Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/50—Working by transmitting the laser beam through or within the workpiece
  • B23K26/53—Working by transmitting the laser beam through or within the workpiece for modifying or reforming the material inside the workpiece, e.g. for producing break initiation cracks
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/0006—Working by laser beam, e.g. welding, cutting or boring taking account of the properties of the material involved
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
  • B23K26/06—Shaping the laser beam, e.g. by masks or multi-focusing
  • B23K26/062—Shaping the laser beam, e.g. by masks or multi-focusing by direct control of the laser beam
  • B23K26/0622—Shaping the laser beam, e.g. by masks or multi-focusing by direct control of the laser beam by shaping pulses
  • B23K26/0624—Shaping the laser beam, e.g. by masks or multi-focusing by direct control of the laser beam by shaping pulses using ultrashort pulses, i.e. pulses of 1ns or less
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
  • B23K26/06—Shaping the laser beam, e.g. by masks or multi-focusing
  • B23K26/062—Shaping the laser beam, e.g. by masks or multi-focusing by direct control of the laser beam
  • B23K26/0626—Energy control of the laser beam
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
  • B23K26/06—Shaping the laser beam, e.g. by masks or multi-focusing
  • B23K26/073—Shaping the laser spot
  • B23K26/0736—Shaping the laser spot into an oval shape, e.g. elliptic shape
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/36—Removing material
  • B23K26/38—Removing material by boring or cutting
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/36—Removing material
  • B23K26/40—Removing material taking account of the properties of the material involved
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B33/00—Severing cooled glass
  • C03B33/02—Cutting or splitting sheet glass or ribbons; Apparatus or machines therefor
  • C03B33/0222—Scoring using a focussed radiation beam, e.g. laser
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B33/00—Severing cooled glass
  • C03B33/02—Cutting or splitting sheet glass or ribbons; Apparatus or machines therefor
  • C03B33/04—Cutting or splitting in curves, especially for making spectacle lenses
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K2103/00—Materials to be soldered, welded or cut
  • B23K2103/50—Inorganic material, e.g. metals, not provided for in B23K2103/02 – B23K2103/26
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K2103/00—Materials to be soldered, welded or cut
  • B23K2103/50—Inorganic material, e.g. metals, not provided for in B23K2103/02 – B23K2103/26
  • B23K2103/56—Inorganic material, e.g. metals, not provided for in B23K2103/02 – B23K2103/26 semiconducting
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P40/00—Technologies relating to the processing of minerals
  • Y02P40/50—Glass production, e.g. reusing waste heat during processing or shaping
  • Y02P40/57—Improving the yield, e-g- reduction of reject rates

Definitions

• the present invention generally pertains to a method for processing of material by use of a pulsed laser, wherein micro-cracks with defined orientation are effected in the material by applying laser beam pulses with a spatial distribution of laser power across its beam cross section having greater spatial extent in a first direction relative to an orthogonal second direction so that precise cutting of the material along a designated processing path is enabled with high speed.
• controlled fracture technique is a well suitable method for machining of those materials.
• the ablation rate i.e. the processing speed of the direct ablation method
• the laser average power is scaled with the laser average power and normally limited to several mm/s .
• slow processing speed the formation of cracks
• machining of glass substrate is an interesting alternative to the direct ablation process.
• An idea of fast cutting of a display glass where the sample is pre-processed using femtosecond laser pulses prior to glass cleaving was proposed by Ahmed et al . (F. Ahmed, M.S. Lee, H. Sekita, "Display Glass Cutting by Femtosecond Laser induced single shot periodic void array", Appl . Phys . A (2008) 93, 189- 192) .
• the maximum processing speed achieved in this study was 15 mm/s. The speed has been limited by the minimum distance between voids, because it was not possible to cleave the sample when void period was larger than 10 ym.
• filamentation are known for being used for cutting of thin borosilicate glass substrate and for production of simple 3D parts from different types of glass.
• a more precise processing of the material particularly in terms of quality of a cutting edge, along a desired processing path with higher processing speed (e.g. > 15 mm/s) is enabled.
• a further object of the invention is to provide a laser cutting method which enables to cut curvilinear or other shape contours in a transparent or semi-transparent
• the invention relates in one aspect to cutting plates, wafers and/or substrate using formation and controlling of micro defects orientation inside of a transparent material. This can be used for the straight cut as well as for producing of the curvilinear and/or internal closed shape features in the material.
• the invention generally relates to a method for processing of in particular transparent or semi-transparent (with respect to a wavelength of the pulsed laser) material by use of a pulsed laser.
• the method comprises generating a series of (ultra-short) laser pulses, in particular laser pulses with pulse
• each laser pulse is focussed so that respective focal points of the focussed laser pulses comprise pre-defined spatial relations to a first surface of the material (in particular regarding a z-axis corresponding to a thickness of the material) .
• each laser pulse is
• Each emitted laser pulse causes a respective micro-crack within the (in particular fragile) material.
• the main physical effect, which allows coupling of laser energy into transparent or semi-transparent material, is nonlinear absorption.
• Nonlinear absorption allows
• the respective wavelengths of the emitted laser pulses correspond to a wavelength-transparent or wavelength-semi-transparent range of the material to be processed.
• the wavelength of the emitted laser light is adapted according to the transparency or semi-transparency of the material.
• the laser pulses are emitted with one common wavelength, e.g. in the near-infrared region for processing of glass.
• Fig 1 shows a typical defect inside of a glass material 100 induced by application of one femtosecond laser pulse at 1040 nm as known from prior art.
• the used laser beam here comprises a fully symmetrical circular beam profile. Due to that circular profile the occurring defects consist of a set of radiant cracks 102 around the generated channel 101. The maximum size of such cracks typically is of about 10 ym length. Since controlling the type and the shape of the micro defect inside of glass can not be realised by
• each laser pulse is shaped regarding its beam profile so that a cross sectional area, which is defined by a cross section of the laser pulse orthogonal to its propagation direction in the focal point, is of particular shape and has a main extension axis of significantly greater extent than a minor extension axis, in particular wherein the minor extension axis is orthogonal to the main extension axis (i.e. the beam profile is non-circular) .
• a major micro- crack is effected by each laser pulse, the major micro- crack having a lateral extension basically oriented
• each laser pulse is emitted so that the orientation of its main extension axis in the focal point corresponds to a pre-defined orientation relative to an orientation of a respective tangent to the processing path at the particular processing point.
• processing of material preferably glass, using a non- circular laser beam.
• each laser pulse is shaped regarding its beam profile so that a cross sectional area, which is defined by a cross section of the laser pulse orthogonal to its propagation direction in the focal point, is of particular shape and has a main extension axis of significantly greater extent than a minor extension axis, in particular wherein the minor extension axis is orthogonal to the main extension axis (i.e. the beam profile is non-circular with a preferred (main) extension axis) .
• a cross sectional area which is defined by a cross section of the laser pulse orthogonal to its propagation direction in the focal point
• main extension axis of significantly greater extent than a minor extension axis
• the minor extension axis is orthogonal to the main extension axis (i.e. the beam profile is non-circular with a preferred (main) extension axis) .
• main extension axis i.e. the beam profile is non-circular with a preferred (main) extension axis
• the major micro-crack having a lateral extension basically oriented according to the direction of the main extension axis of the cross sectional area of the respective pulse in the focal point and the lateral extent of the major micro-crack is significantly greater than the extent of the respective main extension axis of the cross sectional areas in the focal point, the lateral extent is in a range of 3-30 times the length of the respective main extension axis.
• each laser pulse is emitted (irradiated on the material) so that the orientation of its main extension axis in the focal point corresponds to a pre-defined orientation relative to an orientation of a respective tangent to the processing path at the particular processing point.
• the cross sectional area particularly is defined by a distance to the centre of the laser beam which corresponds to a decrease of the laser peak power to an half (full width half maximum, FWHM) or to 1/e 2 of that power (Gaussian beam profile) .
• the reference 1/2 or 1/e 2
• the cross sectional area as defined above is related to a corresponding cross section through the laser beam in the focal point or the focal plane, respectively.
• one single laser pulse of the series of laser pulses comprises a pulse energy of at least 10 ]i , particularly more than 30 or 40 ]iJ, and is a femtosecond laser pulse or at least a pulse with a duration shorter than 10 ps which results in the lateral extent of the major micro-crack being significantly greater than the extent of the respective main extension axis of the laser pulse cross section .
• Cutting in sense of processing a material e.g. a glass or sapphire substrate, according to the invention, may
• the laser beam is spatially shaped to a collimated elliptical beam shape, wherein the intensity profile is Gaussian in both axes with a major spot diameter around 2.18 times bigger than minor spot diameter.
• major micro-cracks having a lateral extend of 3-30 times the length of the respective main extension axis are caused.
• the sample may preferably be moved with respect to a focal spot at a speed of up to 6 m/s .
• (full) symmetry of the cross sectional area is understood to be rotationally symmetrical in continuous manner (i.e. independent from a grade of rotation) , wherein asymmetry is understood to also be rotational symmetric but only in discrete manner (e.g. by each 180° of rotation) which corresponds to an embodiment of the beam profile of the laser pulses.
• asymmetry is understood to also be rotational symmetric but only in discrete manner (e.g. by each 180° of rotation) which corresponds to an embodiment of the beam profile of the laser pulses.
• a symmetric body is to be
• micro-defects micro- cracks
• the laser pulses are shaped so that a defined main extension direction is given by the cross sectional area.
• the pulses may have kind of elongated shapes like a stripe, particularly a line with little extension relative to the direction of the line, or like a rectangle (wherein - of course - the longer sides of the rectangle define the main extension axis) or like an ellipse with a major axis and a minor axis as described herein below.
• cross sectional area may be of any shape
• orientation of the main extension axis is correlated with the orientation of a tangent on the processing path, each major micro-crack effected (caused) thereby also correlates as to its orientation to the orientation of a tangent to the processing path, particularly at the respective
• the processing path to which the method according to the invention basically (but not exclusively) is related, is embodied as a curvilinear (curved) processing path. Moreover, a major micro-crack which is generated by
• a major crack effected by the present method is of significantly greater lateral size than a major axis of its cross sectional area. Filamentation aims to generating accurate channels of diameters in the region of the size of the beam cross section throughout the entire material (in z-direction) , wherein the major cracks to be effected in context of the present invention are desired and effected with notable greater lateral extension
• the respective major micro- cracks are effected with lateral lengths significantly larger than the length of the respective main extension axis of the cross sectional areas in the focal point.
• the lateral length relates to a length of the respective major micro-cracks in a direction basically parallel to a focal plane.
• the lateral lengths are in a range of 3-30 times the length of the respective major axes of the laser beam, i.e. the lateral length is greater than the extension of the area modified by the laser (where the laser pulse hits the material) .
• the distance at/in the material between two successive laser pulses can be chosen to be
• Cutting speed is defined as a velocity of laterally moving the laser beam relative to the substrate to be processed, which mathematically is defined as a product of the distance between two successive pulses at the substrate and the repetition frequency the laser pulses are emitted with.
• the distance between two successively emitted pulses directed to the material is chosen to be greater than the length of one major micro-crack caused by such laser pulse.
• a distance between the laser system i.e. a point where the laser beam is emitted by the laser system
• the first surface of the material, which faces the laser system corresponds to less than or equal to the focal length of the laser beam
• a distance between the laser system and the second surface, which second surface is turned away from the laser system corresponds to more than or equal to the focal length of the laser beam, for providing a well focussed beam e.g. in a defined focal plane.
• the laser pulses are focussed and emitted so that the focal points of the emitted laser pulses lie in different planes within the material. That approach allows processing of e.g. specifically shaped material or of material which comprises defined structures.
• the laser pulses can be focussed so that at least two focal planes are defined in the material and respective focal points of the focussed laser pulses lie in the two focal planes, or - while directing the laser pulses to the material - variable focussing can be performed with changing a focal length using a variable-focus lens to achieve variable focusing spots in z-direction.
• variable-focus lens enables to provide different focal lengths along an emission direction of the laser beam on demand, for instance by changing the optical properties of the lens the focal length changes as well.
• the optics of such multi-foci lens defines at least two focal points of different focal length at the same time.
• the laser beam is focussed so that the focal point lies above but still near the first surface or below but still near the second surface.
• the laser pulses may preferably be ultra-short laser pulses with pulse durations of ⁇ Ins, particularly ⁇ 10 ps or in the femtosecond region.
• the material to be processed in particular is in form of a transparent
• a lateral propagation of a crack in the material can be controlled and defined with respect to its direction by applying successive laser pulses with defined lateral distance and defined orientation relative to each other.
• the induced crack propagates basically according to the orientation of a projection of the main extension axis of the elongated cross sectional area in the focal point of a following laser pulse, i.e. in case the laser pulse impinges orthogonally on the surface (the propagation direction of the laser beam is orthogonal to the surface of the material)
• the crack propagates basically according to the orientation of the main extension axis of the cross sectional area (e.g. of the elliptical beam profile) .
• the method according to the invention provides for precise cutting of a curvilinear contour and of
• the above method of laser processing may preferably be realised with a laser system for generating ultra-short laser pulses, i.e. pulses with pulse durations in the femto- or picosecond order, wherein the system has to be embodied in specific manner for performing the method.
• the system in general may comprise a mode-locked laser
• a generator with e.g. a ytterbium- or neodymium-doped laser medium like ytterbium doped wolframate (e.g. Yb:KYW or Yb:KGW) or neodymium doped vanadate (e . g . d : YVO 4 ) .
• a ytterbium- or neodymium-doped laser medium like ytterbium doped wolframate (e.g. Yb:KYW or Yb:KGW) or neodymium doped vanadate (e . g . d : YVO 4 ) .
• ytterbium- or neodymium-doped laser medium like ytterbium doped wolframate (e.g. Yb:KYW or Yb:KGW) or neodymium doped vanadate (e
• each laser pulse is adapted depending on the course of the processing path by a defined rotation of the beam profile.
• the beam profile is particularly rotated around the centroid of the cross sectional area. Such rotatability of the beam profile provides material
• an elongated, non-circular (e.g. elliptical or stripe like shaped) beam For instance, an elliptical beam is rotated by 15° per step in order to provide processing along a curvilinear path with respective curvature.
• a change of the orientation of the elliptical beam relatively to the sample to be processed leads to a change in the orientation of the effected micro-cracks inside of the sample, e.g. glass sample.
• the change of the orientation of the cross section for the laser pulses i.e. of the beam profiles, for instance is realised by a specific variable arrangement of optical or electro-optical elements (e.g. mirror, prism etc.) and/or by specific adaptations concerning the coupling the laser beam out of the laser system.
• Such adaptation of the orientation may be provided by a beam defining unit.
• the orientation of the main extension axis of the first pulse (s) applied to the material may significantly influence the processing, in particular influences the way of fracturing of the material with respect to laser cutting.
• the orientation of the main extension axis of the first emitted pulse is to be set in such manner that the orientation of such main extension axis corresponds to the crystalline structure of the material (i.e. corresponds to an orientation of the crystals in the material) .
• the processing path and/or the orientation of the crystalline material to be processed relative to the laser system may be adapted accordingly.
• each laser pulse can be emitted with a pre-defined orientation of its main extension axis which
• pre-defined orientation corresponds to an angular
• the propagation of a continuous crack in the material can be controlled concerning particular materials like glass (e.g. in case the effected major micro-cracks are not adjoining, but there is a defined gap between the major micro-cracks), i.e. the propagation of the crack (fracture of the
• the pulses are placed in well defined manner.
• the laser pulses are emitted so that a lateral distance on the surface or in a plane relative to the first surface and/or with reference to the focal points between at least two of the laser pulses, which are successively emitted,
• the length of the effected major micro-crack by one laser pulse corresponds to 3-30 times the distance (in the focal plane) from the beam centre to a point along the main extension axis of the cross section at which the power of the laser e.g. is 1/e 2 of the peak power and the distance between two of such pulses basically is the average of the lengths of the effected major micro- cracks, the effected major micro-cracks are touching each other (are adjoining) .
• the length of the main extension axis of a pulse in the focal point is in the range of 2-3 ⁇ and the effected major micro-crack has a lateral (parallel to the first surfaces of the material and/or to the focal plane) length in the rage of 10-60 ⁇
• the laser pulses are applied with a distance between each others corresponding to a respective value of the rage of 10-60 ⁇ .
• the laser pulses are directed so that the effected major micro-cracks are laterally touching or nearly touching each other in order to provide a precise processing or cutting of the material.
• the micro-cracks comprise lengths significantly greater than the length of the main axes of the cross sections of respective pulses, the distance between the pulses on the surface is chosen correspondingly bigger.
• the laser pulses are emitted so that the lateral distance between at least two of the laser pulses (with reference to their focal points or on the first surface, respectively) , which are successively emitted, is bigger than the average of the lengths of the main extensions, particularly major axes, of respective cross sectional areas of these pulses in the focal points.
• respective major micro-cracks are created with a defined spacing in between or respective major micro-cracks are adjoining (basically no distance between the micro-cracks and also basically no
• the major micro-crack effected by a first of the successive laser pulses is extended due to the major micro-crack induced by a second of the
• the laser pulses are emitted so that successively emitted laser pulses impinge on the surface with a relative lateral distance as described above. Consequently, (only) one single laser pulse is directed to each respective processing point, wherein a defined distance to a preceding and to a
• a distance of successive (neighbouring) processing points on the processing path corresponds to a lateral distance as outlined above.
• the distance between two processing points may correspond to an average of the lateral lengths of the major micro-cracks which are caused by pulses applied at these points.
• At least one of the laser pulses is shaped so that its cross sectional area is of elliptical shape (in its focal point) and the main extension axis is defined by (the direction of) the major axis of the elliptical cross sectional area, i.e. the major axis corresponds to the main extension axis.
• the laser beam (a laser pulse respectively) is configured (shaped) so that the relation of the length of the major axis to the length of the minor axis of the
• (elliptical) cross sectional area is at least 1.1 : 1 or
• Glass cutting according to the method of the invention for example shows reliable good results regarding cutting quality and processing speed, wherein an ellipticity of the beam profile of 2.18 is used, i.e. the ratio of the length of the major axes to the length of the minor axis is
• the relation of the length of the major axis to the length of the minor axis of the cross sectional area is at least 2 : 1, particularly is in the range of 2 : 1 to
• laser parameters particularly are adapted to the type of material.
• the lengths of the main extension axes e.g. the ellipticity of a Gaussian laser beam profile
• pulse repetition rate e.g. the pulse repetition rate
• pulse durations e.g. the pulse duration of a Gaussian laser beam profile
• pulse energies are adjusted regarding the properties of the material to be processed, in particular regarding a chemical composition and/or a thickness of the material, so that each laser pulse effects a respective major micro-crack with
• micro-cracks with defined lengths can be produced in the material and processing, e.g. cutting, of the material can be performed in a more reliable and optimised way.
• a single laser pulse of the series of laser pulses which is directed to the material, effects a major micro-crack with a lateral length of at least 3 ⁇ , particularly at least 10 ⁇ , particularly wherein the single laser pulse comprises a pulse energy of about 40 ]iJ, a pulse duration in the femtosecond order and the material is transparent or semi- transparent, in particular is made of strengthened
• a single laser pulse of the series of laser pulses which is directed to the material, causes a micro-crack with an extension as to the direction normal to the surface of the material in a range of 10 to 50 ⁇ , particularly in a range of 10 to 30 ⁇ .
• Concerning material processing is in form of cutting the material, such cutting of the material - according to the invention - is performed by inducing successive major micro-cracks along the processing path in adjoining manner, wherein a cutting edge is defined by a course of the successive major micro-cracks in the material.
• the cutting of the material is performed with a lateral cutting speed regarding the surface of the material in a range of 0.2 to 10 m/s, in particular 0.2 - 3 m/s, the cutting speed depends at least on the extent of the main axis (i.e. ratio of main and minor extension axis) of the cross sectional area, particularly on the ratio of the lengths of the major axis and the minor axis of the cross sectional area, on the lateral (and/or normal) length of the effected micro-cracks (micro-defects) , on the pulse energy, on the pulse duration and on a pulse repetition rate.
• the main axis i.e. ratio of main and minor extension axis
• the lateral (and/or normal) length of the effected micro-cracks micro-defects
• the cutting of the material may be performed by repeated emitting of the laser pulses along the processing path, wherein the major micro-cracks effected by firstly
• directing the laser pulses along the processing path propagate at least in the direction normal to the focal plane when directing the laser pulses along the processing path for a second time or for further times, in particular wherein the position of the focal point is adapted for each directing of the laser pulses along the processing path.
• each such scan is performed at a different distance between the laser system and the material sample for providing the series of pulses to be applied with adapted focal distance.
• the focal distance is adapted by adjusting respective optical elements. E.g. when scanning the path for the second time the distance is increased so that the focal point of the laser beam no longer is in the region of the second surface (which is turned away from the point of laser emitting) of the material but lies rather "inside" of the sample (closer to the first surface (which faces the point of laser
• "Gorilla" Glass by Corning Inc., USA
• the ultra-short laser pulses comprise an elliptical shape with an ellipticity of about 2.18.
• the pulse energy is 34 ⁇ iJ and the pulses are emitted with a frequency (repetition rate) of 3.3 kHz.
• a scanning speed of about 100 mm/s is reached, wherein the cutting path is to be processed for four times and thus an
• Such cutting is performed using an average laser power of 140 mW. By increasing the power to 8 W, and increasing repetition rate to 200 kHz, a cutting speed of 1.5 m/s could be reached.
• bursts of laser pulses are used in order to provide larger micro- cracks with each scan.
• a burst of laser pulses with a defined burst energy i.e. the sum of pulses of the burst comprises a defined total burst energy
• the burst of laser pulses being directed at a designated point of the material, particularly at a processing point, wherein a defined inducement
• the burst energy is of at least 10 ]i .
• the laser pulses of the burst are generated with a pulse-to-pulse time lag in a range of 1 to 100 ns, in particular in a range of 10 to 20 ns .
• Such time lag is preferably chosen in dependency on a stress relaxation time of the material. I.e. if a material with differing
• the pulse-to- pulse time lag may be adapted accordingly.
• such a burst may cause a crack in the material with an extension as to the direction normal to the surface of the material in a range of 10 to 150 ⁇ , particularly in a range of 40 to 100 ⁇ .
• the size of the effected crack depends on the used material and the laser configuration.
• the power profile is defined by an exponential decay of pulse energies of the pulses of the laser burst (i.e. pulses within the burst), in particular wherein the energy of an initial burst pulse is in a range of 15% to 30%, in particular in a range of 20% to 25%, of the burst energy, or an exponential increase of pulse energies of the pulses of the laser burst, or constant pulse energies within the burst.
• a burst of above may comprise at least five sub-pulses, which are generated with defined pulse-to-pulse time lag, wherein the time lag may vary or be constant for all pulses.
• the first emitted pulse of the sub-pulses may comprise about 23% of the entire burst energy and
• successive pulses may comprise successively deceasing energies.
• the laser pulses of the burst are generated with a defined pulse duration profile.
• the duration profile can be defined by a pulse-to-pulse increase or decrease of pulse durations (pulse lengths) of the pulses of the laser burst or can be defined by both a pulse-to-pulse increase and decrease of pulse durations during one burst of laser pulses.
• Such increase and/or decrease can be provided with particular increasing and decreasing rates.
• the pulse durations (and energies) can be adjusted so that pulse energies of pulses in the burst are not changing due to change of pulse durations.
• particular processing parameters can be realised which e.g. require quite constant pulse energies but show improved results when applying increasing and/or decreasing pulse durations over one burst.
• an increasing pulse duration of a 14-pulses burst (a burst comprising fourteen sub-pulses) starting at 350 fs and increasing up to 2.5 ps leads to much better quality in terms of cross-sectional surface roughness.
• the laser pulses may particularly be directed (emitted) so that the centroid of the cross sectional area of each laser pulse is located on the surface or inside of the material depending on the designated processing point, in particular wherein the laser pulses are directed so that the centroid of each cross sectional area lies on the processing path or corresponds to the respective processing point.
• a compensation plate is provided at the first surface of the material (the surface facing the laser source) , wherein the compensation plate comprises defined thickness and light transmitting (or absorbing) properties and the laser pulses pass the compensation plate prior to reaching the material, in particular wherein the light transmitting properties, in particular a refractive index, correspond to those of the material to be processed.
• the compensation plate may directly be put on the material, i.e. having contact with the material, or a defined gap (e.g. filled with air or a particular processing medium) between the compensation plate and the material may be provided .
• the invention also relates to a laser system for processing of material, in particular transparent or semi-transparent material regarding a wavelength of the laser (in sense of the used laser wavelength), in particular fragile material.
• the laser system comprises a laser source for generating a series of ultra-short laser pulses with defined beam profile, in particular with pulse durations of less than 1 ns (or ⁇ 100 ps) , in particular pico- or femtosecond laser pulses, and a beam defining unit for directing each laser pulse to the material with defined reference to a
• each laser pulse respectively assigned processing point of a processing path and for focussing each laser pulse so that respective focal points of the focussed laser pulses comprise pre-defined spatial relations to a first surface of the material (e.g. focussing each laser pulse so that respective focal points of the focussed laser pulses lie on a first surface of the material or between the first and an opposite second surface of the material) .
• Each respectively focussed laser pulse which is directed to the material causes (effects) a respective micro-crack within the material.
• the laser source is designed in a manner such that each laser pulse is shapeable regarding its beam profile so that a cross sectional area, which is defined by a cross section of the laser pulse in its focal point orthogonal to its propagation direction, is of particular shape (i.e. the beam profile is of e.g.
• the major micro-crack is effected by each laser pulse, the major micro-crack having a lateral extension basically oriented according to the direction of the main extension axis of the cross sectional area of the
• the system provides a processing function which is designed to control the beam defining unit, and particularly the laser source, in a manner such that each laser pulse is emittable so that the orientation of its main extension axis in the focal point corresponds to a pre-defined orientation relative to an orientation of a respective tangent to the processing path at the assigned processing point.
• the laser system particularly comprises a controlling unit for controlling the defining unit and the laser source according to the above features of beam shaping and
• the processing function is designed in a manner such that an above-described method is performed on execution of the processing function.
• the laser system comprises a table which is designed to be movable in at least two directions (x- and y-direction) relative to the laser source and/or to the beam defining unit, the table providing desired
• the invention relates to a computer programme product having computer-executable instructions for
• fig. 1 shows a cross cut through a sample processed with a circular laser pulse as known from prior art
• fig . 2 shows a cross cut through a transparent laser pulse
• figs. 3a-b show laser emitting units for emission
• figs. 4a-b show schematic representations of laser cutting of curvilinear structures according to the invention ;
• figs. 5a-e show the dependency of the lateral size on the number of emitted elliptical pulses according to the invention;
• fig. 6 shows an embodiment according to the invention of a power profile of a burst of laser pulses;
• fig. 7a-c show possible variations of pulse lengths of laser pulses of a burst of laser pulses according to the invention;
• fig. 8 shows a measurement of a beam profile used with the present invention;
• fig. 9 shows an interaction of an invention-like
• fig. 10 shows a specific method of laser cutting of transparent material according to the invention
• Fig. 2 shows a cross cut through a transparent material 1, e.g. chemically strengthened glass like "Xensation"
• micro-crack 12 As an effect of the energy brought into the material 1 by the laser pulse in defined manner regarding the beam profile, particularly regarding pulse duration and/or pulse energy, one single major elongated micro- defect 12 (micro-crack 12) is caused in the material 1.
• the material to be processed is formed by a conductive and transparent oxide film which is used with solar cells or flat panel displays, e.g. an oxide film of ZnO with defined thickness.
• the lateral extension of the micro-crack 12 is significantly greater than the length of the main extension axis (here: major axis) of the cross sectional area 11.
• Such micro-crack 12 occurs by applying an ultra-short laser pulse with a suitable non-circular, elongated beam profile, e.g. elliptical beam profile, in sense of the present invention, particularly by applying more than one pulse at one single point on the material 1.
• the lateral length relates to a length of the micro- crack 12 in a direction basically parallel to a focal plane . It is to be understood that a micro-crack caused by
• a laser pulse with a (e.g. elliptical) beam profile with a main extension axis longer than its minor extension axis according to the invention in the end is well defined, particularly regarding its size, due to an interaction of material and laser properties.
• the size of the cross sectional area of the laser beam at the focal point may be defined by a distance to the centre of the laser beam (channel 15) which e.g. corresponds to a
• Fig. 3a shows a laser emitting unit 20 for emission of ultra-short (e.g. femtosecond, particularly ⁇ 600 fs) laser pulses 22 with defined beam profile according to the invention.
• the unit 20 is designed so that an orientation of an emitted laser beam 21 can be varied in defined manner.
• the beam 21 can be moved over a surface of a substrate 1 to be processed according to a defined pattern, particularly along a defined processing or cutting path.
• the emitting unit 20 e.g. comprises a scanning head.
• the emitting unit 20 provides the laser beam 20 with a beam shape having a cross sectional area which is defined by a cross section through the laser beam 20 orthogonal to its propagation direction in the focal point of particular non-circular shape, wherein a length of an axis corresponding to a main extension of that shape is greater than a length of a different (orthogonal) axis corresponding to a minor extension of the desired shape.
• the laser beam 21 is emitted with constant direction from the laser source 20, wherein a table 19, which carries the substrate 1, is provided and the table 19 is movable in x- and y-directions and/or rotatable relative to the laser source 20.
• processing according to a given processing path is enabled by correspondingly moving the sample 1 (and thus defining the scanning speed) while emitting laser pulses with defined repetition frequency and orientation of the beam profile.
• the distance between the laser- emitting-point and the table 19 is adjustable by either moving the laser source 20 or the table 19 (or both) along the z-axis .
• the repetition rate and the scanning speed preferably are adapted so that the distance between two successive laser pulses 22 on the surface (i.e. the distance between the centres of these pulses on the surface) or in the focal plane, which is located between the upper and the bottom surface of the substrate 1, corresponds to an average length of the lengths of the major micro-cracks in the material (transparent or semi-transparent materials like types of glass), which are effected by these laser pulses.
• the length of a major micro-crack, which is caused by such a laser pulse here basically is of about 5-10 times the length of the respective main axis of the cross sectional area - of the elongated cross sections of the pulses - (for better illustration, the laser spots here are illustrated in oversized manner compared to caused micro-cracks) , wherein the cross sectional area is defined by the full width half maximum (FWHM) value with respect to the
• the length of an effected major micro-crack depends on several factors like pulse energy, pulse duration, number of applied pulses at one identical point on the material and material properties.
• the length of a major micro-crack basically corresponds to a multiple of the length of the respective main extension axis.
• the caused major micro-cracks by such an emitted series of laser pulses can be applied contiguous so that there is no space in between the respectively effected major micro-cracks (on the surface of the material) by placing the laser spots with respective (corresponding to the ratio of the lengths of the major micro-cracks and the main extension axes) distance.
• the laser pulses 22 may be placed with a defined space between their cross sectional areas and between the effected major micro-cracks on the
• processing (cutting) speed can be reached.
• the material may be a kind of visually transparent or semi-transparent (at least with respect to a wavelength-region of about 1040 nm) material (e.g.
• Xensation glass with a thickness of 0.7 mm and the laser source 20 is operated with an average power of 60 mW, wherein each pulse has energy of 24 ⁇ J and wavelength of 1040 nm, and a repetition rate of 2 kHz.
• a scanning speed of 100 mm/s can be reached by effecting micro-cracks with a lateral length of about 50 ⁇ , wherein the effected micro-cracks propagate through the entire thickness of the material and thus, a clean cut is provided.
• a processing speed of about 10 m/s can be realised.
• a subset of laser pulses (burst, see e.g. fig. 6) may be applied for every cutting point particularly if material of greater thickness is to be cut.
• Fig. 4a shows a schematic representation of laser cutting of a curvilinear structure according to the invention.
• a series of laser pulses 22 is applied on the material 1 along a designated curvilinear processing path 25 (as the pulses of the series of laser pulses comprise identical properties except of the orientations of their cross sectional areas, only one of the pulses 22 is referenced by number in place of the rest of the shown pulses) .
• the laser pulses 22 are set so that a defined distance between the defined cross sectional areas of each pulse 22 is present.
• the cross sectional area may be defined by a distance to the beam centre at a peak power decrease to 1/e 2 of the peak power.
• each pulse 22 causes a micro-crack in the material 1 the extension of which (regarding the lateral length of the crack) is larger than the length of the major axis of the respective cross sectional area at the focal point.
• a focal plane is defined between a first 2 (facing the laser source) and a second 3 surface (opposite to the first surface 2) of the material 1, wherein the laser pulses 22 are emitted with respective focal points which all lie in such common focal plane.
• each pulse 22 generates a kind of channel 23 throughout the entire material 1 in z-direction.
• the laser pulses 22 impinge according to a direction orthogonal to the first surface 2 of the
• Fig. 4b shows a schematic representation of a top view on the material (first surface 2) as processed similar to as shown in fig. 4a.
• the pulses 22 are applied with such defined relative distance that the generated major micro- cracks 24 basically engage into each other and that one continuous edge is built by the generated major micro- cracks 24 thereby.
• each respective laser pulse 22 is adapted (changed) for to provide a direction of these axes parallel to respective tangents to the processing path 25 or to provide these axes to even be coaxial with such tangents.
• the major axis of each respective laser pulse 22 is set so that it is at least parallel to a tangent to the processing path 25 in a respective processing point 26 of the path 25, wherein each laser pulse 22 is assigned to a defined processing
• any contour can be cut out of the material 1 by using the principle of rotation of the beam profile according to the course of the processing path 25.
• the cutting edge emerges from the series of induced major micro-cracks 24, wherein laser parameters (e.g. pulse energy, repetition rate, pulse duration and shape of the laser pulses) and the properties of the material 1 to be processed (e.g. transparency, thickness and hardness) define the cutting quality and the cutting speed .
• laser parameters e.g. pulse energy, repetition rate, pulse duration and shape of the laser pulses
• properties of the material 1 to be processed e.g. transparency, thickness and hardness
• the material 1 to be cut is thicker than the length of the major micro-crack which is effected in the material 1 along the z-direction by application of one single laser pulse 22, more than one laser pulse 22 can be emitted for each processing point 26 or the pulse energy can be increased in order to provide a micro-crack 24 which penetrates through the whole material 1. This can be done by repeated scanning of the same processing path and/or by applying a laser burst for each processing point.
• a sub- series of laser pulses 22 (burst, see e.g. fig. 6) is emitted for each processing point 26 with defined
• the micro- crack 22 particularly grows laterally along the surface of the material and/or orthogonally to the surface into the material 1 ( z-direction) .
• the laser pulses 22 are applied so that they impinge on the processing points 26 the pulses are assigned to. As shown here for better clearness, the laser pulses 22 are applied with defined offset to the path 25 and to respective processing points 26 along the path 25.
• the laser properties can be adapted while cutting a contour along the processing path 25.
• regions of the processing path 25 which comprise basically linear cutting parts higher pulse energy could be used for effecting micro- cracks with greater lateral lengths, wherein the pulse energy could be reduced when cutting along a curve for providing micro-cracks with smaller size and thus to more precisely generate a curvilinear contour there.
• the pulses may be emitted along the defined processing path so that a defined and basically constant amount of energy is brought into the material per unit of length of the processing path or per unit of area (or volume) of the material.
• figs. 5a-e show the dependency of that lateral size on the number of emitted pulses according to the invention.
• the pulses are of pulse durations in the femtosecond region and are applied with a time lag between two successive pulses (burst frequency) of about 13 ns .
• the processed material is formed by a chemically strengthened glass.
• Fig. 5a schematically illustrates the effected major micro- crack 24 on application of one single pulse. The length of that micro-crack 24 particularly is about 19 ⁇ .
• 5b shows the caused micro-defect 24 with impinging of two pulses at the same point on the material, wherein the length of the micro-defect increases by about 70 %, particularly to up to approximately 32 ⁇ .
• the size of the micro-crack 24 effected thereby would be about 236 % of the size of the micro-crack by one single pulse (about 45 ⁇ ) as shown in fig. 5c.
• the emitting of four pulses leads to a micro-crack size of about 278 % of the initial micro-crack (about 53 ⁇ ) as shown in fig. 5d and the application of more than four pulses, i.e. of multiple pulses, would effect a micro-crack 24 - according to the shown example - with a length of at least 56 ⁇ as
• the total energy brought into one single (processing) point of the material does not depend on the number of applied pulses but is the same for e.g. three and five generated burst pulses.
• the pulse energy of the single pulse according to fig. 5a corresponds to the sum of pulse energies of the two pulses applied in context of fig. 5b.
• the axial size ( z-direction) of the micro-cracks caused by the above use of a burst of pulses e.g.
• the axial length of a micro-crack increases by application of four pulses by a factor of about "3" compared with the axial length of a micro-crack caused by one single pulse. Therefore, the use of a burst of laser pulses leads to a wider range of material to be processable (i.e. which can be cut precisely) with the method according to the
• the properties of the pulses within one burst particularly are adapted according to the kind
• the time period from pulse to pulse (time lag between two successive pulses) is set so that it basically corresponds to or is smaller than the stress relaxation time of the material.
• the time between the pulses of the burst thus should be equal or smaller than the respective stress relaxation time of the material.
• stress relaxation time of chemical strengthened glass is in the region of about 10 - 20 ns and thus the pulses of the burst can be applied with a time lag between two successive pulses of about 13 ns .
• Fig. 6 shows an embodiment of a power profile of a burst of laser pulses being applied for processing of material in context of the present invention.
• five laser pulses are generated within the respective burst, wherein the number of laser pulses within the burst can vary as to processing requirements.
• the pulses within the burst are generated with a defined pulse-to-pulse time delay (lag) At, which e.g. is of about 13 ns .
• the initial pulse of the burst comprises a particular pulse power Pi (and respective pulse energy Ei) , wherein successive pulses in the burst are generated comprising successively
• Figs. 7a-c show possible variations of pulse lengths of laser pulses of a burst of laser pulses.
• Fig. 7a shows an increase of respective pulse durations starting at about 200-300 fs (femtoseconds) of duration for a first burst pulse and ending with a duration of the last laser pulse the burst of about 2700 fs .
• the burst comprises 14 sub- pulses .
• Fig. 7b shows a change of pulse durations in the burst to the contrary, i.e. starting with long durations of about 2700 fs and ending the burst with pulses in the region of 500-200 fs.
• Fig. 7c shows such adjustment of pulse durations of one burst.
• First six pulses are designed to have shorter durations from pulse to pulse resulting in a minimum of pulse length (here: about 250 fs) , wherein the durations for successive (six) pulses increase again.
• the rate of duration decrease or increase can be adjusted
• FIG. 8 shows a measurement of an elliptical beam profile used with the present invention.
• a cross section 31 of a laser beam is shown, which beam is used in form of a laser pulse with defined pulse duration for material processing according to the invention (pulse duration typically is defined based on a FWHM value of the pulse) .
• the beam profile, i.e. the cross sectional area 31, is of elliptical shape with a major axis A and a minor axis B, wherein the length of the major axis A is about 2.2 times greater than the length of the minor axis B.
• Such ellipticity provides the creation of defined basically linear defects (herein called "major micro-cracks") in e.g. glassy materials and, generally, in transparent materials.
• the ratio between the length of the major axis relative to the length of the minor axis is of about 1.5 : 1, 2 : 1, 3 : 1 or even >3 : 1.
• the ratio between the major axis and the minor axis is preferably chosen as to the material to be processed and the optimum regarding the emerging micro-crack size and cutting speed.
• the intensity distribution of the beam profile along the major A and the minor B axis as measured with such an elliptical beam is shown.
• the curve 32 depicts the intensity distribution of the laser radiation in the course of the minor axis B and the curve 33 depicts the intensity distribution of the laser radiation in the course of the major axis A.
• distributions 32,33 significantly differ from each other with view to their widths (e.g. full widths at half
• a cross section of preferably a Gaussian laser beam as shown here is only a schematic representation of the real intensity distribution over the entire laser beam and that the shape of a laser pulse is depicted by a border line along a defined peak power decrease with respect to the maximum value in the centre of the beam cross section.
• the full width at half height/maximum (FWHH) value or a decrease to 1/e of the peak power is used for illustrating the shapes (and size) of laser pulses.
• Fig. 9 shows an interaction between a transparent material to be processed and an ultra-short laser pulse 22 with a cross sectional area in its focal point, the focal plane 4 respectively, of elliptical shape.
• the laser pulse 22 is directed orthogonally to the first surface 2 of the
• a major micro-crack 24 is effected within the material.
• the lateral extension of the micro-crack 24, i.e. an extension at least parallel to the first surface 2 or the focal plane 4 substantially extends the beam diameter with respect to its major axis (in x-direction) .
• the major micro-crack 24 extends in z-direction, but basically is oriented in x- direction .
• Fig. 10 shows a specific method of laser cutting of
• a first series of elliptical laser pulses 22' is emitted to the material 1 along a defined, in particular curvilinear (not shown here) , processing path, wherein the pulses are emitted so that effected major micro-cracks have significant distances between each other and thus, the fracture of the material does not occur after having processed the first series of pulses 22 ' .
• For initiating the fracture of the material 1 at least one further laser pulse 22 ' ' is directed at one of the ends of or at a defined point along the processed processing path and initiates fracture of the material 1.
• the pulse is particularly emitted so that at least one of the already caused major micro-cracks is enlarged by the additional pulse 22 ' ' and thus pushes the break of the material 1 along the processing path.
• the further laser pulse 22 ' ' is generated with use of different laser parameters, e.g. the further pulse 22 ' ' comprises higher pulse energy or a different ratio of its main extension axis relative to its minor extension axis.
• Fig. 11a shows a cross cut through a material 1 being processed according to the method of the present invention. The processing direction is in y-direction. As can be seen, modified areas 41 (only one of which is referenced as to simplification reasons) within the material 1 are generated with each laser pulse interacting with the material 1.
• a length 42 of a respective crack for each modified area 41 is depicted.
• the length 42 of such related cracks are significantly greater than the width of the modified areas 41 (basically corresponding to the main extension axes of the cross sectional areas of the laser pulses) in y-direction.
• Fig. lib shows a topographic measurement (profile) along the line 43, i.e. a profile of the material 1 after laser processing in a plane of modification (y-z plane) and the focal plane (x-y plane) . Shown is the profile height over the respective position in y-direction.
• the peaks of the curve represent topographic properties of the modified areas 41.
• topographic curve corresponds to the distance 44 between the modified areas (distance between two successive laser pulses) . Therefore, roughness mainly increases with each of the modifications 41 but remains comparatively low in regions between such modifications 41.
• process robustness can be improved by increasing the distance 44 between the modified areas 41.
• formation (shape, z-position, etc.) of a next (successive) modified area is influenced by the previous modified area.
• the process window there is defined e.g. by D min ⁇ 3-5 ym pulse distance where formation of the second modified area already is not influenced by the first modified area and particularly D max ⁇ 4-6 ym at which material can still be cleaved in controlled way. That also limits the laser repetition rate, cutting speed, pulse energy etc.
• the process window is limited by only a distance D max » 6 ym (up to e.g. 50 ym) which depends on the
• Fig. 12 shows a further embodiment of material processing according to the invention.
• An additional layer or plate 50 is provided on top of the material 1 to be processed, i.e. on that surface 2 which faces the point of emitting the laser light 21 at the laser system.
• the (complex) refractive index of the material 1 to be processed i.e. on that surface 2 which faces the point of emitting the laser light 21 at the laser system.
• compensation plate 50 ( ni ) is in the same order as, in particular is the same as, the one of the substrate 1 (n 2 ) . Fresnel losses can be reduced when ni is equal to n 2 .
• the light transmitting properties of the compensation plate 50 are preferably chosen to be similar to the substrate.
• the compensation plate 50 may be transparent or semi- transparent regarding the laser wavelength.
• the compensation plate 50 enables to adjust the modified area 41 within the substrate 1 with respect to its position (in z-direction) and shape.
• a combination of applying elliptical laser pulses and such compensation plate 50 with a material to be processed results in further improved processing parameters for e.g. improved glass cutting quality.
• Fig. 13 shows an embodiment of material processing using elongated (e.g. elliptical) laser pulses (with reference to a lateral x- or y-direction) and a variation of focal points for successive pulses.
• elongated (e.g. elliptical) laser pulses with reference to a lateral x- or y-direction
• focal points of elongated laser pulses with reference to a lateral x- or y-direction
• respective pulses lie within two focal planes E and F.
• the change of the location of the focal points in z-direction can be realised from pulse to pulse so that successive pulses are located in different focal planes E or F.
• Such change is preferably realised using a lens able to provide different foci with high changing frequency.
• FIG. 14 shows an embodiment of material processing using non-circular (e.g. elliptical) laser pulses (with reference to a lateral x- or y-direction) and converging (focussing) each laser pulse in at least two focal points (focal planes E and F) along its respective emitting direction (here: z- direction) .
• non-circular (e.g. elliptical) laser pulses with reference to a lateral x- or y-direction
• converging (focussing) each laser pulse in at least two focal points (focal planes E and F) along its respective emitting direction (here: z- direction) .
• Such forming of two focal points for one laser pulse can be provided by a multi-foci lens.
• two modification areas can be caused with application of only one laser pulse which provides for two cracking-centres in different z-positions and thus enables to realise cutting (cleaving) of glass substrates 1 of comparatively large thickness by one single pass of the laser light along a processing path.
• a second pass with different focal length can be avoided. Therefore, a (higher) processing speed of significantly higher efficiency can be realised.

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