 31 using the aperture body actuator 311.

In an arrangement, the aperture body actuator 311 comprises a motor for driving movement of the aperture body 31. The aperture body actuator 311 may further comprise a controller for controlling the motor. The aperture body actuator 311 may, for example, be implemented using components (e.g., a motor and/or controller) of a computer numerical control (CNC) machine. The aperture body actuator 311 may be configured to move the aperture body 31 such as to vary a distance between the aperture body 31 and the laser 2 (measured along a beam path of the first beam 21). Moving the aperture body 31 progressively forwards along the beam path (i.e., such as to be progressively further from the laser 2 along the beam path) may cause the intensity profile of the second beam 22 to be the result of progressively cutting off more of the Gaussian profile of the first beam 21, thereby transitioning for example from an intensity profile of Figure 2(c) to the intensity profile of Figure 2(b) and, subsequently, to the intensity profile of Figure 2(a).

In some arrangements, as exemplified in Figures 3 and 4, the beam adjusting arrangement 30 comprises a divergence unit 32. The divergence unit 32 imparts and/or adjusts divergence in the first beam 21 in a portion of a beam path of the first beam 21 upbeam of the aperture body 31. In the example shown, the beam adjusting arrangement 30 also comprises an aperture body actuator 311 configured to drive movement of the aperture body 31. The aperture body actuator 311 may be configured and/or arranged to operate in any of the ways described above with reference to Figure 1. Imparting and/or adjusting the divergence of the first beam 21 affects the size of the first beam 21 at the aperture body 31 and thus affects the proportion of the first beam 21 that is removed by the aperture body 31. The divergence unit 32 can thus be used to set or control the proportion of the first beam 21 that is removed by the aperture body 31. Imparting and/or adjusting the divergence of the first beam 21 also affects the divergence of the second beam 22 at the aperture body 31. The divergence unit 32 can thus be used to set or control the divergence of the second beam 22 at the aperture body 31.

In the example of Figure 3, the divergence unit 32 has fixed properties. The divergence unit 32 may allow a divergence to be set more flexibly than may be possible when relying exclusively on the laser 2 to provide the divergence (as in Figure 1). In arrangements of this type, with such a fixed divergence unit 32, moving the aperture body 31 progressively forwards along the beam path (further from the laser 2 and the divergence unit 32) may cause the intensity profile of the second beam 22 to be the result of progressively cutting off more of the Gaussian profile of the first beam 21, thereby transitioning for example from an intensity profile of Figure 2(c) to the intensity profile of Figure 2(b) and, subsequently, to the intensity profile of Figure 2(a). The behaviour is thus similar to the situation in the arrangement of Figure 1.

In some arrangements, as exemplified in Figure 4, the beam adjusting arrangement 30 comprises a divergence unit actuator 321. The divergence unit actuator 321 is configured to adjust a divergence contributed by the divergence unit 30. The divergence unit actuator 321 may be used to control the proportion of the first beam 21 that is removed by the aperture body 31 and/or the divergence of the second beam 22 at the aperture body 31.

In some arrangements, the divergence unit actuator 321 is configured to drive movement of the divergence unit 32 to vary a separation between the divergence unit 32 and the aperture body 31. In cases where the first beam 21 diverges between the divergence unit 32 and the aperture of the aperture body 31, moving the divergence unit 32 closer to the aperture body 31 will typically lower the proportion of the first beam 21 that is removed by the aperture body 31 and increase the divergence of the second beam 22 at the aperture body 31. Moving the divergence unit 32 closer to the aperture body 31 may have an effect similar to moving the aperture body 31 backwards along the beam path in arrangements of the type described above with reference to Figure 1 and 3 (causing the intensity profile to transition for example from a form similar to Figure 2(a) to a form similar to Figure 2(b) and, subsequently, to a form similar to Figure 2(c)). The movement may also increase the spot size. Conversely, increasing a separation between the divergence unit 32 and the aperture body 31 will tend to cause to an opposite progression in the shape of the intensity profile (e.g., from Figure 2(c) to Figure 2(b) and, subsequently, to Figure 2(a)) and/or to a decrease in the spot size.

Alternatively or additionally, in some arrangements, as depicted in Figure 4, the divergence unit 32 comprises two or more optical components 322, 323 (e.g., lenses) configured such that a divergence contributed by the divergence unit 32 can be varied by changing a positioning of the optical components 322, 323 relative to each other, such as a separation between two of the optical components 322, 323 (as depicted schematically in Figure 4). For example, the divergence unit 32 may comprise optical components 322, 323 defining telescope optics and the divergence contributed by the divergence unit 32 may be controlled by changing a separation between the optical components 322, 323 that define the telescope optics. The divergence unit 32 may, for example, drive movement of either or both of the optical components 322, 323 to change the separation between them. In an arrangement, the beam adjusting arrangement 30 varies the cross-sectional size of the first beam 21 at the aperture body 31 at least partially by varying a divergence of the first beam 21 using the divergence unit actuator 321.

In an arrangement, the divergence unit actuator 321 comprises a motor for driving movement of the divergence unit 32 and/or of one or more optical components in the divergence unit 32. The divergence unit actuator 321 may comprise a controller for controlling the motor. The divergence unit actuator 321 may, for example, be implemented using components (e.g., a motor and/or controller) of a computer numerical control (CNC) manufacturing machine. One or more components (e.g., the controller) of the divergence unit actuator 321 may be shared with the aperture body actuator 311. Thus, a common controller may be used to control the aperture body 31 and the divergence unit 32. Progressively increasing a size of the first beam 21 impinging on the aperture body 31, for example by progressively increasing a divergence contributed by the divergence unit 32 may cause the intensity profile of the second beam 22 to be the result of progressively cutting off more of the Gaussian profile of the first beam 21, thereby transitioning for example from an intensity profile of Figure 2(c) to the intensity profile of Figure 2(b) and, subsequently, to the intensity profile of Figure 2(a).

The downbeam optical system 40 may take various forms. In some arrangements, the downbeam optical system 40 is configured to perform infinity imaging of the aperture in the aperture body 31 onto the target 12.

In some arrangements, as exemplified in Figures 1 and 3-5, the downbeam optical system 40 comprises a variable focal length image relay 41. The image relay 41 comprises a plurality of optical components 412 and 413 (e.g., lenses). For example, the image relay 41 may be a two-lens image relay 41. One or more of the optical components may be configured to be moveable to vary the properties of the image relay 41. The properties of the image relay 41 may, for example, be varied to change a magnification provided by the image relay 41 to vary a size of the image of the aperture on the target 12 (e.g., by changing a focal length of the image relay 41) and/or to adapt to changes in the position of the aperture body 31 (e.g., by moving the image relay 41 and/or changing the focal length of the image relay 41 to keep the aperture body 31 a focal length away from the image relay 41).

As discussed above, the proportion of the first beam 21 that is removed by the aperture body 31 (determined for example by the ratio between the aperture diameter and the beam diameter at the aperture) is variable, for example by changing the position of the aperture 31. The aperture defines an object to be imaged on the target 12 and thereby defines the object plane. The downbeam optical system 40 is configured to form an image of this object (the aperture) on the target 12.

The image relay 41 has an effective focal length (e.g., considering the group of lenses forming the image relay 41 as a single lens). The distance between the aperture body 31 (object plane) and the image relay 41 should be close or identical to the focal length of the image relay 41. If the target 12 is positioned at the focus of a lens system 44, 44', 44" (see below) downbeam of the image relay 41, the image relay 41 and the lens system 44, 44', 44" implement infinity imaging of the aperture on the target 12. In this case, the imaging of the aperture onto the target 12 is insensitive to the length of the optical path between the image relay 41 and the lens system 44, 44', 44". As described below, this property may be exploited to form multiple images of the aperture on the target via separate sub-beams that follow optical paths of different lengths to the target 12.

Changing the separation of lenses 412 and 413 in the image relay 41 changes the focal length (and position) of the image relay 41. As mentioned above, this can be used to control the magnification of the system. The magnification is the ratio between the focal lengths of the image relay 41 and lens system 44, 44', 44" downbeam.

In some arrangements, as exemplified in Figures 1, 3, 4 and 5, the apparatus 1 comprises a relay actuator 411. The relay actuator 411 may be configured to adjust a magnification applied by the image relay 41. The relay actuator 411 may thus be used to control a magnification of an image of the aperture on the target 12. Additionally or alternatively, the relay actuator 411 may be used to adapt to changes in the position of the aperture body 31 to keep the aperture body 31 a focal length away from the image relay 41.

In an arrangement, the relay actuator 411 comprises a motor for driving movement of one or more of the optical components 412, 413 of the image relay 41. The relay actuator 411 may comprise a controller for controlling the motor. The relay actuator 411 may, for example, be implemented using components (e.g., a motor andior controller) of a computer numerical control (CNC) manufacturing machine. One or more components (e.g., the controller) of the relay actuator 411 may be shared with either or both of the aperture body actuator 311 and the divergence unit actuator 321. Thus, a common controller may be used to control two or more of the aperture body 31, the divergence unit 32, and the image relay 41.

In some arrangements, as exemplified in Figures 1, 3 and 4, the downbeam optical system 40 further comprises a mirror 42 for redirecting the second beam 22 towards the target 12. The minor 42 provides flexibility for positioning components upbeam of the mirror 42, such as by avoiding the need for all components to be in line with a beam path of the second beam 22 downbeam of the mirror 42. This may facilitate compactness of the apparatus 1, at least in the direction perpendicular to the target 12.

In some arrangements, as exemplified in Figures 1 and 3-5, the downbeam optical system 40 comprises one or more scanners 43, 43', 43". The provision of scanners is optional. Where provided, the or each scanner 43, 43', 43" may comprise a galvo scanner.

The or each scanner 43, 43', 43" may thus be configured to control a position of a beam spot on the target 12. The or each scanner 43, 43', 43" may control the positions and/or orientations of one or more internal mirrors to steer the second beam 22 or a respective sub-beam 221-223, for example to move a beam spot through a sequence of desired locations on the target 12.

In some arrangements, as exemplified in Figures 1 and 3-5, the downbeam optical system 40 comprises one or more lens systems 44, 44', 44". The provision of such lens systems is optional. Where provided, the or each lens system 44, 44', 44" may be configured to project (e.g., focus) the second beam 22 or a respective sub-beam 221-223 onto the target 12, for example as a respective beam spot. In some arrangements, the or each lens system 44, 44', 44" is configured to operate as an F-theta lens. The or each lens system 44, 44', 44" may be provided between the target 12 and a respective scanner 43, 43', 43". For infinity imaging the target is placed at the focal plane of the F-theta lens. As described above, infinity imaging may be implemented by positioning the aperture body 31 such that a distance between the aperture body 31 and the image relay 41 is close or equal identical to the focal length of the image relay 41 and positioning the target 12 such that a distance between the target 12 and the lens system 44, 44', 44" is close or equal to the focal length of the lens system 44, 44', 44".

In some arrangements, the downbeam optical system 40 comprises a beam splitting arrangement configured to split the second beam 22 to provide the plurality of sub-beams 221-223 derived from the second beam 22. An example configuration is depicted in Figure 5. The beam splitting arrangement in this case comprises a plurality of beam splitters 45, 45' and a mirror 42. Each beam splitter redirects a portion of the second beam 22 to generate a sub-beam. In the example shown, a first beam splitter 45 generates sub-beam 221, a second beam splitter 45' generates sub-beam 222, and a mirror 42 generates sub-beam 223. The provision of three sub-beams 221-222 is purely exemplary. Fewer than or more than three sub-beams may be provided. The number of beam splitters may thus be varied accordingly. Splitting the second beam 22 into multiple sub-beams allows multiple different regions on the target 12 to be processed simultaneously, thereby improving throughout. For example, multiple different indentations or holes may be simultaneously drilled into the target 12 at different locations. Implementing infinity imaging is particularly desirable in arrangements involving beam splitting (e.g., such as that of Figure 5) because the infinity imaging allows a high-quality image of the aperture to be formed on the target 12 in a way that is not affected by the different path lengths between the image relay 41 and the target 12 for the different respective sub-beams 221-223 The apparatus 1 for directing laser radiation onto a target according to any of the arrangements described herein may in principle be used in a variety of contexts where it is desired to quickly and flexibly vary the size and/or shape of an intensity profile of a beam spot on a target. The apparatus 1 is, however, particularly well suited when configured to operate as a laser drilling apparatus. A laser drilling apparatus may thus be provided that comprises or consists of the apparatus 1 according to any of the arrangements described herein.

Embodiments of the disclosure may also be implemented as methods. Thus, there may be provided a method of directing laser radiation onto a target. The method comprises using a laser to generate a first beam of radiation; using an aperture body to adjust the first beam to provide a second beam, the aperture body defining an aperture for transmitting the second beam and acting to remove a portion of the first beam to provide the second beam; and directing the second beam, or a plurality of sub-beams derived from the second beam, onto the target. The method comprises dynamically adjusting a cross-sectional intensity profile at the target of the second beam, or of the plurality of sub-beams derived from the second beam, by dynamically varying: a proportion of the first beam that is removed by the aperture body; and/or a divergence of the second beam at the aperture body. The method may use any of the apparatus configurations described above. Additionally or alternatively, there may be provided a method of removing material from a target by laser drilling. The method comprises performing laser drilling by directing laser radiation onto the target using any of the methods and apparatus configurations described above.

Claims

CLAIMS1. An apparatus for directing laser radiation onto a target, comprising: a laser configured to generate a first beam of radiation; a beam adjusting arrangement configured to adjust the first beam to provide a second beam, wherein the beam adjusting arrangement comprises an aperture body defining an aperture for transmitting the second beam, the aperture body being configured to remove a portion of the first beam to provide the second beam; and a downbeam optical system configured to direct the second beam, or a plurality of sub-beams derived from the second beam, onto the target, wherein the beam adjusting arrangement is configured to provide dynamic adjustment of a cross-sectional intensity profile at the target of the second beam, or of the plurality of sub-beams derived from the second beam, by dynamically varying: a proportion of the first beam that is removed by the aperture body; and/or a divergence of the second beam at the aperture body.
2. The apparatus of claim 1, wherein the beam adjusting arrangement is configured to dynamically vary the proportion of the first beam that is removed by the aperture body by dynamically varying a cross-sectional size of the first beam at the aperture body.
3. The apparatus of claim 2, wherein the beam adjusting arrangement comprises an aperture body actuator configured to drive movement of the aperture body along a beam path of the first beam.
4. The apparatus of claim 3, wherein the beam adjusting arrangement is configured to vary the cross-sectional size of the first beam at the aperture body at least partially by driving movement of the aperture body using the aperture body actuator.
5. The apparatus of any preceding claim, wherein the apparatus is configured to direct the first beam in a diverging or converging form onto the aperture body.
6. The apparatus of any preceding claim, wherein the beam adjusting arrangement comprises a divergence unit configured to impart and/or adjust divergence in the first beam in a portion of a beam path of the first beam upbeam of the aperture body.
7. The apparatus of claim 6, wherein the beam adjusting arrangement comprises a divergence unit actuator configured to adjust a divergence contributed by the divergence unit.
8. The apparatus of claim 7, wherein the beam adjusting arrangement is configured to vary the cross-sectional size of the first beam at the aperture body at least partially by varying a divergence of the first beam using the divergence unit actuator.
9. The apparatus of claim 7 or 8, wherein the divergence unit comprises two or more optical components configured such that a divergence contributed by the divergence unit can be varied by changing a positioning of the optical components relative to each other.
10. The apparatus of claim 9, wherein the divergence unit actuator is configured to drive movement of one or more of the optical components to vary the positioning of the optical components relative to each other.
11. The apparatus of any of claims 6 to 10, wherein the divergence unit actuator is configured to drive movement of the divergence unit to vary a separation between the divergence unit and the aperture body.
12. The apparatus of any of claims 6 to 11, wherein the divergence unit comprises telescope optics.
13. The apparatus of any preceding claim, wherein the downbeam optical system comprises a beam splitting arrangement configured to split the second beam to provide the plurality of sub-beams derived from the second beam.
14. The apparatus of any preceding claim, wherein the downbeam optical system is configured to form an image of the aperture on the target.
15. The apparatus of claim 14, wherein the downbeam optical system comprises a variable focal length image relay and the aperture body is positioned such that a distance between the aperture body and the image relay is close or identical to a focal length of the image relay.
16. The apparatus of claim 15, wherein the apparatus is configured to adjust the position and/or focal length of the image relay in response to changes in position of the aperture body.
17. The apparatus of claim 15 or 16, wherein the downbeam optical system comprises a lens system positioned such that a distance between the lens system and the target is equal to a focal length of the lens system.
18. The apparatus of claim 17, wherein the image relay and the lens system are configured to perform infinity imaging of the aperture on the target, such that the forming of the image of the target is insensitive to a length of the optical path between the image relay and the lens system.
19. A laser drilling apparatus configured to remove material from a target by laser drilling, the laser drilling apparatus comprising the apparatus of any preceding claim.
20. A method of directing laser radiation onto a target, the method comprising: using a laser to generate a first beam of radiation; using an aperture body to adjust the first beam to provide a second beam, the aperture body defining an aperture for transmitting the second beam and acting to remove a portion of the first beam to provide the second beam; and directing the second beam, or a plurality of sub-beams derived from the second beam, onto the target, wherein the method comprises dynamically adjusting a cross-sectional intensity profile at the target of the second beam, or of the plurality of sub-beams derived from the second beam, by dynamically varying: a proportion of the first beam that is removed by the aperture body; and/or a divergence of the second beam at the aperture body.
21 A method of removing material from a target, comprising performing laser drilling by directing laser radiation onto the target using the method of claim 20.