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
• • 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
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B33/00—Severing cooled glass
  • C03B33/08—Severing cooled glass by fusing, i.e. by melting through the glass
  • C03B33/082—Severing cooled glass by fusing, i.e. by melting through the glass using a focussed radiation beam, e.g. laser
• • 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
• • 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
  • B23K26/0604—Shaping the laser beam, e.g. by masks or multi-focusing by a combination of beams
  • B23K26/0608—Shaping the laser beam, e.g. by masks or multi-focusing by a combination of beams in the same heat affected zone [HAZ]
• • 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
  • B23K26/064—Shaping the laser beam, e.g. by masks or multi-focusing by means of optical elements, e.g. lenses, mirrors or prisms
  • B23K26/0648—Shaping the laser beam, e.g. by masks or multi-focusing by means of optical elements, e.g. lenses, mirrors or prisms comprising 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
  • 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
  • B23K26/067—Dividing the beam into multiple beams, e.g. multifocusing
  • B23K26/0676—Dividing the beam into multiple beams, e.g. multifocusing into dependently operating sub-beams, e.g. an array of spots with fixed spatial relationship or for performing simultaneously identical operations
• • 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
• • 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
  • B23K26/08—Devices involving relative movement between laser beam and workpiece
  • B23K26/0869—Devices involving movement of the laser head in at least one axial direction
• • 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
  • B23K26/50—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
• • 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
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B33/00—Severing cooled glass
  • C03B33/10—Glass-cutting tools, e.g. scoring tools
  • C03B33/102—Glass-cutting tools, e.g. scoring tools involving a focussed radiation beam, e.g. lasers
• • 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
  • B23K2103/54—Glass

Definitions

• the present specification generally relates to apparatuses and methods for laser processing transparent workpieces, and more particularly, to forming contour lines in transparent workpieces for separating transparent workpieces.
• the area of laser processing of materials encompasses a wide variety of applications that involve cutting, drilling, milling, welding, melting, etc. of different types of materials.
• these processes one that is of particular interest is cutting or separating different types of transparent substrates in a process that may be utilized in the production of materials such as glass, sapphire, or fused silica for thin film transistors (TFT) or display materials for electronic devices.
• TFT thin film transistors
• a method for laser processing a transparent workpiece includes forming a contour line in the transparent workpiece, the contour line including defects in the transparent workpiece.
• Forming the contour line includes directing a pulsed laser beam oriented along a beam pathway and output by a beam source through an aspheric optical element positioned offset in a radial direction from the beam pathway and into the transparent workpiece such that the portion of the pulsed laser beam directed into the transparent workpiece generates an induced absorption within the transparent workpiece.
• the induced absorption produces a defect within the transparent workpiece and the portion of the pulsed laser beam directed into the transparent workpiece includes a wavelength ⁇ , an effective spot size and a non-axisymmetric beam cross section that comprises a
• a method for laser processing a transparent workpiece includes forming a contour line in the transparent workpiece, the contour line including defects in the transparent workpiece.
• Forming the contour line includes directing a pulsed laser beam oriented along a beam pathway and output by a beam source through an aspheric optical element, and beyond an optical blocking element, where the aspheric optical element and the optical blocking element are each positioned between the beam source and the transparent workpiece, and into the transparent workpiece, such that the portion of the pulsed laser beam directed into the transparent workpiece generates an induced absorption within the transparent workpiece.
• the induced absorption produces a defect within the transparent workpiece and the portion of the pulsed laser beam directed into the transparent workpiece includes a wavelength ⁇ , an effective spot size and a non-axisymmetric cross section
• a method for laser processing a transparent workpiece includes forming a contour line in the transparent workpiece, the contour line including defects in the transparent workpiece.
• Forming the contour line includes directing a pulsed laser beam oriented along a beam pathway and output by a beam source through an aspheric optical element, decohering a first beam portion of the pulsed laser beam from a second beam portion of the pulsed laser beam using a decohering optical element positioned between the beam source and the transparent workpiece, and directing the first beam portion and the second beam portion of the pulsed laser beam into the transparent workpiece, such that the first beam portion and the second beam portion of the pulsed laser beam directed into the transparent workpiece generate an induced absorption within the transparent workpiece.
• the induced absorption produces a defect within the transparent workpiece and a combination of the first beam portion and the second beam portion directed into the transparent workpiece includes a wavelength ⁇ , an effective spot size w o ej y, and a non-axisymmetric cross section that comprises a minimum Rayleigh range in a cross-sectional x-direction and a
• a processing method includes localizing a pulsed laser beam in a transparent workpiece, the pulsed laser beam propagating in a z-direction and including (i) a wavelength ⁇ ; (ii) an effective spot size w o ej y; (iii) a pulse energy and pulse duration sufficient to exceed a damage threshold of the transparent workpiece; (iv) a first portion and a second portion, the first portion being incoherent with respect to the second portion; and (v) a non-axisymmetric beam cross section with a minimum Rayleigh range Z Rx min in the x-direction and a minimum Rayleigh range Z Ry min in the y-direction. Further, the smaller of Z Rx min and Z Ry min is greater than is a dimensionless
• the method comprising; providing a transparent workpiece, directing a laser beam onto the workpiece to thereby form a contour line in the transparent workpiece, along which contour line the transparent workpiece is separable, wherein the laser beam is a pulsed laser beam emitted by a laser beam source, wherein the pulsed laser beam is localized in the transparent workpiece, the pulsed laser beam propagating along a beam pathway in a z direction, which pulsed laser beam has, a wavelength ⁇ ; a non-axisymmetric beam cross section; a maximum beam intensity; an effective spot size w o e jy, which effective spot size is defined as a shortest radial distance in any direction from the beam propagation pathway z at which beam intensity decreases to 1/e of the maximum beam intensity; a pulse energy and pulse duration sufficient to exceed a damage threshold of the transparent workpiece to thereby form the contour line in the transparent workpiece which contour line comprises a defect in the transparent work piece; wherein the non-axisymmetric beam cross section has a minimum Rayleigh range Z R
• the laser beam has a pulse energy and a pulse duration sufficient to exceed a damage threshold of the transparent workpiece the thereby form the contour line, which contour line comprises a defect in the transparent workpiece, and preferably further comprising translating the transparent workpiece and the pulsed laser beam relative to each other along the contour line, thereby laser forming a plurality of defects along the contour line within the transparent workpiece.
• the laser beam comprises a first portion and a second portion, the first portion being incoherent with respect to the second portion.
• the aspheric optical element is offset from the beam pathway in the radial direction by an offset distance
• the offset distance is a distance from about 10% to about 75% of a cross sectional diameter of the pulsed laser beam at a contact location between the pulsed laser beam and the aspheric optical element.
• the defect comprises a central defect region and at least one radial arm that extends outward from the central defect region along the long axis of the non-axisymmetric beam cross section of the pulsed laser beam directed into the transparent workpiece.
• the method according to any of the preceding clauses further comprising decohering a first beam portion of the laser beam from a second beam portion of the laser beam using a decohering optical element positioned between the beam source and the transparent workpiece, preferably wherein the decohering optical element is positioned between the aspheric optical element and the transparent workpiece, or between the beam source and the aspheric optical element.
• decohering optical element comprises an optical delay plate and decohering the first beam portion from the second beam portion comprises directing the first beam portion of the pulsed laser beam through the optical delay plate to induce optical retardation of the first beam portion relative to the second beam portion.
• decohering the first beam portion from the second beam portion comprises: polarizing the first beam portion of the pulsed laser beam such that the first beam portion of the pulsed laser beam comprises a first polarization at the transparent workpiece; and polarizing the second beam portion of the pulsed laser beam such that the second beam portion of the pulsed laser beam comprises a second polarization at the transparent workpiece, wherein the first polarization is orthogonal to the second polarization.
• a laser beam source for providing a pulsed laser beam, means for converting the laser beam provided from the source to a laser beam having a non-axisymmetric cross section, the non-axisymmetric laser beam having a wavelength ⁇ ; a maximum beam intensity; an effective spot size which effective spot size is defined as a shortest radial
• the non-axisymmetric beam cross section has a minimum Rayleigh range in the x-direction and a minimum Rayleigh rang in the y-direction
• dimensionless divergence factor having a value of 10 or greater, and wherein the smaller of the minimum Rayleigh ranges in the x and y direction is the distance along the beam pathway at which the optical intensity of the beam decays to one half of the maximum beam intensity.
• System according to clause 12 further comprising means for converting the laser beam to a quasi non-diffracting laser beam.
• the means for converting the laser beam to a quasi non-diffracting laser beam include, an aspheric element, preferably an axicon lens, offset relative to the beam propagation pathway and a beam decohering element.
• a second, preferably, rotatable split quarter wave plate for creating a polarization based decoherence of two sections of the laser beam, and a focusing lens for focusing the laser beam on the transparent workpiece
• FIG. 1A schematically depicts the formation of a contour line of defects, according to one or more embodiments described herein;
• FIG. IB schematically depicts an example pulsed laser beam focal line during processing of a transparent workpiece, according to one or more embodiments described herein;
• FIG. 2 schematically depicts a non-axisymmetric beam spot traversing a line of desired separation to form a contour line in a transparent workpiece, according to one or more embodiments described herein;
• FIG. 3 schematically depicts a conventional embodiment of an optical assembly for pulsed laser processing, according to one or more embodiments described herein;
• FIG. 4 schematically depicts an embodiment of an optical assembly for pulsed laser processing comprising an offset aspheric optical element, according to one or more embodiments described herein;
• FIG. 5A schematically depicts an embodiment of an optical assembly for pulsed laser processing comprising an optical blocking element, according to one or more embodiments described herein;
• FIG. 5B schematically depicts an embodiment of an optical assembly for pulsed laser processing comprising two optical blocking elements, according to one or more embodiments described herein;
• FIG. 6 schematically depicts an embodiment of an optical assembly for pulsed laser processing comprising an optical delay plate, according to one or more embodiments described herein;
• FIG. 7A schematically depicts an embodiment of an optical assembly for pulsed laser processing comprising a split quarter waveplate, according to one or more embodiments described herein;
• FIG. 7B schematically depicts the split quarter waveplate of FIG. 7A, according to one or more embodiments described herein;
• FIG. 7C graphically depicts the relative intensity of laser pulses within an exemplary pulse burst vs. time, according to one or more embodiments described herein, according to one or more embodiments described herein;
• FIG. 7D graphically depicts relative intensity of laser pulses vs. time within another exemplary pulse burst, according to one or more embodiments described herein;
• FIG. 8A depicts a cross-sectional intensity plot of an example pulsed laser beam, according to one or more embodiments described herein;
• FIG. 8B depicts a logarithmic intensity plot of a Fourier transform plane of an example pulsed laser beam, according to one or more embodiments described herein;
• FIG. 8C depicts a near-field micrograph of an example pulsed laser beam, according to one or more embodiments described herein;
• FIG. 9 depicts a cross-sectional intensity plot of an example pulsed laser beam, according to one or more embodiments described herein;
• FIG. 10 depicts a cross- sectional intensity plot of an example pulsed laser beam, according to one or more embodiments described herein;
• FIG. 11A depicts a two-dimensional cross-sectional intensity plot of an example pulsed laser beam, according to one or more embodiments described herein;
• FIG. 11B depicts a set of one-dimensional horizontal and vertical line cross sections of the two-dimensional cross-sectional intensity plot of FIG. 11 A, according to one or more embodiments described herein;
• FIG. l lC depicts another set of one-dimensional horizontal and vertical line cross sections of the two-dimensional cross-sectional intensity plot of FIG. 11 A, according to one or more embodiments described herein;
• FIG. 11D depicts a logarithmic intensity plot of a Fourier transform plane of an example pulsed laser beam, according to one or more embodiments described herein;
• FIG. HE depicts a near-field micrograph of an example pulsed laser beam, according to one or more embodiments described herein;
• FIG. 12A depicts a cross-sectional intensity plot of an example pulsed laser beam, according to one or more embodiments described herein;
• FIG. 12B depicts a cross-sectional intensity plot of an example pulsed laser beam, according to one or more embodiments described herein;
• FIG. 12C depicts a cross-sectional intensity plot of an example pulsed laser beam, according to one or more embodiments described herein;
• FIG. 12D graphically depicts one-dimensional cross sections of the intensity plots of FIGS. 12A-12C, according to one or more embodiments described herein;
• FIG. 12E graphically depicts the Fourier transform of an example Sgn step function, accordingly to one or more embodiments described herein;
• FIG 12F depicts a cross-sectional intensity plot of an example pulsed laser beam, according to one or more embodiments described herein;
• FIG. 12G graphically depicts one-dimensional X and Y cross-sections of the two dimensional cross-sectional intensity plot of FIG. 12F, according to one or more embodiments described herein;
• FIG 12H depicts a cross-sectional intensity plot of an example pulsed laser beam, according to one or more embodiments described herein;
• FIG. 121 graphically depicts one-dimensional X and Y cross-sections of the two dimensional cross-sectional intensity plot of FIG. 12H, accordingly to one or more embodiments described herein;
• FIG. 13A depicts a cross-sectional intensity plot of an example pulsed laser beam, according to one or more embodiments described herein;
• FIG. 13B depicts a cross-sectional intensity plot of an example pulsed laser beam, according to one or more embodiments described herein;
• FIG. 13C depicts a cross-sectional intensity plot of an example pulsed laser beam, according to one or more embodiments described herein;
• FIG. 13D depicts a cross-sectional intensity plot of an example pulsed laser beam, according to one or more embodiments described herein;
• FIG. 13E depicts a cross-sectional intensity plot of an example pulsed laser beam, according to one or more embodiments described herein;
• FIG. 13F depicts a cross-sectional intensity plot of an example pulsed laser beam, according to one or more embodiments described herein;
• FIG. 13G depicts a cross-sectional intensity plot of an example pulsed laser beam, according to one or more embodiments described herein;
• FIG. 13H depicts a cross-sectional intensity plot of an example pulsed laser beam, according to one or more embodiments described herein;
• FIG. 131 depicts a cross-sectional intensity plot of an example pulsed laser beam, according to one or more embodiments described herein;
• FIG. 13J depicts a cross-sectional intensity plot of an example pulsed laser beam, according to one or more embodiments described herein;
• FIG. 13K depicts a cross-sectional intensity plot of an example pulsed laser beam, according to one or more embodiments described herein;
• FIG. 14 depicts a near-field micrograph of an example pulsed laser beam, according to one or more embodiments described herein;
• FIG. 15 depicts a near- field micrograph of an example pulsed laser beam, according to one or more embodiments described herein;
• FIG. 16 depicts example resultant non-axisymmetric beam spots formed by an optical blocking element positioned in an example optical assembly, according to one or more embodiments described herein;
• FIG. 17A depicts a cross-sectional intensity plot of an example pulsed laser beam, according to one or more embodiments described herein;
• FIG. 17B depicts a cross-sectional intensity plot of an example pulsed laser beam, according to one or more embodiments described herein;
• FIG. 17C depicts a cross-sectional intensity plot of an example pulsed laser beam, according to one or more embodiments described herein;
• FIG. 17D depicts a cross-sectional intensity plot of an example pulsed laser beam, according to one or more embodiments described herein;
• FIG. 17E depicts a cross-sectional intensity plot of an example pulsed laser beam, according to one or more embodiments described herein;
• FIG. 17F depicts a cross-sectional intensity plot of an example pulsed laser beam, according to one or more embodiments described herein;
• FIG. 18 depicts example resultant non-axisymmetric beam spots formed by two optical blocking elements positioned in an example optical assembly, according to one or more embodiments described herein;
• FIG. 19A depicts a cross sectional image of an example pulsed laser beam, according to one or more embodiments described herein;
• FIG. 19B depicts a cross-sectional intensity plot of an example pulsed laser beam, according to one or more embodiments described herein;
• FIG. 20A depicts a cross-sectional intensity plot of an example pulsed laser beam, according to one or more embodiments described herein;
• FIG. 20B graphically depicts one-dimensional X and Y cross sections of the two dimensional cross-sectional intensity plot of FIG. 20A, according to one or more embodiments described herein;
• FIG. 21A depicts a cross-sectional intensity plot of an example pulsed laser beam, according to one or more embodiments described herein;
• FIG. 21B graphically depicts one-dimensional X and Y cross sections of the two dimensional cross-sectional intensity plot of FIG. 21A, according to one or more embodiments described herein;
• FIG. 22A depicts a cross-sectional intensity plot of an example pulsed laser beam, according to one or more embodiments described herein;
• FIG. 22B graphically depicts one-dimensional X and Y cross sections of the two dimensional cross-sectional intensity plot of FIG. 22A, according to one or more embodiments described herein;
• FIG. 23 depicts example resultant non-axisymmetric beam spots formed by a split quarter waveplate positioned in an example optical assembly, according to one or more embodiments described herein.
• FIG. 24 depicts a Rayleigh range for a non-axisymmetric beam.
• FIG. 25 depicts an optical system for producing an asymmetric quasi non-diffracting beam.
• FIG. 26 depicts an optical system for producing an asymmetric quasi non-diffracting beam.
• FIG. 27 depicts a split quarter wave plate (SQWP).
• FIG. 28 shows schematically the production of an asymmetric QNDB using the polarization method to decohere the beam.
• FIG. 29 shows example images of nano-perforations and crack control.
• FIG. 30 shows a star pattern with nano -perforation lines at made at four different SQWP rotation angles.
• FIG. 31 shows an optical system for measuring the beam profile of a quasi-non- diffracting beam.
• FIG. 32 is an image of a beam cross section of a quasi-non-diffracting beam.
• FIG. 33 shows a plot of the peak intensity obtained from a series of x-y cross- sectional images measured at different focus positions along the optical axis.
• FIG. 34 shows an enlargement of the central portion of the beam cross section shown in Fig. 32.
• FIG. 35 shows an enlargement of the central portion of the beam cross section shown in Fig. 32.
• FIG. 36 shows intensity profiles in the x- and y-directions obtained from the beam cross section shown in Fig. 34.
• FIG. 37 is an image of a beam cross section of a quasi-non-diffracting beam.
• FIG. 38 shows a plot of the peak intensity obtained from a series of x-y cross- sectional images measured at different focus positions along the optical axis.
• FIG. 39 shows an enlargement of the central portion of the beam cross section shown in Fig. 37.
• FIG. 40 shows an enlargement of the central portion of the beam cross section shown in Fig. 37.
• FIG. 41 shows intensity profiles in the x- and y-directions obtained from the beam cross section shown in Fig. 37.
• FIG. 42 shows an xy cross section of an axisymmetric beam.
• FIG. 43 shows the intensity profile and variance of an axisymmetric beam.
• FIG. 44 shows an xy cross section of an asymmetric beam.
• FIG. 45 shows the intensity profile and variance of an asymmetric beam.
• a transparent workpiece may be laser processed to form a contour line in the transparent workpiece comprising a series of defects that define a line of intended separation of the transparent workpiece into two or more portions.
• a pulsed laser beam that projects a non-axisymmetric extended focal line having a beam cross section with a long axis and a short axis onto the transparent workpiece may be utilized to create a series of defects in the transparent workpiece thereby defining the contour line.
• defects may be referred to, in various embodiments herein, as line defects, perforations, or nano-perforations in the workpiece.
• these defects may include a central defect region and radial arms that primarily form along the long axis of the non- axisymmetric beam spot.
• the process may further include separating the transparent workpiece along the contour line, for example, using an infrared laser or other laser configured to heat the area of the transparent workpiece adjacent to the contour line or to bend, scribe, or otherwise mechanically stress the transparent workpiece.
• the transparent workpiece may be mechanically stressed to cause separation, or separation may occur spontaneously. While not intended to be limited by theory, stressing the transparent workpiece at the contour line may propagate a crack along the contour line. By controlling the direction of the radial arms of each defect along the contour line, the crack propagation may be better controlled.
• transparent workpiece means a workpiece formed from glass or glass-ceramic which is transparent, where the term “transparent,” as used herein, means that the material has an optical absorption of less than about 20% per mm of material depth, such as less than about 10% per mm of material depth for the specified pulsed laser wavelength, or such as less than about 1% per mm of material depth for the specified pulsed laser wavelength.
• the transparent workpiece may have a thickness of from about 50 microns to about 10 mm (such as from about 100 microns to about 5 mm, or from about 0.5 mm to about 3 mm).
• the present disclosure provides methods for processing workpieces.
• laser processing may include forming contour lines in workpieces, separating workpieces, or combinations thereof.
• Transparent workpieces may comprise glass workpieces formed from glass compositions, such as borosilicate glass, soda-lime glass, aluminosilicate glass, alkali aluminosilicate, alkaline earth aluminosilicate glass, alkaline earth boro-aluminosilicate glass, fused silica, or crystalline materials such as sapphire, silicon, gallium arsenide, or combinations thereof.
• the glass may be ion-exchangeable, such that the glass composition can undergo ion-exchange for mechanical strengthening before or after laser processing the transparent workpiece.
• the transparent workpiece may comprise ion exchanged and ion exchangeable glass, such as Corning Gorilla® Glass available from Corning Incorporated of Corning, NY (e.g., code 2318, code 2319, and code 2320).
• these ion exchanged glasses may have coefficients of thermal expansion (CTE) of from about 6 ppm/°C to about 10 ppm/°C.
• the glass composition of the transparent workpiece may include greater than about 1.0 mol.% boron and/or compounds containing boron, including, without limitation, B 2 O 3 .
• the glass compositions from which the transparent workpieces are formed include less than or equal to about 1.0 mol.% of oxides of boron and/or compounds containing boron.
• the transparent workpiece may comprise other components which are transparent to the wavelength of the laser, for example, crystals such as sapphire or zinc selenide.
• Some transparent workpieces may be utilized as display and/or TFT (thin film transistor) substrates.
• TFT thin film transistor
• Some examples of such glasses or glass compositions suitable for display or TFT use are EAGLE XG ® , CONTEGO, and CORNING LOTUSTM available from Corning Incorporated of Corning, NY.
• the alkaline earth boro-aluminosilicate glass compositions may be formulated to be suitable for use as substrates for electronic applications including, without limitation, substrates for TFTs.
• the glass compositions used in conjunction with TFTs typically have CTEs similar to that of silicon (such as less than 5 x 10 ⁇ 6 /K, or even less than 4 x 10 ⁇ 6 /K, for example, approximately 3 x 10 ⁇ 6 /K, or about 2.5 x 10 " 6 /K to about 3.5 x 10 ⁇ 6 /K), and have low levels of alkali within the glass.
• Low levels of alkali may be used in TFT applications because alkali dopants, under some conditions, leach out of glass and contaminate or "poison" the TFTs, possibly rendering the TFTs inoperable.
• the laser cutting processes described herein may be used to separate transparent workpieces in a controlled fashion with negligible debris, minimum defects, and low subsurface damage to the edges, preserving workpiece integrity and strength.
• contour line denotes a line (e.g., a line, a curve, etc.) formed along a desired line of separation on the surface of a transparent workpiece along which a transparent workpiece will be separated into multiple portions upon exposure to the appropriate processing conditions.
• the contour line generally consists of one or more defects introduced into the transparent workpiece using various techniques.
• a "defect” may include an area of modified material (relative to the bulk material), void space, scratch, flaw, hole, or other deformities in the transparent workpiece which enables separation by additional processing, such as by infrared laser processing, mechanical stress, or other separation processes.
• each defect may comprise a central defect region and one or more radial arms extending outward from the central defect region along an imaging surface of the transparent workpiece.
• imaging surface is the surface of the transparent workpiece at which the pulsed laser beam initially contacts the transparent workpiece.
• the radial length of the one or more radial arms may be controlled by the shape of a beam spot projected onto the transparent workpiece by a pulsed laser beam.
• a pulsed laser beam comprising a non-axisymmetric beam spot generally comprising a long axis and a short axis may irradiate the imaging plane of the transparent workpiece to generate defects that comprise a central defect region formed at the intersection of the long axis and the short axis of the non-axisymmetric beam spot and one or more radial arms formed in the direction of the long axis of the non-axisymmetric beam spot.
• a transparent workpiece such as a glass substrate or the like, may be separated into multiple portions by first forming a contour line on the surface of the workpiece and, thereafter, heating, for example, using an infrared laser, the surface of the workpiece on the contour line to create stresses in the workpiece, such as thermal stresses. The stresses ultimately lead to the spontaneous separation of the workpiece along the contour line. Further, when each defect is formed using a pulsed laser beam having a non-axisymmetric beam spot oriented such that the long axis of the beam axis extends along the desired line of separation, crack propagation caused by stressing defects in the transparent workpiece along the contour line may extend in the desired line of separation.
• Forming defects having radial arms that extend in the direction of the desired line of separation may allow the defects to be spaced apart at larger spacing distances than defects having randomly extending radial arms or no radial arms, without damage to the edges of the separated transparent workpieces where the contour line existed prior to separation.
• forming defects having radial arms that extend in the direction of the desired line of separation allows crack propagation to be generated by less stress, e.g., less energy, such as thermal energy, applied to the workpiece, limiting damage to the edges of the separated transparent workpieces where the contour line existed prior to separation.
• cracks may propagate from the separated edge in a direction generally perpendicular to the edge of the separated transparent workpiece (i.e., generally perpendicular to the intended line of separation denoted by the contour line) which weaken the edges of separated transparent workpiece.
• FIGS. 1A and IB a transparent workpiece 160, such as a glass workpiece or a glass-ceramic workpiece, is schematically depicted undergoing processing according to the methods described herein.
• FIGS. 1A and IB depict the formation of a contour line 170 in the transparent workpiece 160, which may be formed by translating a pulsed laser beam 112 relative to the transparent workpiece in a translation direction 101.
• FIGS. 1A and IB depict the pulsed laser beam 112 along a beam pathway 111 and oriented such that the pulsed laser beam 112 may be focused into a pulsed laser beam focal line 113 within the transparent workpiece 160 by a lens (e.g., a second lens 132 as described below).
• a lens e.g., a second lens 132 as described below.
• the pulsed laser beam focal line 113 is a portion of a quasi non- diffracting beam, as defined in more detail below.
• the pulsed laser beam focal line 113 is non- axisymmetric at cross sections of the pulsed laser beam focal line 113 normal to the propagation axis of the pulsed laser beam 112 (e.g., normal to the beam pathway 111).
• axisymmetric refers to a shape that is symmetric, or appears the same, for any arbitrary rotation angle made about a central axis
• non-axisymmetric refers to a shape that is not symmetric for any arbitrary rotation angle made about a central axis.
• the rotation axis e.g., the central axis
• beam spot refers to a cross section of a laser beam (e.g., the pulsed laser beam 112) at a point of first contact with a workpiece (e.g., the transparent workpiece 160).
• the contour line 170 extends along the desired line of separation 165 and delineates a line of intended separation about which the transparent workpiece 160 may be separated into two or more portions.
• the contour line 170 comprises a plurality of defects 172 that extend into the surface of the transparent workpiece 160 and establish a path for crack propagation for separation of the transparent workpiece 160 into separate portions along the contour line 170. While the contour line 170 is depicted in FIG. 1A and FIG. 2 as being substantially linear, it should be understood that other configurations are contemplated and possible including, without limitation, curves, patterns, regular geometric shapes, irregular shapes, and the like.
• each defect 172 includes a central defect region 174 and one or more radial arms 176 extending outward in a direction substantially perpendicular to the beam pathway 111 (e.g., in the X and/or Y directions as shown in FIGS. 1A, IB, and 2).
• the defects 172 may be further acted upon in a subsequent separating step to induce spontaneous separation of the transparent workpiece 160 along the contour line 170.
• the subsequent separating step may include using mechanical force, thermal stress induced force, or a spontaneous break occurring due to stress present in the transparent workpiece, depending on the type, thickness, and structure of the transparent workpiece 160.
• stress may be present in the transparent workpiece 160 which may cause spontaneous separation without further heating or mechanical separation steps.
• a pulsed laser beam 112 (with a non-axisymmetric beam spot 114 projected onto the transparent workpiece 160) may be directed onto the transparent workpiece 160 (e.g., condensed into a high aspect ratio line focus that penetrates through at least a portion of the thickness of the transparent workpiece 160).
• the pulsed laser beam focal line 113 having non- axisymmetric cross sections correlated with the non-axisymmetric beam spot 114.
• the non-axisymmetric beam spot 114 is an example cross section of the pulsed laser beam focal line 113 and the pulsed laser beam focal line 113 remains non-axisymmetric as the pulsed laser beam focal line 113 penetrates at least a portion of the transparent workpiece 160.
• the pulsed laser beam 112 may be translated relative to the transparent workpiece 160 (e.g., in the translation direction 101) to form the plurality of defects 172 of the contour line 170.
• the pulsed laser beam 112 into the transparent workpiece 160 causes portions of the transparent workpiece 160 to fracture, for example, depositing enough energy to break chemical bonds in the transparent workpiece 160 at spaced locations along the desired line of separation 165 to form the defects 172.
• the pulsed laser beam may be translated across the transparent workpiece 160 by motion of the transparent workpiece 160 (e.g., motion of a translation stage 190 coupled to the transparent workpiece 160), motion of the pulsed laser beam (e.g., motion of the pulsed laser beam focal line 113), or motion of both the transparent workpiece 160 and the pulsed laser beam focal line 113.
• the pulsed laser beam focal line 113 By translating the pulsed laser beam focal line 113 relative to the transparent workpiece 160, the plurality of defects 172 may be formed in the transparent workpiece 160.
• the non-axisymmetric beam spot 114 comprises a long axis 116, a short axis 115, an axis intersection 118, which may be positioned at the center of the non-axisymmetric beam spot 114, and a beam spot perimeter 119.
• the long axis 116 is defined as the axis of the non-axisymmetric beam spot 114 having the longest distance from center within the non-axisymmetric beam spot 114
• the short axis 115 is defined as the axis of the non-axisymmetric beam spot 114 having the shortest distance from center within the non-axisymmetric beam spot 114. While the non- axisymmetric beam spot 114 is depicted in FIG.
• non-axisymmetric beam spot 114 may comprise a collection of multiple beam spots.
• other cross sections of the pulsed laser beam focal line 113 within the transparent workpiece 160 are also non-axisymmetric and also comprise a short axis and a long axis, as described above with respect to the non-axisymmetric beam spot 114.
• the distance from center of the non-axisymmetric beam spot 114 along the long axis may comprise from about 0.25 ⁇ to about 20 ⁇ , such as from about 1 ⁇ m to about 10 ⁇ , from about 2 ⁇ m to about 8 ⁇ , or from about 3 ⁇ m to about 6 ⁇ . Further, the distance from center of the non-axisymmetric beam spot 114 along the short axis may comprises from about 0.01 ⁇ to about 10 ⁇ , from about 0.1 ⁇ to about 10 ⁇ , or from about 0.7 ⁇ to about 3 ⁇ .
• the distance from center of the non- axisymmetric beam spot 114 along the short axis may be from about 5% to about 95% of the distance from center of the non-axisymmetric beam spot 114 along the long axis, such as from about 10% to about 50%, from about 20% to about 45%, or from about 30% to about 40% of the distance from center of the non-axisymmetric beam spot 114 along the long axis.
• Methods for determining beam spot size are disclosed hereinbelow.
• the optical assemblies shown in FIG. IB and FIG. 3, when operated using a Gaussian beam laser having axial symmetry will form an optical beam at the transparent workpiece 160 known in the art as a Gauss-Bessel beam.
• a Gauss-Bessel beam is one form of a quasi-non-diffracting beam (defined in greater detail below).
• the beam may then be termed a non-axisymmetric Gauss-Bessel beam.
• the principles and effects described herein extend beyond beams having a Gauss- Bessel intensity profile and extend to non-axisymmetric quasi-non-diffracting laser beams in general.
• measuring the asymmetry in a quasi-non- diffracting beam cannot be done as simply as measuring the asymmetry of a more traditional Gaussian beam.
• quasi non-diffracting beams typically have transverse profiles that are oscillatory, as compared to Gaussian beams, which decay monotonically.
• the diameter of a Gaussian beam is typically defined by a 1/e drop in intensity.
• the intensity of a quasi-non-diffracting beam can fluctuate above and below a 1/e intensity threshold multiple times as a function of radial distance.
• defining the size of even a radially symmetric quasi-non-diffracting beam is challenging.
• asymmetric Gaussian beams are known in the art, they are most often discussed as being single spots, where the Gaussian beam may have a larger diameter in the x-direction than in the y-direction, for example.
• the cross section of the beam may not have a single monotonically decaying core or spot. In such a situation, the "long" or “short" cross sectional axes of the beam are not readily apparent, which makes defining how to measure the asymmetry of a beam even more difficult.
• the pulsed laser beam 112 used to form the defects 172 further has an intensity distribution I(X,Y,Z), where Z is the direction of propagation of the pulsed laser beam 112, and X and Y are directions orthogonal to the direction of propagation, as depicted in the figures.
• the X-direction and Y-direction may also be referred to as cross-sectional directions and the X-Y plane may be referred to as a cross-sectional plane.
• the intensity distribution of the pulsed laser beam 112 in a cross-sectional plane may be referred to as a cross-sectional intensity distribution.
• the non-axisymmetric beam spot 114 comprises a cross- sectional intensity distribution that is non-axisymmetric.
• the non-axisymmetric beam spot 114 may have a greater intensity and thereby a greater distribution of cumulated energy from the pulsed laser beam 112 in areas along the long axis 116 of the non- axisymmetric beam spot 114 than along the short axis 115 of the non-axisymmetric beam spot 114.
• the pulsed laser beam 112 may transfer more energy along the desired line of separation 165 than onto areas adjacent the desired line of separation 165, forming defects 172 comprising longer radial arms 176 extending along the desired line of separation 165 than radial arms 176 extending in directions not along the desired line of separation 165.
• "cumulated energy” refers to all energy transferred onto a particular area of the transparent workpiece 160 by the pulsed laser beam 112 as the pulsed laser beam 112 irradiates the transparent workpiece 160.
• the pulsed laser beam 112 at the non-axisymmetric beam spot 114 may comprise a quasi-non-diffracting beam, for example, a beam having low beam divergence as mathematically defined below, by propagating the pulsed laser beam 112 through a aspheric optical element 120, as described in more detail below with respect to the optical assemblies 100 depicted in FIGS. 3-7A.
• Beam divergence refers to the rate of enlargement of the beam cross section in the direction of beam propagation (i.e., the Z direction).
• beam cross section refers to the cross section of the pulsed laser beam 112 along a plane perpendicular to the direction of propagation of the pulsed laser beam 112, for example, along the X-Y plane.
• beam cross section is the beam spot (e.g., the non-axisymmetric beam spot 114) of the pulsed laser beam 112 projected onto the transparent workpiece 160.
• Diffraction is one factor that leads to divergence of pulsed laser beams 112.
• Other factors include focusing or defocusing caused by the optical systems forming the pulsed laser beams 112 or refraction and scattering at interfaces.
• Pulsed laser beams 112 for forming the defects 172 of the contour line 170 may have small, non-axisymmetric beam spots 114, with low divergence and weak diffraction.
• the divergence of the pulsed laser beam 112 is characterized by the Rayleigh range Z R , which is related to the variance ⁇ of the intensity distribution and beam propagation factor M of the pulsed laser beam 112.
• Variance is a measure of the width, in the cross-sectional (X-Y) plane, of the intensity distribution of the pulsed laser beam 112 as a function of position z in the direction of beam propagation.
• variance in the X-direction may differ from variance in the Y-direction.
• Equations (7) and (8) indicate that
• Equations (7) and (8) can be rewritten in terms of a beam propagation factor M 2 , where separate beam propagations factors M 2 and M l y 2 for the x-direction and the y-direction are defined as:
• the Rayleigh range corresponds to the distance (relative to the position of the beam waist as defined in Section 3.12 of ISO 11146-1:2005(E)) over which the variance of the laser beam doubles (relative to the variance at the position of the beam waist) and is a measure of the divergence of the cross sectional area of the laser beam.
• the Rayleigh range can also be observed as the distance along the beam axis at which the optical intensity decays to one half of its value observed at the beam waist location (location of maximum intensity).
• Laser beams with large Rayleigh ranges have low divergence and expand more slowly with distance in the direction of propagation than laser beams with small Rayleigh ranges.
• Beam cross section is characterized by shape and dimensions. As stated previously, it may be desired to project a beam spot onto the transparent workpiece 160 that is a non- axisymmetric beam spot 114.
• Example non-axisymmetric cross sections include elliptical cross sections.
• the dimensions of the beam cross section are characterized by a spot size of the beam. For a Gaussian beam, spot size is frequently defined as the radial extent at which the intensity of the beam decreases to 1/e of its maximum value, denoted in Equation (17) as wo.
• Beams with axisymmetric (i.e. rotationally symmetric around the beam propagation axis Z) cross sections can be characterized by a single dimension or spot size that is measured at the beam waist location as specified in Section 3.12 of ISO 11146- 1 :2005(E).
• Equation (17) shows that spot size is equal to w 0 , which from Equation (18) corresponds to .
• Spot size can be similarly defined for non-axisymmetric beam
• the lack of axial (i.e. arbitrary rotation angle) symmetry for a non-axisymmetric beam means that the results of a calculation of values of ⁇ 0 ⁇ and a 0y will depend on the choice of orientation of the x-axis and y-axis.
• the x-axis may be the long axis 116 of the non-axisymmetric beam spot 114 and the y-axis may be the short axis 115.
• the x-axis may be the short axis 115 and the y-axis may be the long axis 116.
• ISO 11146-1:2005(E) refers to these reference axes as the principal axes of the power density distribution (Section 3.3-3.5) and in the following discussion we will assume that the x and y axes are aligned with these principal axes. Further, an angle ⁇ about which the x-axis and y-axis may be rotated in the cross-sectional plane (e.g., an angle of the x-axis and y-axis relative to reference positions for the x-axis and y-axis, respectively) may be used to define minimum (w 0 min ) and maximum values (w 0 max ) of the spot size parameters for a non-axisymmetric beam:
• the magnitude of the axial asymmetry of the beam cross section can be
• an axisymmetric beam cross section has an aspect ratio of 1.0, while elliptical and other non-axisymmetric beam cross sections have aspect ratios greater than 1.0, for example, greater than 1.1, greater than 1.2, greater than 1.3, greater than 1.4, greater than 1.5, greater than 1.6, greater than 1.7, greater than 1.8, greater than 1.9, greater than 2.0, or the like
• the beam cross section influences the cross sectional shape of the defects 172 formed by the pulsed laser beam 112 in the transparent workpiece 160.
• Cross-sectional shape of the defects 172 refers to shape of the defects in the direction perpendicular to the direction of propagation of the pulsed laser beam 112. If, for example, a laser beam is normally incident to the imaging surface 162 of the transparent workpiece 160, the cross-sectional shape of the defect 172 corresponds to the shape of the defects 172 in the plane of the imaging surface 162, or in any plane parallel to the plane of the imaging surface 162 of the workpiece.
• a laser beam with a circular beam cross section forms a defect 172 with a circular shape and a laser beam with a non-circular beam cross section forms a defect 172 with a non-circular shape.
• Control of the beam cross section leads to more effective cutting, fewer defects, and higher edge strength in separated parts.
• Control of the beam cross section includes control of the spot size, cross-sectional shape, and orientation of the beam cross section.
• non-axisymmetric beam cross sections having a maximum spot size parameter w o max oriented along (or approximately along) the desired line of separation 165 improves cutting by directing crack orientation along the trajectory of cutting.
• stresses associated with the formation of damage regions are concentrated near the damage region, but with random orientations. The random stress orientations are believed to lead to fracture in directions away from the intended trajectory of cutting, manifested as micro cracks and other defects in separated parts.
• aspect ratios of the non-axisymmetric beam spot 114) used to form defects 172 may be greater than 1.1, greater than 1.3, greater than 1.5, greater than 2.0, greater than 2.5, greater than 3.0, greater than 3.5, greater than 4.0, greater than 5.0, greater than 7.5, greater than 10.0, in the range from 1.1 to 20.0, in the range from 1.2 to 15.0, in the range from 1.3 to 10.0, in the range from 1.3 to 7.5, in the range from 1.3 to 5.0, in the range from 1.5 to 7.5, in the range from 1.5 to 5.0, in the range from 1.5 to 3.0, in the range from 1.75 to 5.0, in the range from 2.0 to 4.0, or the like.
• a pulsed laser beam 112 having low divergence may be used.
• non-axisymmetric laser beams having low divergence may be utilized for forming defects 172.
• divergence can be characterized by the Rayleigh range.
• Rayleigh ranges for the principal axes X and Y are defined by Equations (15) and (16) for the x-direction and y-direction, respectively, where it can be shown that for any real beam,
• Rayleigh range is the same in the X-direction and Y-direction and is expressed, for a beam with a Gaussian intensity distribution, by Equation (22) or Equation (23).
• Low divergence correlates with large values of the Rayleigh range and weak diffraction of the laser beam.
• Beams with Gaussian intensity profiles may be less preferred for laser processing to form defects because, when focused to small enough spot sizes (such as spot sizes in the range of microns, such as about 1-5 microns or about 1-10 microns) to enable available laser pulse energies to modify materials such as glass, they are highly diffracting and diverge significantly over short propagation distances. To achieve low divergence, it is desirable to control or optimize the intensity distribution of the pulsed laser beam to reduce diffraction. Pulsed laser beams may be non-diffracting or weakly diffracting. Weakly diffracting laser beams include quasi-non-diffracting laser beams.
• Representative weakly diffracting laser beams include Bessel beams, Gauss-Bessel beams, Airy beams, Weber beams, and Mathieu beams.
• the Rayleigh ranges Z Rx and Z Ry are unequal. Equations (15) and (16) indicate that Z Rx and Z Ry depend on ⁇ 0 ⁇ and a Qy , respectively, and above we noted that the values of ⁇ 0 ⁇ and a 0y depend on the orientation of the X-axis and Y- axis.
• Z Rx and Z Ry will accordingly vary, and each will have a minimum value and a maximum value that correspond to the principal axes, with the minimum value of Z Rx being denoted as Z Rx rnin and the minimum value of Z Ry being denoted Z Ry rnin .
• Z Rx rnin the minimum value of Z Rx
• Z Ry rnin the minimum value of Z Ry
• the intensity distribution of the pulsed laser beam used for cutting may be controlled so that the minimum values of are as large as
• a laser beam with an intensity distribution may be used that makes the smaller o as large as possible when forming damage
• the smaller o is greater than or
• 50 ⁇ greater than or equal to 100 ⁇ , greater than or equal to 200 ⁇ , greater than or equal to 300 ⁇ m, greater than or equal to 500 ⁇ m, greater than or equal to 1 mm, greater than or equal to 2 mm, greater than or equal to 3 mm, greater than or equal to 5 mm, in the range from 50 ⁇ to 10 mm, in the range from 100 ⁇ to 5 mm, in the range from 200 ⁇ to 4 mm, in the range from 300 ⁇ to 2 mm, or the like.
• the spot size parameter w 0 min is greater than or equal to 0.25 ⁇ , greater than or equal to 0.50 ⁇ , greater than or equal to 0.75 ⁇ , greater than or equal to 1.0 ⁇ , greater than or equal to 2.0 ⁇ , greater than or equal to 3.0 ⁇ , greater than or equal to 5.0 ⁇ , in the range from 0.25 ⁇ to 10 ⁇ , in the range from 0.25 ⁇ to 5.0 ⁇ , in the range from 0.25 ⁇ to 2.5 ⁇ , in the range from 0.50 ⁇ to 10 ⁇ , in the range from 0.50 ⁇ to 5.0 ⁇ , in the range from 0.50 ⁇ to 2.5 ⁇ , in the range from 0.75 ⁇ to 10 ⁇ , in the range from 0.75 ⁇ to 5.0 ⁇ , in the range from 0.75 ⁇ to 5.0 ⁇ , in the range from 0.75 ⁇
• the Rayleigh range of the laser beam used to form damage regions may be greater than the Rayleigh range of a Gaussian beam having the same wavelength. Accordingly, the ratio of the smaller of Z Rx min and Z Ry min to the Rayleigh range Z R of a Gaussian beam (as specified in either of Equations (22) or (23)), at a common wavelength ⁇ , may be greater than or equal to 2, greater than or equal to 5, greater than or equal to 10, greater than or equal to 25, greater than or equal to 50, greater than or equal to 100, greater than or equal to 250, greater than or equal to 500, greater than or equal to 1000, in the range from 2 to 1500, in the range from 5 to 1250, in the range from 10 to 1000, in the range from 25 to 1000, in the range from 100 to 1000, or the like.
• Non-diffracting or quasi non-diffracting beams generally have complicated intensity profiles, such as those that decrease non-monotonically vs. radius.
• a criterion for Rayleigh range based on the effective spot size w 0 ejj can be specified for non- diffracting or quasi non-diffracting beams for forming damage regions, as follows:
• F D is a dimensionless divergence factor having a value of at least 10, at least 50, at least 100, at least 250, at least 500, at least 1000, in the range from 10 to 2000, in the range from 50 to 1500, in the range from 100 to 1000.
• the Rayleigh range can also be determined by measuring the distance over which the peak intensity of the beam drops by a factor of 2, as detailed above. This is referred to herein as the intensity method for determining the Rayleigh range.
• the criterion for the Rayleigh range based on the effective spot size can also be specified non-diffracting or quasi non-diffracting beams
• the dimensionless divergence factor F D provides a criterion for determining whether or not a laser beam is quasi-non-diffracting.
• a laser beam is considered quasi-non-diffracting if the characteristics of the laser beam satisfy Equation (31) with a value of F D ⁇ 10. As the value of F D increases, the laser beam approaches a more nearly perfectly non-diffracting state.
• FIGS. 3-7A optical assemblies 100 for producing a pulsed laser beam 112 that is quasi non-diffracting (FIGS. 3-7A) and, in some embodiments, produce a non-axisymmetric beam spot 114 at the transparent workpiece 160 (FIGS. 4-7 A).
• FIG. 3 depicts a conventional optical assembly 100 for pulsed laser processing, for example, for producing a pulsed laser beam 112 that is quasi-non-diffracting.
• FIGS. 4-7A each depict optical assemblies 100 that comprise additional components and arrangements not present in FIG. 3, for forming the non-axisymmetric beam spot 114 at the transparent workpiece 160.
• the optical assemblies 100 of FIGS. 5A and 5B include one or more optical blocking elements 140 positioned in the beam pathway 111.
• the optical assemblies 100 of FIGS. 6 and 7A each comprise one or more decohering optical elements configured to decohere a first beam portion of the pulsed laser beam 112 from a second beam portion of the pulsed laser beam 112.
• decohering optical element of the optical assembly 100 of FIG. 6 comprises an optical delay plate 142 positioned in the beam pathway 111
• the decohering optical element of the optical assembly 100 of FIG. 7 A comprises a split quarter waveplate 150 (also depicted in FIG. 7B) positioned in the beam pathway 111.
• to "decohere" means to make a first portion of the pulsed laser beam incoherent with a second portion of the pulsed laser beam.
• FIGS. 3-7A comprise a beam source 110, the aspheric optical element 120 (e.g., an axicon lens), a first lens 130, and a second lens 132.
• the transparent workpiece 160 may be positioned such that the pulsed laser beam 112 output by the beam source 110 irradiates the transparent workpiece 160, for example, after traversing the aspheric optical element 120 and thereafter, both the first and second lens 130, 132.
• An optical axis 102 extends between the beam source 110 and the transparent workpiece 160 along the Z- axis.
• 3-7A may optionally comprise a dove prism 180 positioned between the aspheric optical element 120 and the transparent workpiece 160 in the beam pathway 111. While the dove prism 180 is depicted in FIGS. 5 A, 5B, and 6, it should be understood that any of the optical assemblies 100 described herein may comprise the dove prism 180. Further, rotation of the dove prism 180 about the optical axis 102 may rotate the beam cross section of the pulsed laser beam 112 (e.g., the non-axisymmetric beam spot 114). Rotation of the non-axisymmetric beam spot 114 facilitates orienting the long axis 116 of the non-axisymmetric beam spot 114 along the desired line of separation 165 of the transparent workpiece 160.
• the pulsed laser beam 112 e.g., the non-axisymmetric beam spot 114
• the beam source 110 may comprise any known or yet to be developed beam source 110 configured to output pulsed laser beams 112.
• the defects 172 of the contour line 170 are produced by interaction of the transparent workpiece 160 with the pulsed laser beam 112 output by the beam source 110.
• the beam source 110 may output a pulsed laser beam 112 comprising a wavelength of for example, 1064 nm, 1030 nm, 532 nm, 530 nm, 355 nm, 343 nm, or 266 nm, or 215 nm.
• the pulsed laser beam 112 used to form defects 172 in the transparent workpiece 160 may be well suited for materials that are transparent to the selected pulsed laser wavelength.
• Suitable laser wavelengths for forming defects 172 are wavelengths at which the combined losses of absorption and scattering by the transparent workpiece 160 are sufficiently low.
• the combined losses due to absorption and scattering by the transparent workpiece 160 at the wavelength are less than 20%/mm, or less than 15%/mm, or less than 10%/mm, or less than 5%/mm, or less than 1%/mm, where the dimension "/mm" means per millimeter of distance within the transparent workpiece 160 in the direction of propagation of the pulsed laser beam 112 (e.g., the Z direction).
• Representative wavelengths for many glass workpieces include fundamental and harmonic wavelengths of Nd 3+ (e.g.
• Nd 3+ :YAG or Nd 3+ :YV0 4 having fundamental wavelength near 1064 nm and higher order harmonic wavelengths near 532 nm, 355 nm, and 266 nm).
• Other wavelengths in the ultraviolet, visible, and infrared portions of the spectrum that satisfy the combined absorption and scattering loss requirement for a given substrate material can also be used.
• the pulsed laser beam 112 output by the beam source 110 may create multi-photon absorption (MPA) in the transparent workpiece 160.
• MPA is the simultaneous absorption of two or more photons of identical or different frequencies that excites a molecule from one state (usually the ground state) to a higher energy electronic state (i.e., ionization). The energy difference between the involved lower and upper states of the molecule is equal to the sum of the energies of the involved photons.
• MPA also called induced absorption, can be a second-order or third-order process (or higher order), for example, that is several orders of magnitude weaker than linear absorption.
• the perforation step that creates the contour line 170 may utilize the beam source 110 (e.g., an ultra-short pulse laser) in combination with the optics depicted and described below with respect to FIGS. 3A-7A, to project the non-axisymmetric beam spot 114 on the transparent workpiece 160 and generate the pulsed laser beam focal line 113 of FIG. IB.
• the beam source 110 e.g., an ultra-short pulse laser
• the pulsed laser beam focal line 113 comprises a quasi non-diffracting beam, such as a non- axisymmetric Gauss-Bessel beam, as defined above, to fully perforate the transparent workpiece 160 to form the series of defects 172 in the transparent workpiece 160.
• the pulse duration of the individual pulses is in a range of from about 1 picosecond to about 100 picoseconds, such as from about 5 picoseconds to about 20 picoseconds, and the repetition rate of the individual pulses may be in a range from about 1 kHz to 4 MHz, such as in a range from about 10 kHz to about 3 MHz, or from about 10 kHz to about 650 kHz.
• the pulses may be produced in pulse bursts 500 of two pulses 500A (e.g., sub-pulses) or more (such as, for example, 3 pulses, 4 pulses, 5 pulses, 10 pulses, 15 pulses, 20 pulses, or more per pulse burst, such as from 1 to 30 pulses per pulse burst 500, or from 5 to 20 pulses per pulse burst 500).
• two pulses 500A e.g., sub-pulses
• more such as, for example, 3 pulses, 4 pulses, 5 pulses, 10 pulses, 15 pulses, 20 pulses, or more per pulse burst, such as from 1 to 30 pulses per pulse burst 500, or from 5 to 20 pulses per pulse burst 500.
• the pulses 500A within the pulse burst 500 may be separated by a duration that is in a range from about 1 nsec to about 50 nsec, for example, from about 10 nsec to about 30 nsec, such as about 20 nsec. In other embodiments, the pulses 500A within the pulse burst 500 may be separated by a duration of up to 100 psec (for example, 0.1 psec, 5 psec, 10 psec, 15 psec, 18 psec, 20 psec, 22 psec, 25 psec, 30 psec, 50 psec, 75 psec, or any range therebetween). For a given laser, the time separation T p (FIG.
• each pulse 500A within a pulse burst 500 is separated in time from the subsequent pulse by approximately 20 nsec (50 MHz).
• the time between each pulse burst 500 may be from about 0.25 microseconds to about 1000 microseconds, e.g., from about 1 microsecond to about 10 microseconds, or from about 3 microseconds to about 8 microseconds.
• the time separation T b (FIG. 7D) is about 5 microseconds for the beam source 110 outputting a pulsed laser beam 112 comprising a burst repetition rate of about 200 kHz.
• the laser burst repetition rate may be in a range of from about 1 kHz to about 4 MHz.
• the laser burst repetition rates may be, for example, in a range of from about 10 kHz to 650 kHz.
• the time T b between the first pulse in each burst to the first pulse in the subsequent burst may be from about 0.25 microsecond (4 MHz burst repetition rate) to about 1000 microseconds (1 kHz burst repetition rate), for example from about 0.5 microseconds (2 MHz burst repetition rate) to about 40 microseconds (25 kHz burst repetition rate), or from about 2 microseconds (500 kHz burst repetition rate) to about 20 microseconds (50k Hz burst repetition rate).
• the exact timing, pulse duration, and burst repetition rate may vary depending on the laser design, but short pulses (T d ⁇ 20 psec and, in some embodiments, T d ⁇ 15 psec) of high intensity have been shown to work particularly well.
• the burst repetition rate may be in a range of from about 1 kHz to about 2 MHz, such as from about 1 kHz to about 200 kHz.
• Bursting or producing pulse bursts 500 is a type of laser operation where the emission of pulses 500 A is not in a uniform and steady stream but rather in tight clusters of pulse bursts 500.
• the pulse burst laser beam may have a wavelength selected based on the material of the transparent workpiece 160 being operated on such that the material of the transparent workpiece 160 is substantially transparent at the wavelength.
• the average laser power per burst measured at the material may be at least about 40 ⁇ per mm of thickness of material.
• the average laser power per burst may be from about 40 ⁇ / ⁇ to about 2500 ⁇ / ⁇ , or from about 500 ⁇ /mm to about 2250 ⁇ /mm.
• pulse bursts of from about 300 ⁇ to about 600 ⁇ may cut and/or separate the workpiece, which corresponds to an exemplary range of about 428 ⁇ / ⁇ to about 1200 ⁇ /mm (i.e., 300 ⁇ /0.7 mm for 0.7 mm EAGLE XG ® glass and 600 ⁇ /0.5 mm for a 0.5 mm EAGLE XG ® glass).
• the energy required to modify the transparent workpiece 160 may be described in terms of the burst energy (i.e., the energy contained within a pulse burst 500 where each pulse burst 500 contains a series of pulses 500A), or in terms of the energy contained within a single laser pulse (many of which may comprise a burst).
• the energy per pulse burst may be from about 25 ⁇ to about 750 ⁇ , e.g., from about 50 ⁇ to about 500 ⁇ , or from about 50 ⁇ to about 250 ⁇ .
• the energy per pulse burst may be from about 100 ⁇ to about 250 ⁇
• the energy per pulse burst may be higher (e.g., from about 300 ⁇ to about 500 ⁇ , or from about 400 ⁇ to about 600 ⁇ , depending on the specific glass composition of the transparent workpiece 160).
• the use of a pulsed laser beam 112 capable of generating such bursts is advantageous for cutting or modifying transparent materials, for example glass.
• the use of a burst sequence that spreads the laser energy over a rapid sequence of pulses within the burst allows access to larger timescales of high intensity interaction with the material than is possible with single-pulse lasers.
• the aspheric optical element 120 is positioned within the beam pathway 111 between the beam source 110 and the transparent workpiece 160.
• propagating the pulsed laser beam 112, e.g., an incoming Gaussian beam, through the aspheric optical element 120 may alter pulsed laser beam 112 such that the portion of the pulsed laser beam 112 propagating beyond the aspheric optical element 120 is quasi-non-diffracting, as described above.
• the aspheric optical element 120 may comprise any optical element comprising an aspherical shape.
• the aspheric optical element 120 may comprise a conical wavefront producing optical element, such as an axicon lens, for example, a negative refractive axicon lens, a positive refractive axicon lens, a reflective axicon lens, a diffractive axicon lens, a programmable spatial light modulator axicon lens (e.g., a phase axicon), or the like.
• a conical wavefront producing optical element such as an axicon lens, for example, a negative refractive axicon lens, a positive refractive axicon lens, a reflective axicon lens, a diffractive axicon lens, a programmable spatial light modulator axicon lens (e.g., a phase axicon), or the like.
• the aspheric optical element 120 comprises at least one aspheric surface whose shape is mathematically described
• At least one aspheric surface of the aspheric optical element 120 includes the following coefficients ⁇ ⁇ - ⁇ 7 , respectively: -0.085274788; 0.065748845; 0.077574995; - 0.054148636; 0.022077021; -0.0054987472; 0.0006682955; and the aspheric coefficients a 8 - a 12 are 0.
• the coefficient has a nonzero value, this is equivalent to having a conic
• an equivalent surface may be described by specifying a conic constant k that is non zero, a coefficient that is non-zero, or a
• the at least one aspheric surface is described or defined by at least one higher order aspheric coefficient with non-zero value (i.e., at least one of In one
• the aspheric optical element 120 comprises a third-order aspheric optical element such as a cubically shaped optical element, which comprises a coefficient a 3 that is non-zero.
• the axicon may have a laser output surface 126 (e.g., conical surface) having an angle of about 1.2°, such as from about 0.5° to about 5°, or from about 1° to about 1.5°, or even from about 0.5° to about 20°, the angle measured relative to the laser input surface 124 (e.g., flat surface) upon which the pulsed laser beam 112 enters the axicon lens. Further, the laser output surface 126 terminates at a conical tip. Moreover, the aspheric optical element 120 includes a centerline axis 122 extending from the laser input surface 124 to the laser output surface 126 and terminating at the conical tip.
• a laser output surface 126 e.g., conical surface
• the aspheric optical element 120 may comprise a waxicon, a spatial phase modulator such as a spatial light modulator, or a diffractive optical grating.
• the aspheric optical element 120 shapes the incoming pulsed laser beam 112 (e.g., an incoming Gaussian beam) into a quasi-non- diffracting beam, which, in turn, is directed through the first lens 130 and the second lens 132.
• the first lens 130 and the second lens 132 may collimate the pulsed laser beam 112 within a collimation space 134 between the first and second lens 130, 132. Further, the second lens 132 may focus the pulsed laser beam 112 into the transparent workpiece 160, which may be positioned at an imaging plane 104.
• the first lens 130 and the second lens 132 each comprise plano-convex lenses. When the first lens 130 and the second lens 132 each comprise plano-convex lenses, the curvature of the first lens 130 and the second lens 132 may each be oriented toward the collimation space 134.
• the first lens 130 may comprise other collimating lenses and the second lens 132 may comprise a meniscus lens, an asphere, or another higher-order corrected focusing lens.
• the first lens 130 comprises a first focal length Fi and the second lens 132 comprises a second focal length F 2 .
• focal length is defined as the distance between the lens and the focal point of the lens.
• the first focal length Fi and second focal length F 2 may be equal.
• the first focal length Fi and the second focal length F 2 may be different, for example, the second focal length F 2 may be less than the first focal length Fi or alternatively may be greater than the second focal length F 2 .
• the first and second lens 130, 132 may have focal lengths Fi, F 2 .
• the first lens 130 may be spaced from the second lens 132 by the sum of the first focal length Fi and the second focal length F 2 such that a common focal plane 105 is positioned in the collimation space 134 between the first lens 130 and the second lens 132.
• the common focal plane 105 is a location along the beam pathway 111 between the first lens 130 and the second lens 132 spaced a first focal length Fi downstream from the first lens 130 and spaced a second focal length F 2 upstream from the second lens 132.
• upstream and downstream refer to the relative position of two locations or components along the beam pathway 111 with respect to the beam source 110.
• a first component is upstream from a second component if the pulsed laser beam 112 traverses the first component before traversing the second component. Further, a first component is downstream from a second component if the pulsed laser beam 112 traverses the second component before traversing the first component.
• an embodiment of the optical assembly 100 comprising the aspheric optical element 120 positioned offset relative to the beam pathway 111 of the pulsed laser beam 112 in a radial direction (e.g., a direction along a radius of the pulsed laser beam 112, orthogonal to the beam propagation direction).
• a radial direction e.g., a direction along a radius of the pulsed laser beam 112, orthogonal to the beam propagation direction.
• the resultant beam spot projected onto the transparent workpiece 160 may comprise the non-axisymmetric beam spot 114 depicted in FIG. 2.
• the aspheric optical element 120 may be positioned offset from the beam pathway 111 (e.g., offset in the X-Y plane) by an offset distance a.
• the offset distance a is the distance in the X-Y plane between the centerline axis 122 of the aspheric optical element 120 and the cross-sectional center of the pulsed laser beam as the pulsed laser beam irradiates the laser input surface 124 of the aspheric optical element 120.
• the relative offset between the aspheric optical element 120 and the beam pathway may be achieved by shifting the aspheric optical element 120 along the X-Y plane, shifting the beam source 110 along the X-Y plane, or both.
• the magnitude of the offset required to sufficiently break the symmetry of the resulting beam spot is a function of the diameter of the pulsed laser beam 112, with smaller input laser beam diameters requiring less offset to sufficiently break the symmetry.
• the offset distance a may comprise from about 10 microns to about 500 microns, for example, 20 microns, 50 microns, 100 microns, 250 microns, or the like. In some embodiments, the offset distance a may be from about 20 microns to about 100 microns, or from about 50 microns to about 100 microns, or the like. In some embodiments, the offset distance may comprise a distance from about 10% to about 75% of a cross sectional diameter of the pulsed laser beam 112 at a contact location between the pulsed laser beam 112 and the aspheric optical element 120 (e.g., at the laser input surface 124 of the aspheric optical element 120).
• the resultant pulsed laser beam 112 may comprise a decreased overall intensity, for example, by a factor of about 4. Further the cross section of the pulsed laser beam 112 may broaden in the X-direction, the Y-direction, or a combination thereof in the X-Y plane by a factor of from about 1.2 to about 2, for example, 1.4, 1.6, 1.8, or the like. Broadening the cross section of the pulsed laser beam 112 forms the non-axisymmetric beam spot 114 having the long axis 116 in the direction of broadening.
• the resultant pulsed laser beam 112 may comprise a non- axisymmetric cone of rays, which form a non-axisymmetric ring in the collimation space 134 after traversing the first lens 130. Further, the cross section of the pulsed laser beam 112 (e.g., the non-axisymmetric beam spot 114) may be rotated by rotating the aspheric optical element 120 about the optical axis 102.
• optical blocking elements 140 e.g., opaque optical elements
• the optical blocking elements 140 may comprise an opaque plate which may further comprise an aperture.
• the optical blocking elements 140 may comprise a metal plate, or other substance that can withstand the energy of the pulsed laser beam 112 without breaking or being damaged.
• the optical blocking element 140 may be positioned in the beam pathway 111 such that the optical blocking element 140 blocks from about 5% to about 95% of the beam intensity of the pulsed laser beam 112, for example, at least about 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 85%, 90%, or the like. As one example, the optical blocking element 140 blocks from about 25% to about 80% of the beam intensity of the pulsed laser beam 112. Blocking a larger percentage of the beam intensity of the pulsed laser beam 112 increases the length of the long axis 116 of the non-axisymmetric beam spot 114 relative to the length of the short axis 115 of the non-axisymmetric beam spot 114. However, blocking a larger percentage of the beam intensity of the pulsed laser beam 112 increases the amount of power in the pulsed laser beam 112 lost at the optical blocking element 140.
• the optical blocking element 140 may block a cross sectional sector of the pulsed laser beam 112 (i.e., a sector defined by an azimuthal angle range or "pie slice" of the pulsed laser beam 112 that extends from a central location of the pulsed laser beam 112 to the outermost diameter of the pulsed laser beam 112).
• An optical blocking element 140 in the form of a sector has the advantage that equal percentages of the rays at all radii in the pulsed laser beam 112 are blocked.
• the optics map rays of specific radii to corresponding specific locations along the pulsed laser beam focal line 113. In the example embodiment depicted in FIGS.
• the lower radius rays in the vicinity of the aspheric optical element 120 will be mapped to locations at the upstream end of the pulsed laser beam focal line 113, and the higher radius rays in the vicinity of the aspheric optical element 120 will be mapped to locations near the downstream end of the pulsed laser beam focal line 113. If the optical blocking element 140 cuts out a larger fraction of rays at small radii than at large radii, then the magnitude or aspect ratio of the ellipticity of the cross sections of pulsed laser beam focal line 113 (the non-axisymmetric beam spot 114, as one example) will change throughout its length.
• the optical blocking element 140 may block a cross sectional chord portion of the pulsed laser beam 112, wherein the cross-sectional chord portion of the pulsed laser beam 112 is bounded by a portion of the cross sectional circumference of the pulsed laser beam 112 and an arbitrary cross-sectional chord of the pulsed laser beam 112. Further, in this example embodiment, a portion of the optical blocking element 140 that is positioned in the beam pathway 111 is coterminous with the arbitrary cross-sectional chord. Moreover, it should be understood that the optical blocking element 140 may block any arbitrary cross sectional portion of the pulsed laser beam 112.
• the optical blocking element 140 may be positioned between the beam source 110 and the transparent workpiece 160. Because the optical blocking element 140 is positioned between the beam source 110 and the transparent workpiece 160, in operation, the pulsed laser beam 112 will travel through the aspheric optical element 120 and beyond the optical blocking element 140 (e.g., an unblocked portion of the pulsed laser beam 112 will travel beyond the optical blocking element 140 but the blocked portion of the pulsed laser beam 112 not travel beyond the optical blocking element 140). Further, the pulsed laser beam 112 will travel through the aspheric optical element 120 and beyond the optical blocking element 140 regardless of the relative order of positioning of the aspheric optical element 120 and the optical blocking element 140 along the direction of beam propagation (e.g., the Z-direction).
• the pulsed laser beam 112 will travel through the aspheric optical element 120 and beyond the optical blocking element 140 regardless of the relative order of positioning of the aspheric optical element 120 and the optical blocking element 140 along the direction of beam propagation (e.g., the Z-direction).
• the optical blocking element 140 may be positioned upstream from the aspheric optical element 120, such that the optical blocking element 140 is positioned between the beam source 110 and the aspheric optical element 120. Further, the optical blocking element 140 may be positioned downstream from the aspheric optical element 120, such that the optical blocking element 140 is positioned between the aspheric optical element 120 and the transparent workpiece 160.
• the optical blocking element 140 may be positioned in the collimation space 134 between the first and second lens 130, 132, for example, at the common focal plane 105. Further, the cross-section of the pulsed laser beam focal line 113 (e.g., the non-axisymmetric beam spot 114) may be rotated by rotating the optical blocking element 140 about the optical axis 102. In some embodiments, the non-axisymmetric beam spot 114 may be formed by both offsetting the aspheric optical element 120 relative to the beam pathway 111 and blocking a portion of the pulsed laser beam 112 with the optical blocking element 140.
• this combination of offsetting and blocking may lower the amount of power loss caused by the optical blocking element 140 while still ensuring that the elliptical or otherwise non-axisymmetric beam spot 114 is generated and projected onto the transparent workpiece 160.
• the optical assembly 100 may comprise a first optical blocking element 140a and a second optical blocking element 140b.
• the first optical blocking element 140a is positioned in the beam pathway 111 at a first blocking location 141a and the second optical blocking element is positioned in the beam pathway 111 at a second blocking location 141b.
• the first optical blocking element 140a and the second optical blocking element 140b may be positioned such that they each block a portion of the beam pathway 111, for example, different portions of the beam pathway 111.
• the first optical blocking element 140a and the second optical blocking element 140b may each block different cross section segments of the pulsed laser beam 112.
• the optical blocking element 140a, 140b may define cross sectional chord portions of each blocked cross sectional segment that are positioned in parallel such that they block opposite sides of the cross section of the pulsed laser beam 112.
• the optical blocking element 140a, 140b may define different sectors of a circle, such that they block opposite sides of the cross section of the pulsed laser beam 112.
• the first and second blocking locations 141a, 141b are positioned at the same Z-axis location along the optical axis 102, as depicted in FIG. 5B. In other embodiments, the first and second blocking locations 141a 141b may be different locations along optical axis 102. Further, the first and second optical blocking elements 140a, 140b may collectively block from about 5% to about 75% of the intensity of the pulsed laser beam 112. Further, the first and second first and second optical blocking elements 140a, 140b may block equivalent percentages of the intensity of the pulsed laser beam 112 or different percentages of the intensity of the pulsed laser beam 112.
• blocking locations 141, 141a, 141b in FIGS. 5A and 5B are each depicted between the beam source 110 and the aspheric optical element 120, it should be understood that the blocking locations 141, 141a, 141b may be any location between the beam source 110 and the and the transparent workpiece 160, for example, between the first lens 130 and the second lens 132, for example, at the common focal plane 105.
• blocking the pulsed laser beam 112 with multiple (e.g., two) optical blocking elements 140 may project multiple beam spots onto the imaging surface 162 of the transparent workpiece shaped such that the multiple beam spots collectively defining the non-axisymmetric beam spot 114 at the transparent workpiece 160, as depicted in FIG. 2.
• FIG. 6 an example embodiment of the optical assembly 100 is depicted comprising one or more optical delay plates 142 positioned between the beam source 110 and the transparent workpiece 160.
• positioning the optical delay plate 142 in the beam pathway 111 may form the non-axisymmetric beam spot 114 depicted in FIG. 2 by inducing an optical delay within a portion of the pulsed laser beam 112 to decohere a first beam portion of the pulsed laser beam 112 from a second beam portion by directing the first portion of the pulsed laser beam 112 through the optical delay plate to induce optical retardation of the first beam portion.
• the optical delay plate 142 may be positioned within the beam pathway 111 such that about 50% of the pulsed laser beam 112 (e.g., about 50% of the intensity of the pulsed laser beam 112) traverses the optical delay plate 142. While not intending to be limited by theory, the optical delay over half the pulsed laser beam 112 may form two beams collectively defining a non-axisymmetric beam spot 114 at the transparent workpiece 160. Further, the cross section of the pulsed laser beam 112 (e.g., the non-axisymmetric beam spot 114) may be rotated by rotating the optical delay plate 142 about the optical axis 102. Further, the optical delay plate 142 may be positioned upstream or downstream the aspheric optical element 120. For example, in some embodiments the optical delay plate 142 is positioned between the aspheric optical element 120 and the transparent workpiece 160 and in other embodiments, the optical delay plate 142 is positioned between the beam source 110 and the aspheric optical element 120.
• Optically delaying a portion (for example, one half) of the pulsed laser beam 112 may form a single non-axisymmetric beam spot 114 if the portion of the beam that traverses the optical delay plate 142 and the portion of the beam that does not traverse the optical delay plate 142 combine incoherently.
• the coherence length of the pulsed laser beam 112 may be shorter than the optical thickness of the optical delay plate 142.
• the optical delay of the two beams need not be set to any exact amount or controlled precisely; the optical delay may only be greater than the coherence time of the laser pulse. This is substantially equivalent to randomizing the optical phase difference between the two portions of the laser beam.
• the coherence time T c of an individual laser pulse may be calculated using methods known in the art, and is mathematically described as where ⁇ is the wavelength of the radiation, c is the speed of light, and ⁇ is the
• the thickness difference supplied by the optical delay plate 142 may be greater than the coherence time of the laser pulse, or equivalently, thicker than the coherence length of the laser pulse in the plate, which is mathematically described where n is the refractive index of the material of the optical delay plate 142
• the exact coherence time and coherence length are functions of the exact temporal and spectral shapes of the laser pulses, and as such, the formulas above are approximations.
• thickness may be slightly less than the values calculated by the above formulas (e.g. about 10% less , about 25% less , about 50% less, or the like).
• the optical delay plate 142 may be configured to induce a specific optical delay, for example, the optical delay plate 142 may induce an optical retardation of ⁇ over half the pulsed laser beam 112 (where one optical period of the laser wavelength is considered to cover 2 ⁇ radians of optical phase, so an optical retardation of ⁇ is a delay of one-half the optical period), an optical retardation of 0.875 ⁇ over half the pulsed laser beam 112, and, in some embodiments, an optical retardation of 0.5 ⁇ over half the laser beam.
• the exact profile of the intensity cross section of the beam can be altered from that of two equal high intensity spots near the center of the beam, to having one spot with more intensity and the other with less intensity near the center of the beam, to other more complex interference patterns, simply by adjusting the precise optical phase delay between the two portions of the beam.
• the specific optical retardation induced by the optical delay plate 142 is correlated with the optical thickness of the optical delay plate 142.
• the resultant beam spot is sensitive to exact optical path lengths of the two beam portions, which can be altered by environmental changes such as temperature and humidity.
• such a multi-spot pattern has a complex multi-axis stress concentration, which is may not as useful a stress concentration for controlling crack formation as would a beam with an elliptical core.
• the split quarter waveplate 150 comprises a first plate portion 152 having a first fast axis 156a and a first slow axis 158a.
• the split quarter waveplate 150 also comprises and a second plate portion 154 having a second fast axis 156b and a second slow axis 158b.
• the first fast axis 156a is orthogonal to the second fast axis 156b and the first slow axis 158a is orthogonal to the second slow axis 158b.
• the first plate portion 152 having the first fast axis 156a and first slow axis 158a polarizes a first beam portion of the pulsed laser beam 112 into a first polarization (e.g., a specific horizontal, vertical, or circular polarization) and the second plate portion 154 having the second fast axis 156b polarizes a second beam portion of the pulsed laser beam 112 into a second polarization (e.g., another specific horizontal, vertical, or circular polarization).
• Polarizing the first beam portion to a first polarization and polarizing the second beam portion to a second polarization that is orthogonal the second beam portion decoheres the first beam portion from the second beam portion.
• the first polarization is orthogonal to the second polarization such that the first beam portion and the second beam portion combine incoherently downstream from the split quarter waveplate 150 to form the non-axisymmetric beam spot 114 depicted in FIG. 2.
• two pulsed laser beam portions having orthogonal polarizations e.g., vertical and horizontal, right-handed circular and left-handed circular
• each beam portion combines incoherently and collectively form the non-axisymmetric beam spot 114 (e.g., an ellipse).
• the first polarization and the second polarization each comprise a location on a Poincare Sphere positioned apart by about 90° such that they are orthogonal. It should be understood that incoherent combination between the first and second beam portions may occur with any two orthogonal polarizations.
• the optical assembly 100 may further comprise a polarizer 144 and a quarter waveplate 146.
• the polarizer 144 and the quarter waveplate 146 are each positioned in the beam pathway 111 between the beam source 110 and the split quarter waveplate 150 such that the pulsed laser beam 112 traverses the polarizer 144 and the quarter waveplate 146 prior to traversing the split quarter waveplate 150.
• the polarizer 144 may filter (e.g., prevent) one or more specific polarizations from traversing the polarizer 144.
• the quarter waveplate 146 may polarize the pulsed laser beam 112 into a single polarization such that the pulsed laser beam 112 comprises a single polarization, such as right-handed circular polarization, or left-handed circular polarization, when the pulsed laser beam 112 reaches the split quarter waveplate 150.
• the split quarter waveplate 150 is positioned in the beam pathway 111 between the quarter waveplate 146 and the transparent workpiece 160.
• the split quarter waveplate 150 may be positioned upstream or downstream the aspheric optical element 120.
• the split quarter waveplate 150 is positioned between the aspheric optical element 120 and the transparent workpiece 160, and in other embodiments, the split quarter waveplate 150 is positioned between the beam source 110 and the aspheric optical element 120.
• the split quarter waveplate 150 may be positioned in the collimation space 134 between the first lens 130 and the second lens 132, for example, positioned at the common focal plane 105, such that a minimal amount of power in the pulsed laser beam 112 is lost due to interaction at the contact location between the first plate portion 152 and the second plate portion 154 of the split quarter waveplate 150.
• split quarter waveplate 150 is depicted as comprising two plate portions (e.g., the first and second plate portions 152, 154), other embodiments of the split quarter waveplate 150 may comprise any number of plate portions. As with the previously described blocking elements, these portions of the spilt quarter waveplate 150 may be made in the form of cross sectional chord portions, or more preferably sectors. In these embodiments, a first plurality of plate portions comprise the first fast axis 156a and the first slow axis 158a and a second plurality of plate portions comprise the second fast axis 156b and the second slow axis 158b.
• a method for forming the contour line 170 comprising defects 172 along the desired line of separation 165 includes directing (e.g., localizing) a pulsed laser beam 112 oriented along the beam pathway 111 and output by the beam source 110 into the transparent workpiece 160 such that the portion of the pulsed laser beam 112 directed into the transparent workpiece 160 generates an induced absorption within the transparent workpiece and the induced absorption produces a defect 172 within the transparent workpiece 160.
• the pulsed laser beam 112 may comprise a pulse energy and a pulse duration sufficient to exceed a damage threshold of the transparent workpiece 160.
• directing the pulsed laser beam 112 into the transparent workpiece 160 comprises focusing the pulsed laser beam 112 from output by the beam source 110 into a pulsed laser beam focal line 113 oriented along the beam propagation direction (e.g., the Z axis).
• the transparent workpiece 160 is positioned in the beam pathway 111 to at least partially overlap the pulsed laser beam focal line 113 of pulsed laser beam 112. The pulsed laser beam focal line 113 is thus directed into the transparent workpiece 160.
• the pulsed laser beam 112, e.g., the pulsed laser beam focal line 113 generates induced absorption within the transparent workpiece 160 to create the defect 172 in the transparent workpiece 160.
• the first lens 130 and/or the second lens 132 may focus the pulsed laser beam 112.
• the aspheric optical element 120 e.g., an axicon lens
• individual defects 172 may be created at rates of several hundred kilohertz (i.e., several hundred thousand defects per second).
• the position of pulsed laser beam focal line 113 may be controlled by suitably positioning and/or aligning the pulsed laser beam 112 relative to the transparent workpiece 160 as well as by suitably selecting the parameters of the optical assembly 100. Further, the pulsed laser beam focal line 113 may have a length in a range of from about 0.1 mm to about 100 mm or in a range of from about 0.1 mm to about 10 mm.
• Various embodiments may be configured to have a pulsed laser beam focal line 113 with a length 1 of about 0.1 mm, about 0.2 mm, about 0.3 mm, about 0.4 mm, about 0.5 mm, about 0.7 mm, about 1 mm, about 2 mm, about 3 mm, about 4 mm, or about 5 mm e.g., from about 0.5 mm to about 5 mm.
• the method for forming the contour line 170 comprising defects 172 along the desired line of separation 165 may include translating the transparent workpiece 160 relative to the pulsed laser beam 112 (or the pulsed laser beam 112 may be translated relative to the transparent workpiece 160, for example, in a translation direction 101 depicted in FIGS. 1A and 2) to form contour lines 170 that trace out the shape of a desired part with defects 172.
• the defects 172 that may penetrate the full depth of the glass. It should be understood that while sometimes described as "holes" or "hole-like,” the defects 172 disclosed herein may generally not be void spaces, but are rather portions of the workpiece which has been modified by laser processing as described herein.
• the defects 172 may generally be spaced apart from one another by a distance of from about 5 microns to about 20 microns.
• suitable spacing between the defects 172 may be from about 0.1 microns to about 30 microns, such as from about 5 microns to about 15 microns, from about 5 microns to about 12 microns, from about 7 microns to about 15 microns, or from about 7 microns to about 12 microns for the TFT/display glass compositions.
• the translation of the transparent workpiece 160 relative to the pulsed laser beam 112 may be performed by moving the transparent workpiece 160 and/or the beam source 110 using one or more translation stages 190.
• the process may also be used to perforate stacks of transparent workpieces 160, such as stacks of sheets of glass, and may fully perforate glass stacks of up to a few mm total height with a single laser pass.
• a single glass stack can comprise of various glass types within the stack, for example one or more layers of soda-lime glass layered with one or more layers of Corning code 2318 glass.
• the glass stacks additionally may have air gaps in various locations.
• ductile layers such as adhesives may be disposed between the glass stacks.
• the pulsed laser process described herein will still, in a single pass, fully perforate both the upper and lower glass layers of such a stack.
• a stress inducing source such as a mechanical or thermal source may be utilized to separate the transparent workpiece 160 along the contour line 170.
• the thermal source such as an infrared laser beam
• an infrared laser may be used to initiate spontaneous separation and then the separation may be finished mechanically.
• Suitable infrared lasers to create thermal stress in glass would typically have wavelengths that are readily absorbed by glass, typically having wavelengths ranging from 1.2 microns to 13 microns, for example, a range of 4 microns to 12 microns.
• the infrared laser beam such as a laser beam produced by a carbon dioxide laser (a "CO 2 laser"), a carbon monoxide laser (a "CO laser”), a solid state laser, a laser diode, or combinations thereof, is a controlled heat source that rapidly increases the temperature of the transparent workpiece 160 at or near the contour line 170. This rapid heating may build compressive stress in the transparent workpiece 160 on or adjacent to the contour line 170. Since the area of the heated glass surface is relatively small compared to the overall surface area of the transparent workpiece 160, the heated area cools relatively rapidly.
• the resultant temperature gradient induces tensile stress in the transparent workpiece 160 sufficient to propagate a crack along the contour line 170 and through the thickness of the transparent workpiece 160, resulting in full separation of the transparent workpiece 160 along the contour line 170.
• the tensile stress may be caused by expansion of the glass (i.e., changed density) in portions of the workpiece with higher local temperature.
• a contour line comprising defects along a desired line of separation may be enhanced by utilizing a pulsed laser beam which is shaped by an optical assembly such that the pulsed laser beam projects a non-axisymmetric beam spot onto the workpiece along the desired line of separation.
• Example 1 is a modeled result of a pulsed laser beam having a 532 nm wavelength output into an example optical assembly having an aspheric optical element that is aligned with the beam pathway (e.g., no offset).
• the pulsed laser beam is output as a symmetric Gaussian beam and is formed into a quasi-non-diffracting beam by the aspheric optical element.
• FIG. 8A depicts an example cross-sectional intensity plot of the pulsed laser beam focal line (e.g., quasi-non diffracting pulsed laser beam focal line). As shown in FIG. 8A, without an offset, the beam spot is radially symmetric.
• FIG. 8A is 3.8 microns.
• FIG. 8B depicts a logarithmic intensity plot of the Fourier transform plane of the quasi-non diffracting pulsed laser beam focal line formed without an offset.
• FIG. 8C depicts an experimental near-field micrograph of the quasi-non diffracting pulsed laser beam focal line formed without an offset at a peak line-focus position.
• Example 2 is a modeled result of a pulsed laser beam having a 1064 nm wavelength output into an example optical assembly having an aspheric optical element that is offset relative to the beam pathway by an offset distance of 20 microns in the X-direction.
• the pulsed laser beam is output as an axisymmetric Gaussian beam and is formed into a quasi- non-diffracting beam by the aspheric optical element.
• FIG. 9 depicts an example cross- sectional intensity plot of the resultant non-axisymmetric pulsed laser beam focal line formed by the offset between the aspheric optical element and the beam pathway.
• Example 3 is a modeled result of a pulsed laser beam having a 1064 nm wavelength output into an example optical assembly having an aspheric optical element that is offset relative to the beam pathway by an offset distance of 50 microns in the X-direction.
• the pulsed laser beam is output as an axisymmetric Gaussian beam and is formed into a quasi- non-diffracting beam by the aspheric optical element.
• FIG. 10 depicts an example cross- sectional intensity plot of the resultant non-axisymmetric pulsed laser beam focal line formed by the offset between the aspheric optical element and the beam pathway.
• Example 4 includes modeled and experimental results of a pulsed laser beam having a 1064 nm wavelength that is output into an example optical assembly having an aspheric optical element that is offset relative to the beam pathway by an offset distance of 100 microns in the X-direction.
• the pulsed laser beam is output as an axisymmetric Gaussian beam and is formed into a quasi-non-diffracting beam by the aspheric optical element.
• FIG. 11A depicts an example cross-sectional intensity plot of the modeled resultant non-axisymmetric pulsed laser beam focal line formed by the offset between the aspheric optical element and the beam pathway.
• FIG. 11B depicts X and Y cross-sections of the cross-sectional intensity plot of the modeled result of FIG.
• FIG. 11A depicts a best focus axial position, which a location approximately mid-way along the length of the pulsed laser beam focal line.
• FIG. l lC depicts a cross-section of the cross-sectional intensity plot of the modeled result of FIG. 11A at an axial position shifted by about 200 microns from the best focus axial position of FIG. 11B.
• the FWHM of the intensity plot of FIG. 11C is 7.0x4.5 microns, showing an asymmetry of about 1.6.
• FIG. 11D depicts a modeled logarithmic intensity plot of the Fourier transform plane of the pulsed laser beam (e.g., quasi-non diffracting pulsed laser beam) formed with a 100 micron offset. As shown in FIG. 11D, the logarithmic intensity plot is not uniform.
• FIG. HE depicts an experimental near-field micrograph of the pulsed laser beam focal line of example 4 at the peak line-focus position.
• a Gauss-Bessel beam convolved with a delta function mathematically describes a Gauss-Bessel at an origin point.
• FIG. 12A depicts a cross sectional intensity plot (along the X-Y plane) of a Bessel-Gauss beam convolved with a delta function.
• FIG. 12B depicts a cross sectional intensity plot (along the X-Y plane) of a Gauss-Bessel beam convolved wit
• equation 33 mathematically describes a convolution
• FIG. 12C depicts a cross sectional intensity plot (along the X-Y plane) of a Gauss-Bessel beam convolved with the Fourier transform of a Heaviside step function as mathematically described in Eq. 33.
• the cross-sectional intensity plot (along the X-Y plane) of FIG. 12C is also the resultant cross sectional intensity of the pulsed laser beam focal line formed by blocking 50% of the beam pathway.
• FIG. 12D graphically depicts X-axis cross sections of the intensity plots of FIGS. 12A-12C and FIG. 12E graphically depicts the Fourier transform of an example Sgn step function.
• FIG. 12F depicts a cross-sectional intensity plot of a resultant non-axisymmetric pulsed laser beam focal line formed when the pulsed laser beam traverses the axicon and 50% of the beam intensity of the pulsed laser beam is blocked by an optical blocking element positioned along the beam pathway halfway between the first lens and the second lens.
• FIG. 12G graphically depicts X and Y cross-sections of the intensity plot of FIG. 12F.
• FIG. 12G graphically depicts X and Y cross-sections of the intensity plot of FIG. 12F.
• FIG. 12H depicts a cross- sectional intensity of a resultant non-axisymmetric pulsed laser beam focal line when 50% of the beam intensity is blocked by an optical blocking element positioned at the beam source (e.g
• FIG. 121 graphically depicts X and Y cross-sections of the intensity plot of FIG. 12H.
• the Z-axis position of the optical blocking element along the beam pathway has minimal effect on the resultant pulsed laser beam focal line.
• the optical blocking element can be effective whether it is placed in the space before the axicon, or after the axicon, such as in the collimation space 134 between the two lens 130 and 132.
• Example 6 is a modeled result of incrementally blocking cross sectional segments of a pulsed laser beam having a 600 micron 1/e diameter.
• example 6 includes blocking different cross section segments of the pulsed laser beam each having an increased maximum blocked width, where the term "maximum blocked width" is defined as the width of the blocked portion of the pulsed laser beam (e.g., the blocked portion of the beam pathway) measured perpendicular from a center point of the cross sectional chord portion of the blocked cross sectional segment.
• FIG. 13 A depicts an example intensity plot in the X-Y plane of the resultant pulsed laser beam focal line without blocking the pulsed laser beam. As shown in FIG. 13 A, with no blocking, the cross-sectional pulsed laser beam focal line is axisymmetric.
• FIGS. 13B-13K depict example intensity plots in the X-Y plane having blocked cross sectional segments with increasing maximum blocked widths.
• the maximum blocked width in FIG. 13B is 50 microns
• the maximum blocked width in FIG. 13C is 100 microns
• the maximum blocked width in FIG. 13D is 150 microns
• the maximum blocked width in FIG. 13E is 200 microns
• the maximum blocked width in FIG. 13F is 250 microns
• the maximum blocked width in FIG. 13G is 300 microns (e.g., blocking half of the pulsed laser beam)
• the maximum blocked width in FIG. 13H is 350 microns
• the maximum blocked width in FIG. 131 is 400 microns
• the maximum blocked width in FIG. 13J is 450 microns
• the maximum blocked width in FIG. 13K is 500 microns.
• a quasi-non-diffracting pulsed laser beam having a wavelength of 532 nm is output into an example optical assembly having an optical blocking element positioned such that the optical blocking element blocks 50% of the pulsed laser beam.
• FIG. 14 depicts a near field micrograph of a cross-section of a non-axisymmetric pulsed laser beam focal line formed by blocking 50% of the pulsed laser beam in example 7.
• a quasi-non-diffracting pulsed laser beam having a wavelength of 532 nm is output into an example optical assembly having an optical blocking element positioned such that the optical blocking element blocks 75% of the pulsed laser beam.
• FIG. 15 depicts a near field micrograph of a cross-section of a non-axisymmetric pulsed laser beam focal line formed by blocking 75% of the pulsed laser beam in example 8. Note that the non-axisymmetric pulsed laser beam focal line of example 8 comprises a larger aspect ratio than the non-axisymmetric pulsed laser beam focal line of example 7.
• an optical blocking element is positioned in an example optical assembly such that the optical blocking element blocks a quarter sector of the cross sectional pulsed laser beam (and thus blocks 25% of the intensity of the pulsed laser beam).
• FIG. 16 depicts example resultant cross-section of non-axisymmetric pulsed laser beam focal lines formed by the optical blocking element at incremental 45° rotations of the optical blocking element about the optical axis (e.g., about the propagation direction of the pulsed laser beam).
• Example 10 models blocking two cross sectional segments of a pulsed laser beam having a 600 micron 1/e diameter at the common focal plane between the first lens and the second lens using two optical blocking elements oriented such that they block cross sectional chord portion of the pulsed laser beam each terminating at parallel chords and each having equal maximum blocked widths (as defined above with respect to example 6).
• FIG. 17A depicts an example intensity plot in the X-Y plane of the resultant pulsed laser beam focal line without blocking the pulsed laser beam. As shown in FIG. 17A, with no blocking, the cross-section of the pulsed laser beam focal line is axisymmetric.
• FIGS. 17B-17F depict example intensity plots in the X-Y plane having two parallel blocked cross sectional segments with increasing and equal maximum blocked widths.
• each maximum blocked width in FIG. 17B is 50 microns
• each maximum blocked width in FIG. 17C is 100 microns
• each maximum blocked width in FIG. 17D is 150 microns
• each maximum blocked width in FIG. 17E is 200 microns
• each maximum blocked width in FIG. 17F is 250 microns.
• the pulsed laser beam focal line cross sections in FIGs. 17A-17F show multiple fringes and much of the laser energy is thrown outside of the central core spot of the pulsed laser beam focal line, even for Figure 17B. This means the central spot has lower intensity and more laser power may be needed at the input of the optical system to facilitate cutting the transparent workpiece.
• the large amount of energy present in the non-central fringes of Figure 17B-17F will also create different stress profiles at the transparent workpiece that do not concentrate the stress as well as when the optical energy is mostly contained in the central ellipse.
• Example 11 is an experimental confirmation of the modeled results of example 10 and is done with an example optical assembly that includes a 632 nm HeNe laser.
• example 11 two optical blocking elements are positioned in the example optical assembly such that each optical blocking element blocks a cross sectional segment of the pulsed laser beam within the collimation space 134 between the two lenses 130 and 132, where the diameter of the collimated beam ring is about 22mm and the cross sectional chord portions formed by each optical blocking element terminate at chords that are positioned parallel and are spaced apart by about 9 mm.
• an optical blocking element is positioned in an example optical assembly that also includes an aspheric optical element which is offset relative to the optical pathway of the pulsed laser beam.
• FIG. 19A depicts a cross sectional image of a pulsed laser beam after the pulsed laser beam traversed an axicon offset from the beam pathway by 50 microns and a half aperture optical blocking element positioned to block 50% of a pulsed laser beam in a non-offset system.
• FIG. 19B depicts an example cross-sectional intensity plot of the resultant non-axisymmetric pulsed laser beam focal line formed by the block and shift arrangement depicted in FIG. 19 A.
• an optical delay plate that induces an optical delay of ⁇ is positioned within a beam pathway such that 50% of the pulsed laser beam traverses the optical delay plate and undergoes an optical delay of ⁇ .
• FIG. 20A depicts a cross-sectional intensity plot of the resultant non-axisymmetric pulsed laser beam focal line formed by the optical delay of ⁇ of 50% of the pulsed laser beam.
• FIG. 20B depicts cross-sections of the cross-sectional intensity plot of FIG. 20A.
• an optical delay plate that induces an optical delay of 0.875 ⁇ is positioned within a beam pathway such that 50% of the pulsed laser beam traverses the optical delay plate and undergoes an optical delay of ⁇ .
• FIG. 21A depicts a cross-sectional intensity plot of the resultant non-axisymmetric pulsed laser beam focal line formed by the optical delay of 0.875 ⁇ of 50% of the pulsed laser beam.
• FIG. 21B depicts a cross-sections of the cross-sectional intensity plot of FIG. 21A.
• an optical delay plate that induces an optical delay of 0.5 ⁇ is positioned within a beam pathway such that 50% of the pulsed laser beam traverses the optical delay plate and undergoes an optical delay of ⁇ .
• FIG. 22A depicts a cross-sectional intensity plot of the resultant non-axisymmetric pulsed laser beam focal line formed by the optical delay of 0.5 ⁇ of 50% of the pulsed laser beam.
• FIG. 22B depicts cross-sections of the cross-sectional intensity plot of FIG. 22A.
• a split quarter waveplate as described above may be positioned in a beam pathway of a laser beam output by a HeNe laser such that a first beam portion of the HeNe laser beam is polarized into a first polarization and a second beam portion of the HeNe laser beam is polarized into a second polarization that is orthogonal the first polarization.
• FIG. 23 depicts example resultant non-axisymmetric pulsed laser beam focal lines formed by the split quarter waveplate at incremental 45° rotations of the example split quarter waveplate about the optical axis (e.g., about the propagation direction of the pulsed laser beam).
• This example describes an optical system for creating an asymmetric quasi non- diffracting beam using a polarization method. An outline of this example follows:
• the optical system shown in Fig. 25 generally outlines a system that can be used to create an asymmetric quasi non-diffracting beam using a polarization method to break the beam asymmetry. This optical system is suitable for cutting substrates such as glasses.
• a representative laser is a 1064nm pulsed laser with a 9 psec pulse width that provides a Gaussian-shaped output beam with linear polarization (e.g. Coherent Hyper-Rapid 50).
• a telescope is used to collimate the beam to a 5.5mm 1/e diameter before it enters the axicon. The beam passes through a quarter wave plate to circularly polarize it before it is incident on the axicon.
• the overall optical system extending from the quarter waveplate (QWP) through the axicon, split quarter wave plate (SQWP), and lenses is designed to convert an input Gaussian beam into an asymmetric quasi non- diffracting beam (QNDB).
• the axicon and lenses will form what is sometimes known as a Gauss-Bessel beam, which is a QNDB with an axisymmetric intensity distribution.
• the quarter waveplate in conjunction with the SQWP serve to break the rotational symmetry of the system, and they are the elements that allow create of an asymmetric QNDB.
• This system is shown in Fig. 26.
• This exact selection of lenses is not critical. Many different focal lengths and style of lenses are possible.
• the point of the collimating lens(es) is that they combine with the objective lens to act as a telescope that optically relays (diameter, length) the focal line formed just after the axicon to create a magnified (or demagnified) image of the focal line after the final focusing lens.
• This allows one to more flexibly scale the size of the focal line without needing to change axicons, and also projects the focal line to a location that has a relatively large physical separation or working distance from the final optic, which is much more convenient in a production environment than have a focal line that is immediately adjacent to an axicon.
• the setups shown in this example are chosen to allow for a long effective focal length of the collimating lenses, while keeping the overall package size relatively short. That is why the two collimating lens approach, where the first lens acts as a "field lens", configuration was used. This specific collimating lens choice is not required in order to make a QNDB or an asymmetric QNDB. Single collimating lenses may also be used, or lenses of other focal lengths.
• the beam is approximately collimated into an annulus as it enters the SQWP, which acts to break the symmetry of the beam through polarization change as described herein.
• the SQWP can rotate about the optical axis of the system in order to change the preferred azimuthal orientation of the asymmetric focused spot.
• the long axis of the asymmetric spot formed will be perpendicular to the divide line in the SQWP.
• the rotation of the SQWP can be motorized and the angle of the orientation can be synchronized to follow the desired cutting path direction in the substrate.
• the SQWP used in this embodiment is important in creating an asymmetric QNDB.
• the SQWP creates a polarization based decoherence of two sections of the laser beam.
• the SQWP is illustrated further is in Figure 7B, but more explicitly in Figure 23.
• a SQWP consist of two section of quarter waveplate, which are assembled so that the optical axes in each section are orthogonal to the optical axes in the other section of the SQWP.
• each portion of the SQWP converts the light passing through each portion into a polarization which is always orthogonal to the polarization from the other portion.
• the light emitted by the first portion may be linear vertical, and the light emitted by the second portion may be linear horizontal.
• the light emitted by the first portion may be right-handed circular, with the light emitted by the second portion being left-handed circular.
• Figure 27 shows a SQWP and a method for constructing a SQWP.
• the two sections are assembled so that the left hand (hashed) half has a fast optical axis that is perpendicular to the fast optical axis of the right half (clear section in this image).
• the SQWP need not be two equal halves. But the orthogonality of the optical axes of the two sections is important.
• Figure 28 shows schematically production of an asymmetric QNDB using the polarization method to decohere the beam.
• the basic mechanism is:
• a collimating lens creates a ring or annular of light
• a focusing lens refocuses the light to form a focal line or QNDB.
• the QNDB will be asymmetric (or elliptical) because the SQWP creates two orthogonally polarized portions of the beam, which can no longer combine coherently.
• NA numerical aperture
• FIG. 29 shows example images of nano-perforations and crack control made with the optical system of Fig. 26. Nano-perfroated holes in non-ion exchanged Corning Code 2318 glass made using the SQWP optical system are shown. A "cross" of holes is made in each image, showing stage/laser beam traversing the vertical (y) direction and in the horizontal (x) direction.
• each image a biased crack direction can be seen that is independent of the x or y direction of motion of the stage - this crack direction is highlighted by the red arrows.
• the split of the SQWP starts oriented parallel to the horizontal (x) direction to make the nano-perforations with nearly vertical (y) cracks shown in the upper left image, and then is the SQWP is rotated in subsequent images by 45 degree steps each time.
• the arrows indicate the observed direction of the biased cracks in each image.
• Figure 30 shows a star pattern with nano-perforation lines at made at four different SQWP rotation angles (Odeg, 45deg, 90deg, 135deg). To make each line, the SQWP was set at a different rotation angle, such that the biased crack direction was controlled to be parallel to the stage motion direction. It is noticeable that crack propagation between the individual nano-perforations exactly follows the intended direction.
• the microscope objective served to magnify and image a cross section of the focal line onto the CCD camera.
• This magnification is such that each camera pixel corresponds to a size of only ⁇ 0.027 microns at a given cross sectional plane of the focal line, allowing even a micron scale beam cross section to be sub-resolved with high fidelity.
• the microscope objective and CCD camera are then scanned along the optical axis of the beam to capture cross sectional profiles of the beam as a function of z.
• Figure 32 is an image obtained with the CCD camera of the beam cross section for one given z-location (location along the optical axis).
• the grayscale shading indicates the intensity of the light, with darker shading being the most intense and lighter shading being the least intense.
• the units of the x/y scales are microns.
• Figure 32 shows an asymmetric beam, with the spot elongated along the horizontal (x) direction.
• Figure 33 is a plot of the peak intensity in cross sectional images obtained at a series of z- locations (locations along the optical axis).
• the intensity units are in analog-to-digital converter bits as measured on each pixel of the camera, and the images are acquired with an 8-bit CCD camera, so the maximum pixel intensity is 255.
• the xy cross-section image shown in Figure 32 was obtained at the position of maximum intensity.
• the optic system shown in Figure 31 was used to create an asymmetric QNDB and the above described CCD camera system was used to characterize the resulting optical beam.
• This example is based on the beam profile measurements shown in Figures 32 and 33.
• the Rayleigh range is the shortest distance over which the beam decays from a peak value to 1 ⁇ 2 of its peak value in the z-direction.
• Figures 34 and 35 show enlargements of the central portion of xy cross section shown in Figure 32 over dimensions 10 microns x 10 microns and 5 microns x 5 microns, respectively.
• Figure 36 shows two traces corresponding to one-dimensional slices in the x-direction (trace with wider central feature) and y-direction (trace with narrower central feature) obtained from the xy cross section shown in Figure 34.
• the cross sectional plots analyzed are those at z ⁇ 1.6mm, the where the intensity along the optical axis was at its peak.
• the x-direction trace (Slice X) is a horizontal cross section of the pixel intensity drawn though the peak intensity pixel of the xy cross section.
• the y-direction trace (Slice Y) is a vertical cross section of the pixel intensity drawn though the peak intensity pixel of the xy cross section.
• Diameter in x direction 1.90 microns (1/e intensity points)
• Example 2 the SQWP shown in the optical system of Figure 31 was rotated by 45 deg relative to the position of the SQWP used in Example 1.
• the optical systems of Example 1 and Example 2 were otherwise identical.
• Figure 37 shows an xy beam cross section and Figure 38 shows peak intensity at different focus positions along the z-direction (direction along the optical axis).
• the data shown in Figures 37 and 38 was obtained in the same way as the data shown in Figures 32 and 33.
• Figures 39 and 40 show enlargements of the central portion of the xy cross section shown in Figure 37 over dimensions 10 microns x 10 microns and 5 microns x 5 microns, respectively.
• ⁇ 1.064 microns
• the Rayleigh range is the shortest distance over which the beam decays from a peak value to 1 ⁇ 2 of its peak value.
• Figure 41 shows two traces corresponding to one-dimensional slices in the -45deg direction (trace with wider central feature) and +45deg direction (trace with narrower central feature) obtained from the xy cross section shown in Figure 37.
• the cross sectional plots analyzed are those at z ⁇ 1.8mm, the where the intensity along the optical axis was at its peak.
• the -45deg trace (Slice -45deg) is a -45 deg cross section (lower left to upper right traversal in the xy cross section of Figure 37) of the pixel intensity drawn though the peak intensity pixel of the xy cross section.
• the +45deg trace (Slice +45deg) is a +45 deg cross section (upper left to lower right traversal in the xy cross section of Figure 37) of the pixel intensity drawn though the peak intensity pixel of the xy cross section.
• Figures 42-45 show how a direct calculation of the optical variance ( ⁇ 2 x (z) or ⁇ 2 y (z)) on a series of beam profiles at different z locations also allow one to calculate the Rayleigh range Z RXimin of a QNDB.
• Figure 42 shows an axisymmetric QNDB profile.
• Figure 43 shows the resulting intensity on the optical axis as a function of z (upper plot), as well as the (square root of) calculated beam variance as a function of z (lower plot).
• the variance in the x-direction and the variance in the y-direction are equal since the beam is rotationally symmetric.
• the x or y Rayleigh ranges are determined by the distances along the z-axis where the ⁇ ⁇ ( ⁇ ) or o y (z) increases by a factor of sqrt(2) above its minimum value. This is equivalent to measuring when ⁇ 2 x (z) or ⁇ 2 y (z) increases by a factor of 2.
• Figures 44 and 45 show the same information for an asymmetric QNDB. This is the same beam shape as generated experimentally in one of the above examples. As the beam is asymmetric, the beam variance in the x direction and y-direction are no longer equal. The variance in the y-direction increases far more quickly with z than the variance in the x- direction, since the beam is narrower in the x-axis and hence diffracts more rapidly in the x- axis. What should be noted here if that the exact same z-locations where the o y (z) rises to a value of 1.4 (i.e. sqrt(2)) relative to its minimum value are the points where the optical intensity I(z) drops to 1 ⁇ 2 of its peak.
• Ranges can be expressed herein as from “about” one particular value, and/or to "about” another particular value. When such a range is expressed, another embodiment includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent "about,” it will be understood that the particular value forms another embodiment. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint.

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