Laser processing method and laser processing apparatus

Abstract

Laser processing methods and apparatus are disclosed. In one arrangement, a method comprises using a laser beam to modify a sample along a processing trajectory in the sample by focusing the laser beam through a first face of the sample to a laser focus in the sample and providing relative movement between the laser focus and the sample to move the laser focus along the processing trajectory. The processing trajectory comprises a proximal portion and a distal portion. The proximal portion is nearer to a second face of the sample than the distal portion. The method comprises interacting with or adjusting the laser beam during processing of the proximal portion to reduce or prevent impingement of the laser beam onto the second face during the processing of the proximal portion.

Description

[0001] LASER PROCESSING METHOD AND LASER PROCESSING APPARATUS

[0002] The present disclosure relates to laser processing methods and apparatus.

[0003] Laser writing can be used to form patterns or tracks in samples such as glass chips. Laser writing can be used to form waveguides for example. Laser writing at or near peripheral edges can be challenging due to aberrations in laser focus caused by the laser light impinging simultaneously onto non-parallel surfaces of the sample (e.g., onto a portion of an upper side of the sample and a portion of a peripheral edge of the sample). Such aberrations make it difficult or impossible to form waveguides right up to the edge of the sample because the aberrations reduce the laser focus intensity. Reducing the laser focus intensity reduces the light matter interaction and causes the waveguide structural modification to fade away near the edge of the sample. This makes it very inefficient to then couple light into the waveguide from an external optical fibre, as there is a large distance (exceeding 10 m, beyond the Rayleigh range) from the fibre to the waveguide core. A solution to this issue is to polish the samples back after waveguide writing to reveal the fully formed waveguide at the sample edge. However, this is time consuming, inefficient and impractical for situations where samples are already fixed in place.

[0004] It is an object of the invention to at least partially address one or more of the issues mentioned above or other issues.

[0005] According to an aspect of the invention, there is provided a laser processing method, comprising: using a laser beam to modify a sample along a processing trajectory in the sample by focusing the laser beam through a first face of the sample to a laser focus in the sample and providing relative movement between the laser focus and the sample to move the laser focus along the processing trajectory, wherein: the processing trajectory comprises a proximal portion and a distal portion, the proximal portion being nearer to a second face of the sample than the distal portion; and the method comprises interacting with or adjusting the laser beam during processing of the proximal portion to reduce or prevent impingement of the laser beam onto the second face during the processing of the proximal portion.

[0006] By suppressing impingement on the second face it is possible to reduce or avoid disruption of the laser focus in the proximal region near to the second face and thereby allow processing of the processing trajectory to be performed closer to the second edge or even to intersect with the second edge. Laser processing can thus form structures such as waveguides at or close to edges with fewer or no requirements for edges to be polished back after laser processing. This may improve throughput of, and / or simplify, a manufacturing process. The approach may also increase the range of situations in which laser writing to edges can be performed, such as where a sample is already installed in a location where polishing cannot easily be performed.

[0007] Optionally, the method further comprises controlling the laser beam to form a continuously modified region extending along the first processing trajectory from the proximal portion to the distal portion; and / or controlling the laser beam to form a sequence of spatially separated modified regions along the first processing trajectory.

[0008] Optionally, the method further comprises increasing a power of the laser beam during the interaction with or adjustment of the laser beam to at least partially compensate for the interaction or adjustment. The power may be adjusted, for example, to maintain the same fluence at the laser focus during processing of the proximal portion compared to processing of the distal portion.

[0009] Optionally, the interaction or adjustment comprises suppressing a contribution to the laser focus from a portion of the laser beam. Suppressing a contribution to the laser focus from a portion of the laser beam can be implemented easily and controllably.

[0010] Optionally, the portion of the laser beam is suppressed using a beam modifying element in a path of the laser beam. The beam modifying element may, for example, be configured to block the portion of the laser beam. Blocking a portion of a laser beam can be implemented easily and with high precision.

[0011] Optionally, the beam modifying element is configured to be switched between a first state and one or more second states. The first state is such that the beam modifying element does not suppress the portion of the laser beam. Each second state is such that the beam modifying element does suppress at least part of the portion of the laser beam. Allowing the beam modifying element to be switched between different states allows an interaction with the laser beam to prevent or reduce impingement on the second face to being controlled so as to be applied only when needed and / or only to the extent that is needed. This may avoid unnecessary wastage of laser energy when an increase in power is required to compensate for the interaction, such as where the interaction comprises blocking of a portion of the laser beam.

[0012] Optionally, the beam modifying element is maintained in the first state during processing of the distal portion and is switching into one or more of the second states during processing of the proximal portion. The one or more second states may comprise a single second state and the single second state is maintained during all of the processing of the proximal portion. Using only a single second state facilitates operation and / or simplifies construction.

[0013] Optionally, the one or more second states comprises a plurality of second states or a continuum of second states and the beam modifying element is switched through the second states to progressively suppress an increasing proportion of the portion of the laser beam as the laser focus approaches the second face during processing of the proximal portion. Progressively switching the beam modifying element in this manner allows the laser beam to be adjusted progressively to the extent require to achieve a desired reduction or avoidance of impingement of the laser beam on the second face, thereby avoiding overadjustment and / or reducing any requirement for compensatory increases in laser power.

[0014] Optionally, the switching is performed at least partly by moving the beam modifying element relative to the laser beam. This approach can be implemented using simple hardware with high accuracy.

[0015] Optionally, the beam modifying element comprises a spatial light modulator and the switching is performed at least partly by changing a state of the spatial light modulator. This approach provides a high degree of flexibility for adjustment, as well as promoting robustness and / or compactness as the beam modifying element no longer needs to be moveable as a whole.

[0016] Optionally, the interaction with or adjustment of the laser beam comprises changing an average direction of propagation of the laser towards the sample. This approach allows impingement on the second face to be reduced or avoided without removing any power from the laser beam. This approach may therefore reduce or eliminate a need to increase a power of the laser to compensate for the interaction or adjustment that reduces or avoids impingement on the second face. According to an aspect of the invention, there is provided a laser processing method, comprising: using a laser beam to modify a sample by focusing the laser beam through a first face of the sample to a laser focus in the sample, wherein the sample comprises a proximal portion and a distal portion, the proximal portion being nearer to a second face of the sample than the distal portion; and the method comprises suppressing a contribution to the laser focus from a portion of the laser beam when the laser is focused to a laser focus within the proximal portion to reduce or prevent impingement of the laser beam onto the second face.

[0017] According to an aspect of the invention, there is provided a laser processing apparatus, comprising: a laser configured to generate a laser beam; a sample support configured to support a sample; a lens configured to focus the laser beam onto the sample; a beam adjuster configured to adjust a configuration of the laser beam; and a control system configured to control the laser, the sample support, and the beam adjuster, to: modify a sample along a processing trajectory in the sample by focusing the laser beam through a first face of the sample to a laser focus in the sample and provide relative movement between the laser focus and the sample to move the laser focus along the processing trajectory, wherein: the processing trajectory comprises a proximal portion and a distal portion, the proximal portion being nearer to a second face of the sample than the distal portion; and the control system is configured to control the laser and / or the beam adjuster to interact with or adjust the laser beam during processing of the proximal portion to reduce or prevent impingement of the laser beam onto the second face during the processing of the proximal portion.

[0018] Embodiments of the disclosure will be further described by way of example only with reference to the accompanying drawings.

[0019] Figure l is a schematic side sectional view depicting processing of a central region of a sample using a laser beam to create a laser modified region along a processing trajectory.

[0020] Figure 2 is a schematic side sectional view depicting the processing of Figure 1 at a later stage of the processing trajectory in a peripheral region of the sample, illustrating impingement of the laser beam on a side face of the sample.

[0021] Figure 3 is a schematic side sectional view depicting a laser processing apparatus. Figures 4-6 are schematic side sectional views of a portion of the laser processing apparatus of Figure 3 adjacent to the sample, depicting different stages of processing of a processing trajectory through a first face of the sample, Figure 4 showing processing without any interaction with the beam, and Figures 5 and 6 showing processing with a beam modifying device interacting with the beam.

[0022] Figures 7-9 show cross-sections of the laser beam relative to plane A-A respectively for the configurations shown in Figures 4-6.

[0023] Figures 10-12 are schematic side sectional views of a portion of the laser processing apparatus of Figure 3 adjacent to the sample, depicting different stages of processing of a processing trajectory through a first face of the sample in which the laser is controlled such that processing takes place within discrete portions of the processing trajectory, Figure 10 showing processing in one of the discrete portions without any interaction with the beam, Figure 11 showing processing outside of the discrete portions, and Figure 12 showing processing in another of the discrete portions with a beam modifying device interacting with the beam.

[0024] Figures 13-15 are schematic side sectional views of a portion of the laser processing apparatus of Figure 3 adjacent to the sample, depicting different stages of processing of a processing trajectory through a first face of the sample in which there is a beam modifying device interacting with the beam in multiple regions along the processing trajectory, Figure 13 showing processing within a first region with a beam modifying device interacting with the beam, Figure 14 showing processing within a second region without any interaction with the beam, and Figure 15 showing processing within a third region with a beam modifying device interacting with the beam.

[0025] Figures 16-18 are a schematic side sectional view showing a variation on the arrangement depicted in Figures 13-15 in which there is a beam modifying device interacting with the beam in the second region.

[0026] Figure 19 is a schematic side sectional view showing a variation on the arrangement depicted in Figures 4-9 in which a beam modifying device is attached to the sample.

[0027] Figure 20 is a schematic side sectional view depicted a further variation on the arrangement of Figures 4-10 in which adjustment to reduce or avoid impingement on the second face is implemented by adjusting an average direction of propagation of the laser beam towards the sample.

[0028] Figure 21 (main) shows a transmission light microscope image of a sample showing cross-sections of waveguides written at 500 microns depth viewed along their axes; Figure 21 (bottom left inset) depicts a waveguide coupled mode associated with the leftmost waveguide in Figure 21 (main); and Figure 21 (bottom right inset) depicts a waveguide coupled mode associated with the rightmost waveguide in Figure 21 (main).

[0029] Figure 22 depicts simulations of focussed laser intensity distributions for different configurations of blocking in the pupil plane looking along different directions; the simulations demonstrate that for half pupil blocking a laser power needs to be increased by a factor of 4 to recover the same intensity at the laser focus as is obtained using full pupil illumination.

[0030] Figures 23-26 show mode field diameter data for waveguides manufactured at various depths in fused silica and EAGLE 2000 samples with and without edge correction according to embodiments of the disclosure, and images of the mode sizes at the output facet of the samples.

[0031] Figures 27 and 28 show mode field diameter data for waveguides manufactured at various depths in fused silica and EAGLE 2000 samples with and without edge correction according to embodiments of the disclosure compared with the diameter of an optical fibre.

[0032] Figure 29 demonstrates the transmission coefficient between samples with waveguides and optical fibres for waveguides formed at various depths by traditional methods and methods according to embodiments of the disclosure.

[0033] Embodiments of the present disclosure relate to a laser processing method and a laser processing apparatus. The laser processing apparatus may be configured to perform the laser processing method.

[0034] Figures 1 and 2 illustrate traditional laser writing of a waveguide 8 in a sample 6. A lens 2 is used to focus a laser beam 4 through a top face 5 of a sample 6 to a laser focus at a desired depth within the bulk of the sample 6. A fluence at the focus of the laser beam is sufficient to locally modify material of the sample 6 and thereby form the waveguide 8. Typically, the laser would be kept stationary while the sample 6 is translated underneath the laser such that the laser focus traces out the desired shape of the waveguide 8. Figure 1 shows a stage of such a process where the laser is processing a central region of the sample 6 that is distal from any of the side faces, such as side face 9. At this stage of the process, the laser impinges exclusively on the planar top face 5 and a high quality focus can be formed easily at the desired depth.

[0035] Figure 2 shows a later stage of the process when the laser is processing a peripheral region of the sample 6. At this stage, the sample 6 is positioned such that the laser simultaneously impinges both on the top face 5 and on the side face 9. This disrupts the quality of the focus and prevents formation of the waveguide in the region adjacent to the side face 9. As mentioned in the introductory part of the description, a solution to this problem is to polish back the side face 9 after the laser processing, but this has various shortcomings.

[0036] Methods and apparatus described below address these issues by allowing laser processing to be performed effectively closer to or even up to the edge of a sample.

[0037] Figure 3 schematically depicts a laser processing apparatus 10.

[0038] The apparatus 10 comprises a laser 12 configured to generate a laser beam 14. Any laser suitable for providing the processing described below may be used. In one example implementation, a 515nm wavelength laser having a 1MHz pulse repetition rate and pulse duration of 170fs was used, but lasers having other wavelengths, other pulse repetition rates and / or other pulse durations may be used.

[0039] The apparatus 10 comprises a sample support 16 configured to support a sample 18. The sample support 16 may be configured to be moveable. The sample support 16 may, for example, be motorised. The sample 18 may take any suitable form. In one example implementation a borosilicate glass was used but other compositions of glass or other materials are possible.

[0040] The apparatus 10 comprises a lens 20 configured to focus the laser beam 14 onto the sample 18. Any suitable optical arrangement may be used to provide the lensing functionality. In one example implementation, a microscope objective lens having a numerical aperture of 0.5 and 20x magnification was used.

[0041] The apparatus 10 comprises a beam adjuster 22 configured to adjust a configuration of the laser beam 14. The beam adjuster 22 may interact with the laser beam 14 to change one or more properties of the laser beam or otherwise adjust the laser beam 14. Further details about example implementations of the beam adjuster 22 are described below with reference to Figures 4-11.

[0042] The apparatus 10 further comprises a control system 24 configured to control the laser 12 (e.g., to control a power of the laser), the sample support 16 (e.g., to move the sample 18), and the beam adjuster 22 (e.g., as described below) to implement any of the laser processing methods described below. The control system 24 may comprise any suitable combination of data processing hardware (e.g., CPUs, memory, data transmission lines, etc.), firmware, and / or software for performing the functionality required.

[0043] The control system 24 is configured to implement a laser processing method. The laser processing method comprises using the laser beam 14 to modify the sample 18 along a processing trajectory 26 in the sample 18. The sample 18 is modified by focusing the laser beam 14 through a first face 28 of the sample 18 to a laser focus 30 in the sample 18 and providing relative movement between the laser focus 30 and the sample 18 to move the laser focus 30 along the processing trajectory 26. The modification of the sample 18 may be such as to form a waveguide in the sample 18 along the processing trajectory 26, or may be such as to form spatially separated modified regions 26a along the processing trajectory 26, which may constitute regions of refractive index contrast and / or absorption. A range of speeds made be used for the relative movement. The sample 18 may typically be moved at a speed in the range of about Imm / s to about lOmm / s, such as in the range of about 4mm / s to about 8mm / s, such as around 6mm / s. A processing trajectory 26 is depicted schematically in Figure 3 at an intermediate processing stage where a portion 32 (hatched) of the processing trajectory 26 to the left of the laser focus 30 has been processed and a portion 33 to the right of the laser focus 30 is yet to be processed. In this example, the relative movement is provided by moving the sample support 16, for example via a motor, to the left relative to the laser 12. The processing trajectory 26 in this example follows a horizontal path parallel to a single direction of relative movement between the sample support 16 and the laser 12. The processing trajectory 26 may follow a path at a constant depth beneath the first face 28 of the sample 18. Alternatively, the processing trajectory 26 may comprise portions at different depths. The first face 28 in the example shown is a planar surface, which may be horizontal for example. The first face 28 is parallel to a direction of relative movement between the sample support 16 and the laser 12. In other examples, the processing trajectory 26 and / or first face 28 may be oriented differently (e.g., vertically or at an oblique angle relative to the vertical direction).

[0044] Figures 4-6 schematically depict processing of a sample 16 at three different time points along a processing trajectory 26. The processing trajectory 26 comprises a proximal portion 34 and a distal portion 36. The proximal portion 34 is nearer to a second face 38 of the sample 18 than the distal portion 36. Figure 4 depicts processing at a first time point when the laser focus 30 is within the distal portion 36 relatively far from the proximal portion 34. Figure 5 depicts processing at a second time point when the laser focus 30 is at a transition point on the border between the distal portion 36 and the proximal portion 34. Figure 6 depicts processing at a third time point when the laser focus 30 is within the proximal portion 34 and closer to the second face 38 than to the distal portion 36. Figures 7-9 show respective cross-sections A-A of the laser beam 14 downbeam of the lens 20. In Figure 7, which corresponds to the arrangement of Figure 4, the cross-section A-A is substantially circular. In Figures 8 and 9, which correspond respectively to Figures 5 and 6, the cross-section A-A is semi-circular due to blocking by a beam modifying element 40, as explained in further detail below. The semi-circular form is exemplary. Variations on the semi-circular form may be implemented, for example, to take account of the conical nature of the laser beam between the lens 20 and the sample 18.

[0045] The second face 38 is a face that is non-parallel to the first face 28. The second face 38 may, for example, comprise a peripheral edge of the sample 18. The second face 38 may be substantially planar, at least locally (e.g., in a region that would be traversed by an extrapolation of the processing trajectory 26 through the second face 38). The second face 38 may be substantially perpendicular to the first face 28, at least locally (e.g., in a region that would be traversed by an extrapolation of the processing trajectory 26 through the second face 38).

[0046] The method comprises interacting with or adjusting the laser beam 14 during processing of the proximal portion 34 to reduce or prevent impingement of the laser beam 14 onto the second face 38 during the processing of the proximal portion 34. The interaction with and / or adjustment of the laser beam 14 may be implemented by a beam adjuster 22.

[0047] In one class of implementation, the beam adjuster 22 suppresses a contribution to the laser focus 30 from a portion of the laser beam 14. The beam adjuster 22 may, for example, comprise a beam modifying element 40 positioned in a path of the laser beam 14. The beam modifying element 40 interacts with the laser beam 14 to suppress the contribution to the laser focus 30 from the portion of the laser beam 14. The beam adjuster 22 may be configured to control an interaction between the beam modifying element 40 and the laser beam 14.

[0048] In an example implementation, as exemplified in Figures 4-6, the beam modifying element 40 is configured to block the portion of the laser beam 14. The beam modifying element 40 may for example be formed from a material that is optically opaque with respect to the laser beam 14. The beam modifying element 40 may absorb and / or reflect a portion of the laser beam 14 that impinges on the beam modifying element 40. The blocked portion of the laser beam 14 may comprise or consist of a portion of the laser beam 14 that would have impinged on the second face 38 of the sample 18 had the portion not been blocked. This situation is illustrated in Figures 4-9. In the arrangement of Figure 4 it can be seen that the laser beam 14 is so far from the second face 38 that no blocking is necessary to prevent impingement onto the second face 38. In the arrangement of Figure 5, the laser beam 14 is still positioned such that blocking is not necessary to prevent impingement on the second face 38. However, it can be seen that if the right half of the cone of laser beam 14 between the lens 20 and the sample 18 were not blocked a rightmost edge of the laser beam 14 would be very close to impinging on the second face 38. Without blocking, any movement of the laser beam 14 to the right relative to the sample 18 would cause the laser beam 14 to start to impinge on the second face 38. This would disrupt the quality of the laser focus 30 and thereby disrupt processing of the processing trajectory 26. In the arrangement of Figure 6, the laser beam 14 is positioned such that there would be significant impingement of the laser beam 14 onto the second face 38 in the absence of blocking. According to the method of the present disclosure, the impingement of the laser beam 14 onto the second face 38 is reduced or blocked to prevent impingement onto the second face 38. In the example of Figures 4-9, a beam modifying element 40 is inserted into the laser beam 14 to block a portion of the laser beam 14 when the lens 20 is positioned as shown in Figure 5 relative to the sample 18 or at any position further to the right relative to the sample 18 (i.e., such that the blocking decreases or prevents impingement on the second face 38).

[0049] In some implementations, the suppressed portion of the laser beam 14 comprises at least 20% of a cross-section of the laser beam 14. Typically, as exemplified in Figures 4-9, the suppressed portion is substantially half the cross-section of the laser beam. In the example shown, the suppressed portion comprises a semi-cone of the laser beam 14 between the lens 20 and the sample 18. A semi-cone in this context is understood to mean half of a cone, with the cone cut through the tip of the cone along a plane parallel to the axis of the cone. Cross-sections of the semi-cone perpendicular to the axis are semicircular.

[0050] In some implementations, the interaction with or adjustment of the laser is such that the fluence of the laser beam impinging onto the second face during the processing of the proximal portion is reduced by at least 10%, optionally be at least 25%, optionally be at least 50%, optionally by at least 75%, optionally by at least 90% (relative to the case where the interaction with or adjustment of the laser beam is not performed).

[0051] The beam modifying element 40 may be moveably mounted relative to the laser beam 14. An actuation system 42 may be provided that is controllable by the beam adjuster 22. The actuation system 42 controllably moves the beam modifying element 40. The actuation system 42 may comprise any suitable combination of hardware, firmware and software for achieving this purpose, such as one or more motors, one or more sensors, data transmission lines, etc. The beam adjuster 22 may be configured to control a position of the beam modifying element 40 relative to the laser beam 14 to control an extent to which the laser beam 14 is blocked by the beam modifying element 40 at any particular time. For example, moving the beam modifying element 40 deeper into the beam path may block an increased proportion of a cross-section of the laser beam 14 and vice versa.

[0052] The beam modifying element 40 may be switchable between a first state and one or more second states. For example, the beam modifying element may be switched from the first state to the one or more second states.

[0053] The first state is such that the beam modifying element 40 does not suppress the portion of the laser beam 14. In the configuration of Figures 4-9, the first state may be implemented, for example, be controlling the actuation system 42 to position the beam modifying element 40 outside of the path of the laser beam 14, such as is shown schematically in Figure 4.

[0054] Each second state is such that the beam modifying element 40 does suppress at least part of the portion of the laser beam 14, for example by being positioned at least partly inside the path of the laser beam 14. the beam modifying element is maintained in the first state during processing of the distal portion and is maintained in one or more of the second states during processing of the proximal portion.

[0055] The one or more second states may comprise a single second state and the single second state may be maintained during all of the processing of the proximal portion 34. The example of Figures 4-9 is a configuration of this type. When the laser focus 30 reaches the transition point shown in Figure 5, the beam modifying element 40 is brought from a position entirely outside of the beam path (as shown in Figure 4) to a position where the beam modifying element 40 blocks half the laser beam, as depicted in the cross-sectional views perpendicular to plane A-A in Figures 8 and 9.

[0056] In other implementations, the one or more second states comprises a plurality of second states or a continuum of second states. Such a range of second states may be achieved, for example, by switching the beam modifying element 40 through the second states to progressively suppress an increasing proportion of the portion of the laser beam 14 as the laser focus approaches the second face 38 during processing of the proximal portion 34. The actuation system 42 may be configured, for example, to provide a plurality of second states by progressively inserting the beam modifying element 40 into the path of the laser beam 14 by a progressively increasing amount (e.g., to the left relative to the lens 20 in the orientation shown in Figures 4-6).

[0057] The switching of the beam modifying element 40 from the first state to the second state or second states may be achieved at least partly by moving the beam modifying element 40 relative to the laser beam 14 (e.g., in a direction perpendicular to a principal axis of the laser beam 14 and / or of the lens 20).

[0058] In some implementations, the beam modifying element 40 comprises a spatial light modulator (SLM) such as a micro-mirror array. The switching of the beam modifying element 40 in this case may comprise controlling the SLM to selectively prevent propagation of a portion of a cross-section of the laser beam 14 through the SLM. For example, functionality similar to that described with reference to Figures 4-9 could be achieved by controlling the SLM to switch from a configuration in which pixels of the SLM are substantially all transmissive (corresponding to the cross-section shown in Figure 7) to a configuration in which half of the pixels of the SLM are configured to block transmission through the SLM, to achieve the cross-sections of Figures 8 and 9.

[0059] In some implementations, the beam modifying element 40 may be configured to introduce phase distortion into the portion of the laser beam 14 that is suppressed. Introducing phase distortion disrupts constructive interference between different parts of the laser beam 14 and thereby has a similar effect to blocking portions of the laser beam 14.

[0060] In the example of Figures 4-9, the beam modifying element 40 is positioned upbeam of the lens 20 but this is not essential. In other configurations the beam modifying element 40 is positioned downbeam of the lens. In some configurations, as exemplified in Figure 19, the beam modifying element 40 may be connected to the sample 18. The beam modifying element 40 may be detachably connected to the sample 18. The beam modifying element 40 may comprise a face having a substantially planar portion 41. The beam modifying element 40 may be connected to the sample 18 such that the planar portion 41 of the face of the beam modifying element 40 is coplanar with the first face 28 of the sample 18.

[0061] In the examples of Figures 4-9, the laser beam 14 is controlled such that a continuously modified region is formed in the sample 18 extending along the processing trajectory 26 from the proximal portion 34 to the distal portion 36. In some implementations, the method may comprise controlling the laser beam 14 to form a sequence of spatially separated modified regions 26a along the first processing trajectory 26 in the sample 18. These separated modified regions 26a may be formed in addition to the continuously modified region, or only the spatially separated modified regions 26a may be formed. The spatially separated modified regions 26a are discrete regions of structural modification within the sample 18. The laser beam 14 may be controlled in multiple discrete pulses or may be gated to form the discrete regions of structural modification within the sample 18. The discrete regions of structural modification (which may be volume pixels or voxels) may cause diffraction and / or scatter of an incident light field as per a design (as described in Barre et al. Advanced Photonics Nexus 2, 036006 (2023)) to give a different optical output field.

[0062] Figures 10-12 schematically depict processing of a sample 16 at three different time points along a processing trajectory 26 in which the laser beam 14 is controlled to form a sequence of spatially separated modified regions 26a. Implementations of this class may otherwise have some or all of the features of the examples described above.

[0063] Figure 10 depicts processing at a first time point when the laser beam 14 is focused within the distal portion 36 of the sample 18 and controlled to form a spatially separated modified region 26a along the processing trajectory 26. The modified region 26a may form one or more discrete regions of structural modification, such as volume pixels or voxels.

[0064] Figure 11 depicts processing at a second time point when the laser beam 14 is being controlled such that the sample is not being modified between the spatially separated modified regions 26a (understood in this context to include the regions of the processing trajectory 26 which will become the modified regions 26a once processed) of the sample 18. The broken lines illustrate the position of the laser focus 30 within the sample as it moves relative to the sample along the processing trajectory 26 while the laser beam is not modifying the sample.

[0065] Figure 12 depicts processing at a third time point when the laser focus 30 is within the proximal portion 34 and closer to the second face 38 than to the distal portion 36. In the example depicted by Figure 12, the sample 18 is modified at three discrete portions 26a of the processing trajectory 26. In the case that the sample 18 is modified in a plurality of discrete portions 26a of the processing trajectory 26, the laser beam is interacted with or adjusted during processing of the proximal portion 34 to reduce or prevent impingement of the laser beam 14 onto the second face 38 during the processing of the proximal portion 34. The interaction or adjustment may take any of the forms described herein.

[0066] In an implementation where the sample 18 is modified in a plurality of discrete portions 26a of the processing trajectory 26, the relative movement of the laser focus 30 and the sample 18 may be moved in the range of speeds previously described. The relative movement may be continuous, or there may be a reduced speed of movement or no relative movement between the laser focus 30 and the sample 18 when the sample 18 is being modified in the discrete portions 26a. The spatially separated modified regions 26a may have dimensions ranging from 0.5 / / m x 0.5 / / m x 0.5 / / m through to dimensions ranging from 2 m x 10 / / m x 10 / / m. Separations between the modified regions 26a may be between l / / m and 100 / / m, preferably l O m, and the refractive index contrast may be between 0.1% to 5%, and preferably approximately 1%.

[0067] In the examples described above, the laser beam 14 is interacted with or otherwise adjusted to reduce or prevent impingement of the laser beam 14 onto the second face 38 during the processing of the proximal portion 34. Figures 13-15 depict a first modification to the above examples in which the laser beam is interacted with or adjusted during the processing of the edge distal portion to reduce or prevent impingement of the laser beam onto a third face 39 of the sample 18. In this example, the distal portion of the processing trajectory 26 consists of an edge distal portion 36a adjacent to the third face 39 of the sample 18, and a central distal portion 36b between the edge distal portion 36a and the proximal portion 34.

[0068] The third face 39 is a face that is non-parallel to the first face 28. The third face 39 may, for example, comprise a peripheral edge of the sample 18. The third face 39 may be substantially planar, at least locally (e.g., in a region that would be traversed by an extrapolation of the processing trajectory 26 through the third face 39). The third face 39 may be substantially perpendicular to the first face 28, at least locally (e.g., in a region that would be traversed by an extrapolation of the processing trajectory 26 through the third face 39). The third face 39 may be substantially parallel or perpendicular to the second face 38.

[0069] Figure 13 depicts processing at a first time point when the laser focus 30 is within the edge distal portion 36a. Figure 14 depicts processing at a first time point when the laser focus 30 is within the central distal portion 36b, relatively far from either of the edge distal portion 36a or the proximal portion 34. Figure 15 depicts processing at a third time point when the laser focus 30 is within the proximal portion 34.

[0070] In this example, the laser beam 14 is interacted with or adjusted during the processing of the edge distal portion 36a to reduce or prevent impingement of the laser beam 14 onto the third face 39 during the processing of the edge distal portion 36a. The processing of the edge distal portion 36a in this example may be the same in some or all respects as the processing of the proximal portion 34 in the examples above. In this example, the beam modifying element 40 is configured to be switched between one or more first states, one or more second states, and a third state. Each first state is such that the beam modifying element 40 suppresses at least a part of a first portion of the laser beam 14, and each second state is such that the beam modifying element 14 suppresses at least a part of a second portion of the laser beam 14. The third state is such that the beam modifying element 40 does not suppress any portion of the laser beam 14. Figure 13 shows the beam modifying element 40 in a first state such that the beam modifying element 40 suppresses at least part of a first portion of the laser beam 14 during the processing of the edge distal portion 36a. Figure 14 shows the beam modifying element 40 in the third state during the processing of the central distal portion 36b, such that the laser beam 14 is not suppressed. Figure 15 shows the beam modifying element in a second state such that the beam modifying element 40 suppresses at least part of a second portion of the laser beam 14 during the processing of the processing of the edge distal portion 36a.

[0071] In this example, there is only a single first state and single second state in which the beam is suppressed respectively, however the beam modifying element 40 may be configured to have more than one first and second states for suppressing the laser beam 14, as has been described previously. The switching of the beam modifying element 40 between each of the states may be performed in any manner described above.

[0072] A first portion of the laser beam 14 suppressed during the processing of the proximal portion 34 may be different to a second portion of the laser beam that is suppressed during the processing of the edge distal portion 36a, as depicted in Figures 13 and 15. In some implementations, the first and second portions are non-overlapping. The relationship between the first and second portions of the laser beam 14 that are suppressed will typically depend on the spatial relationship between the second face 38 and third face 39 of the sample.

[0073] In this example, the use of the beam modifying element 40 is described. In some implementations, the beam modifying element 40 may take the form of a single unit. In some implementations, the beam modifying element 40 may take the form of multiple subunits, which may be spatially separated from each other. For example, a first sub-unit may suppress the first portion of the laser beam 14 and a second sub-unit may suppress the second portion of the laser beam 14. Multiple sub-units of the beam modifying element 40 may be controlled by the same actuator 42 or by independent actuators 42.

[0074] Figures 16 to 18 depict a second modification to the above examples in which the laser beam 14 is interacted with or adjusted to prevent impingement of the laser beam onto a third face 39 of the sample 18 during the processing of the edge distal portion 36a.

[0075] In contrast to the examples of Figures 13-15, in this example the beam modifying element 40 is only configured to be switched between the one or more first states such that the beam modifying element 40 suppresses at least part of a first portion of the laser beam 14 and the one or more second states such that the beam modifying element 40 suppresses at least part of a second portion of the laser beam 14. Figure 16 depicts the beam modifying element 40 in a first state during the processing of the edge distal portion 36a. Figure 17 depicts the beam modifying element 40 maintained in the first state such that the laser beam 14 remains suppressed during the processing of the central distal portion 36b. Figure 18 depicts the beam modifying element 40 having been switched to a second state during the processing of the processing of the proximal portion 34. Alternatively, the beam modifying element may be switched into the second state for the processing of both the central distal portion 36b and the proximal portion 34. In such implementations, the beam modifying element 40 only need be switched between states once for the whole modification operation, which may simplify the manufacture of modified regions of the sample.

[0076] In the examples described above, the laser beam 14 is interacted with or otherwise adjusted to reduce or prevent impingement of the laser beam 14 onto the second face 38 by suppressing a contribution to the laser focus 30 from a portion of the laser beam 14 (e.g., by suppressing or blocking a semi-cone, or near semi-cone, of the laser beam 14). Figure 20 depicts an alternative or additional approach in which the reduction or prevention of impingement of the laser beam 14 onto the second face 38 is at least partly achieved by changing an average direction of propagation of the laser beam 14 towards the sample 18. In the configuration shown, this is achieved by varying where the laser beam 14 impinges on the lens 20, but a range of optical configurations could be envisaged to achieve similar effects. In the configuration shown, the average direction of propagation is changed by provided a lateral relative translation between the lens 20 focusing the laser beam 14 onto the sample 18 and the laser beam 14 incident on the lens 20.

[0077] The changing of the average direction of propagation of the laser beam 14 may comprise, for example, changing from an average direction of propagation that is substantially perpendicular to the first face 28 of the sample 18 to an average direction of propagation that is oblique relative to the first face 28 of the sample 18, typically angled away from the second face 38 relative to a normal to the first face 28. The perpendicular propagation may be used when processing a distal portion 36 of the processing trajectory 26 (see Figures 3-19). The oblique propagation may be used for example when processing a proximal portion 34 of the processing trajectory 26 (see Figures 3-19).

[0078] In the example shown, broken lines schematically depict impingement of a laser beam 14A onto the lens 20 that is coaxially aligned with the lens 20. The resulting cone of focussed laser light has a principal axis, representing an average direction of propagation, that is aligned with the lens 20 axis and perpendicular to the first face 28 of the sample 18, similar to the configurations described above with reference to Figures 3-19. This configuration would be suitable for processing a distal portion 36 of the processing trajectory 20.

[0079] Solid lines schematically depict impingement of a laser beam 14B onto the lens 20 along an axis that is laterally displaced to the left (arrow 44) relative to axis of the lens 20. Impingement of the laser beam 14B onto the lens 20 in this manner may be referred to as off-axis impingement. In the example shown, the axis of the laser beam 14B upbeam of the lens 20 is parallel to the axis of the lens 20 but this is not essential. The off-axis impingement onto the lens causes the focussed laser light to have an average direction of propagation that is aligned obliquely relative of the axis of the lens 20. As shown in Figure 20, in contrast to the situation for laser beam 14A, which is seen to impinge onto the second face 28, the oblique alignment of the focussed laser light of the laser beam 14B prevents impingement of laser light from the laser beam 14B onto the second face 38. This configuration would thus be suitable for processing a proximal portion 34 of the processing trajectory 26. In contrast to the approaches described with reference to Figures 4-19 where a portion of the laser beam 14 was suppressed, the approach of Figure 20 may reduce an amount by which a power of the laser beam 14 needs to be increased to compensate for the measures taken to reduce or avoid impingement onto the second face 38. Regardless of the approach taken, a power of the laser beam 14 may be increased during the interaction with or adjustment of the laser beam 14 to reduce or prevent impingement of the laser beam 14 onto the second face 38. The increase in power may at least partially compensate for the interaction or adjustment. The power may be increased to a level that ensures that a desired modification of material in the processing trajectory continues to take place at an appropriate rate. The adjustment may comprise increasing the power of the laser beam by a factor of between 2 and 6, optionally substantially 4. Typically, a range of laser powers may be used with an optimal value being selected based on the particular material characteristics of the sample 18, the processing that it is desired to perform, and details of optics used to focus the laser beam 14 onto the processing trajectory 26. Typically, a laser power would be in the range of about lOmW to lOOmW, such as around 50mW, during processing of a distal region 36 (i.e., without any suppression of a portion of the laser beam to reduce or avoid impingement on the second face 38). During processing of the proximal portion 34, where a portion of the laser beam is suppressed, the laser power may be increased by a factor as mentioned above. In one implementation, the laser power is increased to around 200mW during processing of the proximal portion 34.

[0080] Figure 21 depicts cross sections of waveguides written at 500 micron depth below a first face 28 of a sample 18 imaged in a transmission light microscope. The images are end-on images of the waveguides, looking along longitudinal axes of the waveguides.

[0081] The portion of the main image indicated by arrow 52 corresponds to the position of a waveguide written using traditional techniques. The waveguide formed in this manner “fades out” (becomes progressively less well defined) towards the edge of the sample 18, resulting in a blurred image. The bottom left inset depicts a waveguide coupled mode 53 corresponding to the waveguide indicated by arrow 52. The mode 53 is relatively blurred, indicated high losses.

[0082] The portion of the main image indicated by arrow 54 corresponds to the position of a waveguide written using a method of the present disclosure, which allows the waveguide to continue to be formed effectively even as the laser focus 30 gets very close to the edge of the sample 18 or even reaches the edge of the sample 18. The waveguide indicated by arrow 54 in the main image is thus seen much more sharply than the waveguide indicated by arrow 52. The waveguide of arrow 54 is well defined closer to the surface than the waveguide of arrow 52. The bottom right inset depicts a waveguide coupled mode 55 corresponding to the waveguide indicated by arrow 54. The mode 55 is more concentrated than mode 53, indicated lower losses.

[0083] Figure 22 shows simulations for predicting a desired increase in laser power to compensate for suppression of a portion of the laser beam 14 to avoid impingement of the laser beam on the second face 38 as discussed above. The simulations model impingement of a focused laser beam 14 along a Z direction of a Cartesian coordinate system towards a laser focus 30 within a sample 18. A first face 28 of the sample 18 is parallel to the X-Y plane. In Figure 22, the upper row of three images depict simulated spatial variation of laser light intensity in a Z-X plane. The lower row of three images depict simulated spatial variation of laser light intensity in an X-Y plane. The left-most column represents simulations for the case where a leftmost semi-circularly shaped half of a cross-section of the laser beam 14 is blocked from reaching the sample 18 (as depicted schematically at the top left of Figure 22). The right-most column represents simulations for the case where a rightmost semi-circularly shaped half of a cross-section of the laser beam 14 is blocked from reaching the sample 18 (as depicted schematically at the top right of Figure 22). The left- and rightmost columns thus represent simulated intensities for configurations similar to those of Figures 5, 6, 8 and 9, in which a semi-cone of the laser beam 14 is blocked by a beam modifying device 40. The central column represents simulations for the case where no portion of the laser beam 14 is blocked. The central column thus represents simulated intensities for a configuration similar to that of Figures 4 and 7. The simulations show that in this particular configuration the intensity at the processing trajectory 26 is reduced by a factor of 4 when half of the cross-section of the laser beam 14 is blocked (leftmost and rightmost columns) relative to when the laser beam 14 is unblocked (central column). In this configuration it would therefore be effective to compensate for blocking of the portion of the laser beam 14 by increasing the power of the laser by a factor of about 4.

[0084] The examples above describe the modification of a sample along a single processing trajectory 26. However, the methods described herein are also applicable to modifying a sample along multiple processing trajectories 26 simultaneously. In some implementations, the sample 18 may be modified along one or more further processing trajectories 26 in the sample by providing a respective one or more further laser beams 14, where each further processing trajectory 26 comprises a respective proximal portion 34 and distal portion 36 defined similarly to the single processing trajectory 26 described above. The further laser 14 beams may be provided by splitting a source laser beam. The one or more further laser beams 14 may be focused through the first face 28 of the sample 18 to respective one or more further laser foci 30 in the sample 18 and relative movement provided between the laser foci 30 and the sample 18 to move the laser foci 30 along respective one or more further processing trajectories 26. The relative movement may be performed in any manner previously described. The one or more further laser beams 14 may be interacted with or adjusted during processing of the respective proximal portions 34 to reduce or prevent impingement of each respective further laser beam 14 onto the second face 38 during the processing of the respective proximal portions 34. The interaction or adjustment may take any form previously described. The interaction or adjustment may be performed in the same manner for each of the laser beams 14 used to modify the sample, or in a different manner between some or all of the laser beams 14. Each further processing trajectory 26 may be substantially parallel to the (first) processing trajectory.

[0085] In some implementations, the apparatus 10 may be configured to implement a laser processing method comprising using the laser beam 14 to modify the sample 18 by focusing the laser beam 14 through a first face 28 of the sample 18 to a laser focus 30 in the sample 18. The sample comprises a proximal portion and a distal portion, the proximal portion being nearer to a second face 38 of the sample 18 than the distal portion. The method comprises interacting with or adjusting the laser beam 14 when the laser is focused to a laser focus 30 within the proximal portion of the sample to reduce or prevent impingement of the laser beam 14 onto the second face 38. The interaction or adjustment comprises suppressing a contribution to the laser focus 30 from a portion of the laser beam 14. Such implementations may be used to form one or more modified regions in the proximal region of sample 18. The modified region may extend between the proximal region of the sample 18 and the distal region of the sample 18, or the modified region may only be formed in the proximal region of the sample. For example, a single discrete region of structural modification may be formed in the proximal portion of the sample, such as a volume pixel or voxel. Such regions of structural modification may have dimensions as previously described. In some implementations, contributions to the laser focus 30 from a portion of the laser beam 14 are not suppressed when the laser beam 14 is focused to a laser focus 30 in the distal portion 36 of the sample. Relative movement may be provided between the laser focus 30 and the sample 18 to move the laser focus 30 within the sample during the processing of the sample 18, or there may be no relative movement between the laser focus 30 and the sample 18 during the processing. The suppression of a contribution of the laser focus 30 is not limited and may take any of the forms previously described.

[0086] Figures 23 to 29 show the relative performance of waveguides formed using traditional methods with no edge correction, and those formed using edge correction according to embodiments of the disclosure as has previously been described. Figures 24 and 26 show waveguide modes imaged from the edge of the sample (corresponding to the second face as described above) in fused silica and EAGLE 2000 samples, where the waveguides were formed with no edge correction (reduction in impingement on the second face). Figures 23 and 25 show corresponding measurements of the dimensions of the waveguide mode fields, and also waveguide mode fields where the waveguides were formed with edge correction according to embodiments of the disclosure. The graphs of Figures 27 and 28 show that with no edge correction, the dimensions of the mode field increase with the waveguide depth in the sample. When the edge correction is applied, the dimension of the mode field is much more consistent, and closer to the dimension of an optical fibre.

[0087] Figure 29 demonstrates transmission coefficients between waveguides formed in the samples and an optical fibre. The data shows that mode size with edge correction according to embodiments of the disclosure allows consistent mode size at different depths despite edge effects, giving lower loss coupling to optical fibre than traditional methods.

[0088] The following numbered clauses define embodiments of the disclosure.

[0089] 1. A laser processing method, comprising: using a laser beam to modify a sample along a processing trajectory in the sample by focusing the laser beam through a first face of the sample to a laser focus in the sample and providing relative movement between the laser focus and the sample to move the laser focus along the processing trajectory, wherein: the processing trajectory comprises a proximal portion and a distal portion, the proximal portion being nearer to a second face of the sample than the distal portion; and the method comprises interacting with or adjusting the laser beam during processing of the proximal portion to reduce or prevent impingement of the laser beam onto the second face during the processing of the proximal portion.

[0090] 2. The method of clause 1, wherein the modification of the sample along the first processing trajectory comprises: controlling the laser beam to form a continuously modified region extending along the first processing trajectory from the proximal portion to the distal portion; and / or controlling the laser beam to form a sequence of spatially separated modified regions along the first processing trajectory.

[0091] 3. The method of clause 1 or 2, further comprising increasing a power of the laser beam during the interaction with or adjustment of the laser beam to at least partially compensate for the interaction or adjustment.

[0092] 4. The method of any of clauses 1 to 3, wherein the interaction or adjustment comprises suppressing a contribution to the laser focus from a portion of the laser beam.

[0093] 5. The method of clause 4, wherein the portion of the laser beam is suppressed using a beam modifying element in a path of the laser beam.

[0094] 6. The method of clause 5, wherein the beam modifying element is configured to block the portion of the laser beam.

[0095] 7. The method of clause 6, wherein the beam modifying element is configured to introduce phase distortion into the portion of the laser beam.

[0096] 8. The method of any of clauses 5-7, wherein the laser beam is focused onto the sample by a lens and the beam modifying element is downbeam of the lens.

[0097] 9. The method of any of clauses 5-8, wherein the beam modifying element is connected to the sample.

[0098] 10. The method of any of clauses 5-7, wherein the laser beam is focused onto the sample by a lens and the beam modifying element is upbeam of the lens.

[0099] 11. The method of any of clauses 5-10, wherein: the beam modifying element is configured to be switched between a first state and one or more second states; the first state is such that the beam modifying element does not suppress the portion of the laser beam; and each second state is such that the beam modifying element does suppress at least part of the portion of the laser beam.

[0100] 12. The method of clause 11, wherein the beam modifying element is maintained in the first state during processing of the distal portion and is switched into one or more of the second states during processing of the proximal portion.

[0101] 13. The method of clause 12, wherein the one or more second states comprises a single second state and the single second state is maintained during all of the processing of the proximal portion.

[0102] 14. The method of clause 13, wherein the one or more second states comprises a plurality of second states or a continuum of second states and the beam modifying element is switched through the second states to progressively suppress an increasing proportion of the portion of the laser beam as the laser focus approaches the second face during processing of the proximal portion.

[0103] 15. The method of any of clauses 11-14, wherein the switching is performed at least partly by moving the beam modifying element relative to the laser beam.

[0104] 16. The method of any of clauses 11-15, wherein the beam modifying element comprises a spatial light modulator and the switching is performed at least partly by changing a state of the spatial light modulator.

[0105] 17. The method of any of clauses 4-16, wherein the suppressed portion of the laser beam comprises at least 20% of a cross-section of the laser beam, optionally substantially half of the cross-section of the laser beam.

[0106] 18. The method of clause 17, wherein the suppressed portion of the laser beam substantially comprises a semi-cone of the laser beam between a lens and the sample.

[0107] 19. The method of any preceding clause, wherein a power of the laser beam during the interaction with or adjustment of the laser beam is increased by a factor of between 2 and 6, optionally substantially 4.

[0108] 20. The method of any preceding clause, wherein the interaction with or adjustment of the laser beam comprises changing an average direction of propagation of the laser beam towards the sample. 21. The method of clause 20, wherein the average direction of propagation is changed by provided a lateral relative translation between a lens focusing the laser beam onto the sample and the laser beam incident on the lens.

[0109] 22. The method of any preceding clause, wherein the interaction with or adjustment of the laser beam is such that a fluence of the laser beam impinging onto the second face during the processing of the proximal portion is reduced by at least 10%.

[0110] 23. The method of any preceding clause, further comprising: modifying the sample along one or more further processing trajectories in the sample by providing a respective one or more further laser beams, optionally by splitting a source laser beam, each further processing trajectory comprising a respective proximal portion and distal portion; focusing the one or more further laser beams through the first face of the sample to respective one or more further laser foci in the sample; providing relative movement between the laser foci and the sample to move the laser foci along respective one or more further processing trajectories; and interacting with or adjusting the one or more further laser beams during processing of the respective proximal portions to reduce or prevent impingement of each respective further laser beam onto the second face during the processing of the respective proximal portions.

[0111] 24. The method of clause 23, wherein each further processing trajectories is substantially parallel to the processing trajectory.

[0112] 25. The method of any of clauses 5-10, wherein: the distal portion consists of an edge distal portion adjacent to a third face of the sample and a central distal portion between the edge distal portion and the proximal portion; the method comprises interacting with or adjusting the laser beam during processing of the edge distal portion to reduce or prevent impingement of the laser beam onto the third face during the processing of the edge distal portion, wherein: the beam modifying element is configured to be switched from one or more first states to one or more second states; each first state is such that the beam modifying element suppresses at least a part of a first portion of the laser beam; each second state is such that the beam modifying element suppresses at least a part of a second portion of the laser beam.

[0113] 26. The method of clause 25, wherein the beam modifying element is in the one or more first states during processing of the edge distal portion and is in the one or more of second states during processing of the proximal portion.

[0114] 27. The method of clause 26, wherein the beam modifying element is in the one or more of first states during processing central distal portion.

[0115] 28. The method of clause 26 or 27, wherein: the beam modifying element is further configured to be switched into a third state, wherein the third state is such that the beam modifying element does not suppress any portion of the laser beam; and the beam modifying element is in the third state during the processing of the central distal portion.

[0116] 29. The method of any of clauses 25 to 28, wherein the first portion and the second portion of the laser beam are different, optionally non-overlapping.

[0117] 30. A laser processing method, comprising: using a laser beam to modify a sample by focusing the laser beam through a first face of the sample to a laser focus in the sample, wherein the sample comprises a proximal portion and a distal portion, the proximal portion being nearer to a second face of the sample than the distal portion; and the method comprises suppressing a contribution to the laser focus from a portion of the laser beam when the laser is focused to a laser focus within the proximal portion to reduce or prevent impingement of the laser beam onto the second face.

[0118] 31. The method of clause 30, further comprising modifying the sample by focusing the laser beam through a first face of the sample to a laser focus in the sample in the distal portion of the sample, wherein no contributions to the laser focus from a portion of the laser beam are suppressed when the laser beam is focused to a laser focus in the distal portion of the sample.

[0119] 32. A laser processing apparatus, comprising: a laser configured to generate a laser beam; a sample support configured to support a sample; a lens configured to focus the laser beam onto the sample; a beam adjuster configured to adjust a configuration of the laser beam; and a control system configured to control the laser, the sample support, and the beam adjuster, to: modify a sample along a processing trajectory in the sample by focusing the laser beam through a first face of the sample to a laser focus in the sample and provide relative movement between the laser focus and the sample to move the laser focus along the processing trajectory, wherein: the processing trajectory comprises a proximal portion and a distal portion, the proximal portion being nearer to a second face of the sample than the distal portion; and the control system is configured to control the laser and / or the beam adjuster to interact with or adjust the laser beam during processing of the proximal portion to reduce or prevent impingement of the laser beam onto the second face during the processing of the proximal portion.

[0120] 33. The apparatus of clause 32, wherein the control system is configured to increase a power of the laser beam during the interaction with or adjustment of the laser beam to at least partially compensate for the interaction or adjustment.

[0121] 34. The apparatus of clause 32 or 33, wherein the interaction or adjustment comprises suppressing a contribution to the laser focus from a portion of the laser beam.

[0122] 35. The apparatus of clause 34, wherein the portion of the laser beam is suppressed using a beam modifying element in a path of the laser beam.

[0123] 36. The apparatus of clause 35, wherein the beam modifying element is configured to block the portion of the laser beam.

[0124] 37. The apparatus of clause 35, wherein the beam modifying element is configured to introduce phase distortion into the portion of the laser beam.

[0125] 38. The apparatus of any of clauses 35-37, wherein the beam modifying element is downbeam of the lens.

[0126] 39. The apparatus of any of clauses 35-38, wherein the beam modifying element is connected to the sample.

[0127] 40. The apparatus of any of clauses 35-37, wherein the beam modifying element is upbeam of the lens.

[0128] 41. The apparatus of any of clauses 35-40, wherein: the beam modifying element is configured to be switched from a first state to one or more second states; the first state is such that the beam modifying element does not suppress the portion of the laser beam; and each second state is such that the beam modifying element does suppress at least part of the portion of the laser beam.

[0129] 42. The apparatus of clause 41, wherein the control system is configured to maintain the beam modifying element in the first state during processing of the distal portion and to switch the beam modifying element into one or more of the second states during processing of the proximal portion.

[0130] 43. The apparatus of clause 42, wherein the one or more second states comprises a single second state and the single second state is maintained during all of the processing of the proximal portion.

[0131] 44. The apparatus of clause 43, wherein the one or more second states comprises a plurality of second states or a continuum of second states and the control system is configured to switch the beam modifying element through the second states to progressively suppress an increasing proportion of the portion of the laser beam as the laser focus approaches the second face during processing of the proximal portion.

[0132] 45. The apparatus of any of clauses 41-44, wherein the control system is configured to perform the switching at least partly by moving the beam modifying element relative to the laser beam.

[0133] 46. The apparatus of any of clauses 41-45, wherein the beam modifying element comprises a spatial light modulator and the control system is configured to perform the switching at least partly by changing a state of the spatial light modulator.

[0134] 47. The apparatus of any of clauses 44-46, wherein the suppressed portion of the laser beam comprises at least 20% of a cross-section of the laser beam, optionally substantially half of the cross-section of the laser beam.

[0135] 48. The apparatus of clause 47, wherein the suppressed portion of the laser beam substantially comprises a semi-cone of the laser beam between the lens and the sample. 49. The apparatus of any of clauses 32-48, wherein a power of the laser beam during the interaction with or adjustment of the laser beam is increased by a factor of between 2 and 6, optionally substantially 4.

[0136] 50. The apparatus of any of clauses 32-49, wherein the interaction with or adjustment of the laser beam comprises changing an average direction of propagation of the laser beam towards the sample.

[0137] 51. The apparatus of clause 50, wherein control system is configured to change the average direction of propagation by provided a lateral relative translation between the lens focusing the laser beam onto the sample and the laser beam incident on the lens.

[0138] Cross reference to related applications

[0139] This application claims priority from GB 2403210.4_filed on 5 March 2024, the contents of which are hereby incorporated by reference.

Claims

CLAIMS1. A laser processing method, comprising: using a laser beam to modify a sample along a processing trajectory in the sample by focusing the laser beam through a first face of the sample to a laser focus in the sample and providing relative movement between the laser focus and the sample to move the laser focus along the processing trajectory, wherein: the processing trajectory comprises a proximal portion and a distal portion, the proximal portion being nearer to a second face of the sample than the distal portion; and the method comprises interacting with or adjusting the laser beam during processing of the proximal portion to reduce or prevent impingement of the laser beam onto the second face during the processing of the proximal portion.

2. The method of claim 1, wherein the modification of the sample along the first processing trajectory comprises: controlling the laser beam to form a continuously modified region extending along the first processing trajectory from the proximal portion to the distal portion; and / or controlling the laser beam to form a sequence of spatially separated modified regions along the first processing trajectory.

3. The method of claim 1 or 2, further comprising increasing a power of the laser beam during the interaction with or adjustment of the laser beam to at least partially compensate for the interaction or adjustment.

4. The method of any of claims 1-3, wherein the interaction or adjustment comprises suppressing a contribution to the laser focus from a portion of the laser beam.

5. The method of claim 4, wherein the portion of the laser beam is suppressed using a beam modifying element in a path of the laser beam.

6. The method of claim 5, wherein the beam modifying element is configured to blockthe portion of the laser beam.

7. The method of claim 5, wherein the beam modifying element is configured to introduce phase distortion into the portion of the laser beam.

8. The method of any of claims 5-7, wherein the laser beam is focused onto the sample by a lens and the beam modifying element is downbeam of the lens.

9. The method of any of claims 5-8, wherein the beam modifying element is connected to the sample.

10. The method of any of claims 5-7, wherein the laser beam is focused onto the sample by a lens and the beam modifying element is upbeam of the lens.

11. The method of any of claims 5-10, wherein: the beam modifying element is configured to be switched between a first state and one or more second states; the first state is such that the beam modifying element does not suppress the portion of the laser beam; and each second state is such that the beam modifying element does suppress at least part of the portion of the laser beam.

12. The method of claim 11, wherein the beam modifying element is maintained in the first state during processing of the distal portion and is switched into one or more of the second states during processing of the proximal portion.

13. The method of claim 12, wherein the one or more second states comprises a single second state and the single second state is maintained during all of the processing of the proximal portion.

14. The method of claim 12, wherein the one or more second states comprises aplurality of second states or a continuum of second states and the beam modifying element is switched through the second states to progressively suppress an increasing proportion of the portion of the laser beam as the laser focus approaches the second face during processing of the proximal portion.

15. The method of any of claims 11-14, wherein the switching is performed at least partly by moving the beam modifying element relative to the laser beam.

16. The method of any of claims 11-15, wherein the beam modifying element comprises a spatial light modulator and the switching is performed at least partly by changing a state of the spatial light modulator.

17. The method of any of claims 4-16, wherein the suppressed portion of the laser beam comprises at least 20% of a cross-section of the laser beam, optionally substantially half of the cross-section of the laser beam.

18. The method of claim 17, wherein the suppressed portion of the laser beam substantially comprises a semi-cone of the laser beam between a lens and the sample.

19. The method of any preceding claim, wherein a power of the laser beam during the interaction with or adjustment of the laser beam is increased by a factor of between 2 and 6, optionally substantially 4.

20. The method of any preceding claim, wherein the interaction with or adjustment of the laser beam comprises changing an average direction of propagation of the laser beam towards the sample.

21. The method of claim 20, wherein the average direction of propagation is changed by provided a lateral relative translation between a lens focusing the laser beam onto the sample and the laser beam incident on the lens.

22. The method of any preceding claim, wherein the interaction with or adjustment of the laser beam is such that a fluence of the laser beam impinging onto the second face during the processing of the proximal portion is reduced by at least 10%.

23. The method of any preceding claim, further comprising: modifying the sample along one or more further processing trajectories in the sample by providing a respective one or more further laser beams, optionally by splitting a source laser beam, each further processing trajectory comprising a respective proximal portion and distal portion; focusing the one or more further laser beams through the first face of the sample to respective one or more further laser foci in the sample; providing relative movement between the laser foci and the sample to move the laser foci along respective one or more further processing trajectories; and interacting with or adjusting the one or more further laser beams during processing of the respective proximal portions to reduce or prevent impingement of each respective further laser beam onto the second face during the processing of the respective proximal portions.

24. The method of claim 23, wherein each further processing trajectories is substantially parallel to the processing trajectory.

25. The method of any of claims 5-10, wherein: the distal portion consists of an edge distal portion adjacent to a third face of the sample and a central distal portion between the edge distal portion and the proximal portion; the method comprises interacting with or adjusting the laser beam during processing of the edge distal portion to reduce or prevent impingement of the laser beam onto the third face during the processing of the edge distal portion, wherein: the beam modifying element is configured to be switched from one or more first states to one or more second states; each first state is such that the beam modifying element suppresses at least a part ofa first portion of the laser beam; each second state is such that the beam modifying element suppresses at least a part of a second portion of the laser beam.

26. The method of claim 25, wherein the beam modifying element is in the one or more first states during processing of the edge distal portion and is in the one or more of second states during processing of the proximal portion.

27. The method of claim 26, wherein the beam modifying element is in the one or more of first states during processing central distal portion.

28. The method of claim 26 or 27, wherein: the beam modifying element is further configured to be switched into a third state, wherein the third state is such that the beam modifying element does not suppress any portion of the laser beam; and the beam modifying element is in the third state during the processing of the central distal portion.

29. The method of any of claims 25 to 28, wherein the first portion and the second portion of the laser beam are different, optionally non-overlapping.

30. A laser processing method, comprising: using a laser beam to modify a sample by focusing the laser beam through a first face of the sample to a laser focus in the sample, wherein the sample comprises a proximal portion and a distal portion, the proximal portion being nearer to a second face of the sample than the distal portion; and the method comprises suppressing a contribution to the laser focus from a portion of the laser beam when the laser is focused to a laser focus within the proximal portion to reduce or prevent impingement of the laser beam onto the second face.

31. The method of claim 30, further comprising modifying the sample by focusing thelaser beam through a first face of the sample to a laser focus in the sample in the distal portion of the sample, wherein no contributions to the laser focus from a portion of the laser beam are suppressed when the laser beam is focused to a laser focus in the distal portion of the sample.

32. A laser processing apparatus, comprising: a laser configured to generate a laser beam; a sample support configured to support a sample; a lens configured to focus the laser beam onto the sample; a beam adjuster configured to adjust a configuration of the laser beam; and a control system configured to control the laser, the sample support, and the beam adjuster, to: modify a sample along a processing trajectory in the sample by focusing the laser beam through a first face of the sample to a laser focus in the sample and provide relative movement between the laser focus and the sample to move the laser focus along the processing trajectory, wherein: the processing trajectory comprises a proximal portion and a distal portion, the proximal portion being nearer to a second face of the sample than the distal portion; and the control system is configured to control the laser and / or the beam adjuster to interact with or adjust the laser beam during processing of the proximal portion to reduce or prevent impingement of the laser beam onto the second face during the processing of the proximal portion.

33. The apparatus of claim 32, wherein the control system is configured to increase a power of the laser beam during the interaction with or adjustment of the laser beam to at least partially compensate for the interaction or adjustment.

34. The apparatus of claim 32 or 33, wherein the interaction or adjustment comprises suppressing a contribution to the laser focus from a portion of the laser beam.

35. The apparatus of claim 34, wherein the portion of the laser beam is suppressedusing a beam modifying element in a path of the laser beam.

36. The apparatus of claim 35, wherein the beam modifying element is configured to block the portion of the laser beam.

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