A Plate polarising beam splitter 22 splits an incident laser beam 21 to form a first laser beam 24 and a second laser beam 25. The first laser beam is optically modified using an arcuate reflector 23 so that the first laser beam has a different divergence or convergence from that of the second laser
A Plate polarising beam splitter 22 splits an incident laser beam 21 to form a first laser beam 24 and a second laser beam 25. The first laser beam is optically modified using an arcuate reflector 23 so that the first laser beam has a different divergence or convergence from that of the second laser beam. The first laser beam 24 is focussed at a first focus 27 on an optical axis of a focussing lens 26 and the second laser beam is focussed at a second focus 28 on the optical axis for machining a workpiece. The apparatus is suitable for machining with the laser beams steered by a galvanometer scanner.
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The invention claimed is: 1. A laser machining apparatus comprising a plate polarising beam splitter for splitting an incident polarised laser beam to form a first laser beam and a second laser beam; optical beam modifying optics comprising an arcuate light reflecting device for providing the first
The invention claimed is: 1. A laser machining apparatus comprising a plate polarising beam splitter for splitting an incident polarised laser beam to form a first laser beam and a second laser beam; optical beam modifying optics comprising an arcuate light reflecting device for providing the first laser beam with a different divergence or convergence from that of the second laser beam; focusing optics for focusing the first laser beam at a first focus on an optical axis of the focusing optics and for focusing the second laser beam at a second focus on the optical axis, such that the first focus and the second focus fall at different locations on the optical axis; and a galvanometer for scanning the first laser beam and the second laser beam across a workpiece to machine the workpiece. 2. A laser machining apparatus as claimed in claim 1, wherein the arcuate light reflecting device comprises a convex mirror. 3. A laser machining apparatus as claimed in claim 1, wherein a distance between the first focus and the second focus is selectable by selecting a radius of curvature of the arcuate light reflecting device. 4. A laser machining apparatus as claimed in claim 1, wherein a distance between the first focus and the second focus is between millimeters and tenths of microns. 5. A laser machining apparatus as claimed in claim 1, further comprising a laser beam generator for generating the incident polarised laser beam. 6. A laser machining apparatus as claimed in claim 1, wherein the plate polarising beam splitter comprises a polarisation dependent layer for substantially reflecting the first beam with a first polarisation component and substantially transmitting the second beam with a second polarisation component. 7. A laser machining apparatus as claimed in claim 1, wherein the incident polarised laser beam is substantially collimated. 8. A laser machining apparatus as claimed in claim 1, wherein the first laser beam is substantially collimated and the second laser beam is divergent after modification by the optical beam modifying optics. 9. A laser machining apparatus as claimed in claim 1, wherein the incident polarised laser beam is pulsed. 10. A laser machining apparatus as claimed in claim 1, wherein the laser machining apparatus further comprises a translation table for moving the workpiece with respect to the first laser beam and the second laser beam. 11. A laser machining apparatus as claimed in claim 1, wherein the first laser beam and the second laser beam interfere to form interference fringes and the apparatus further comprises imaging optics and an associated controller for using an image of the interference fringes to align the first and second foci on an optical axis of a scanning lens associated with the galvanometer. 12. A laser machining apparatus as claimed in claim 1, wherein the laser machining apparatus further comprises a scanning strategy controller for controlling at least one of incident laser beam power, incident laser beam pulse repetition rate, and galvanometer scanning speed during machining of a workpiece. 13. A laser machining apparatus as claimed in claim 1, further comprising a gas assist device for at least one of improving machining speed, improving removal of machining debris, and enhancing strength of the machined workpiece. 14. A laser machining apparatus as claimed in claim 1, further comprising a coating device for applying a protective sacrificial coating to a surface of the workpiece prior to laser machining for protecting the workpiece surface from debris produced during laser machining and facilitating removal of debris from the workpiece surface subsequent to laser machining. 15. A laser machining apparatus as claimed in claim 14, further comprising a coating removal device for removal of the protective sacrificial coating subsequent to laser machining. 16. A laser machining apparatus as claimed in claim 1, wherein the laser machining apparatus is arranged for dicing silicon wafers. 17. A laser machining apparatus, as claimed in claim 1, wherein an effective focal depth of the laser beam is increased. 18. A laser machining apparatus as claimed in claim 16, arranged to reduce a dicing kerf width thereby increasing a maximum numbers of dies per wafer. 19. A laser machining apparatus, as claimed in claim 1, wherein the laser beam is characterized by an effective machining focal depth and an increased effective machining focal depth achieves increased aspect ratio micromachining of vias and increased throughput. 20. A laser machining apparatus as claimed in claim 1, arranged for scribing wafers to remove material. 21. A focusing apparatus for focusing an incident polarised optical beam, the apparatus comprising optical plate polarising beam splitter for splitting the incident optical beam to form a first optical beam and a second optical beam; optical beam modifying optics comprising an arcuate light reflecting device for providing the second optical beam with a different divergence or convergence from that of the first optical beam; focusing optics for focusing the first optical beam at a first focus on an optical axis of the focusing optics and for focusing the second optical beam at a second focus on the optical axis, such that the first focus and the second focus fall at different locations on the optical axis, the first laser beam and the second laser beam interfering to form interference fringes; and, imaging optics and an associated controller for using an image of the interference fringes to align the first focus and the second focus on the optical axis. 22. An apparatus as claimed in claim 21, wherein the first focus and the second focus are on a common optical axis of the focusing optics. 23. An apparatus as claimed in claim 21, wherein the arcuate light reflecting device comprises a convex mirror. 24. An apparatus as claimed in claim 1, wherein the plate polarising beam splitter comprises a polarisation dependent layer for substantially reflecting the first optical beam with a first polarisation component and substantially transmitting the second optical beam with a second polarisation component. 25. A method of laser machining a workpiece comprising the steps of: a. splitting an incident polarised laser beam to form a first laser beam and a second laser beam using a plate polarising beam splitter; b. modifying at least the second laser beam to provide the second laser beam with a different divergence or convergence from that of the first laser beam using an arcuate light reflecting device; c. providing focusing optics; d. using the focusing optics to focus the first laser beam at a first focus on an optical axis of the focusing optics and for focusing the second laser beam at a second focus on the optical axis, such that the first focus and the second focus fall at different locations on the optical axis; and e. using a galvanometer to scan the first laser beam and the second laser beam across the workpiece to machine the workpiece. 26. A method as claimed in claim 25, comprising a further step of aligning the first and second foci on an optical axis of a scanning lens associated with the galvanometer using imaging optics and an associated controller for using an image of interference fringes formed by interference of the first laser beam and the second laser beam. 27. A method as claimed in claim 25, comprising a further step of controlling at least one of incident laser beam power, incident laser beam pulse repetition rate, and galvanometer scanning speed during machining of a workpiece. 28. A method as claimed in claim 25, wherein the arcuate light reflecting device comprises a convex mirror. 29. A method as claimed in claim 25, wherein the step of splitting the incident laser beam comprises using a polarisation dependent layer for substantially reflecting the first laser beam with a first polarisation component and substantially transmitting the second laser beam with a second polarisation component. 30. A method as claimed in claim 25, comprising a further step of using a translation table to move the workpiece with respect to the first laser beam and the second laser beam. 31. A method as claimed in claim 25, comprising a further step of providing a gas assist device for at least one of improving machining speed, improving removal of machining debris, and enhancing strength of the machined workpiece. 32. A method as claimed in claim 25, comprising a further step of applying a protective sacrificial coating to a surface of the workpiece prior to laser machining. 33. A method as claimed in claim 32, comprising a further step of removing the protective sacrificial coating subsequent to laser machining. 34. A method as claimed in claim 25, arranged for dicing silicon wafers. 35. A method as claimed in claim 25, wherein a distance between the first focus and the second focus is between millimeters and tenths of microns. 36. A method as claimed in claim 25, wherein a distance between the first focus and the second focus is selectable by selecting a radius of curvature of the arcuate light reflecting device. 37. A method as claimed in claim 25, wherein the laser beam is characterized by a focal depth that is sufficient for high aspect ratio micromachining. 38. A method as claimed in claim 34, wherein a dicing kerf is sufficiently reduced to increase a maximum number of dies per wafer. 39. A method as claimed in claim 25, arranged for high aspect ratio micro-via drilling in silicon wafers. 40. A method as claimed in claim 25, arranged for scribing wafers for removal of material from the wafer. 41. A method of focusing an incident polarised optical beam, comprising the steps of: a. splitting the incident polarised optical beam to form a first optical beam and a second optical beam using a plate polarising beam splitter; b. modifying at least the second optical beam for providing the second optical beam with a different divergence or convergence from that of the first optical beam using an arcuate light reflecting device; c. providing focusing optics; and d. using the focusing optics to focus the first optical beam at a first focus on an optical axis of the focusing optics and to focus the second laser beam at a second focus on the optical axis such that the first focus and the second focus fall at different locations on the optical axis, the first laser beam and the second laser beam interfering to form interference fringes; and e. using imaging optics and an associated controller that use an image of the interference fringes to align the first focus and the second focus on the optical axis. 42. A method as claimed in claim 41, wherein the arcuate light reflecting device comprises a convex mirror. 43. A method as claimed in claim 41, wherein the step of splitting the incident optical beam comprises using a polarisation dependent layer for substantially transmitting the first optical beam with a first polarisation component and substantially reflecting the second optical beam with a second polarisation component.
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