Transparent material processing with an ultrashort pulse laser

• US 7,626,138 B2
• Filed: 09/08/2006
• Issued: 12/01/2009
• Est. Priority Date: 09/08/2005
• Status: Active Grant

• Current Assignee: IMRA America Incorporated (Aisin Corp.)
• Original Assignee: IMRA America Incorporated (Aisin Corp.)
• Inventors: Arai, Alan Y., Bovatsek, James, Yoshino, Fumiyo
• Primary Examiner(s): Evans; Geoffrey S
• Application Number:
  US11/517,325
• Publication Number:
  US 20070051706A1
• Time in Patent Office: 1,180 Days
• Field of Search: 219/121.68, 219/121.69, 347/224, 362/553, 362/555, 362/559
• US Class Current: 219/121.69
• CPC Class Codes: B23K 2103/50 Inorganic material, e.g. metals, not provided for in B23K2103/02 – B23K2103/26
• CPC Class Codes: B23K 26/0617 and with spots spaced along the common axis
• CPC Class Codes: B23K 26/0624 using ultrashort pulses, i.e. pulses of 1ns or less
• CPC Class Codes: B23K 26/244 Overlap seam welding
• CPC Class Codes: B23K 26/364 for making a groove or trench, e.g. for scribing a break initiation groove
• CPC Class Codes: B23K 26/40 taking account of the properties of the material involved
• CPC Class Codes: B23K 26/53 for modifying or reforming the material inside the workpiece, e.g. for producing break initiation cracks
• CPC Class Codes: B28D 5/0011 with preliminary treatment, e.g. weakening by scoring
• CPC Class Codes: B29C 59/16 by wave energy or particle radiation , e.g. infrared heating B29C59/007 takes precedence
• CPC Class Codes: B29C 65/00 Joining or sealing of preformed parts , e.g. welding of plastics materials; Apparatus therefor general aspects of processes or apparatus for joining preformed parts B29C66/00; using porous material formed by internal pressure generated therein for joining preformed parts B29C44/1228, B29C44/326
• CPC Class Codes: B29C 65/14 using wave energy , i.e. electromagnetic radiation, or particle radiation using mechanical waves B29C65/06; using ultrasonic waves B29C65/08; pressing means transparent to electromagnetic radiation B29C66/81267
• CPC Class Codes: B29C 65/1616 Near infrared radiation [NIR], e.g. by YAG lasers
• CPC Class Codes: B29C 65/1635 at least passing through one of the parts to be joined, i.e. laser transmission welding
• CPC Class Codes: B29C 65/1638 focusing the laser beam on the interface
• CPC Class Codes: B29C 65/1658 scanning once, e.g. contour laser welding
• CPC Class Codes: B29C 65/1664 making use of several radiators
• CPC Class Codes: B29C 65/1674 making use of laser diodes B29C65/167 takes precedence
• CPC Class Codes: B29C 65/1696 making use of masks
• CPC Class Codes: B29C 65/38 Impulse heating
• CPC Class Codes: B29C 66/1122 Single lap to lap joints, i.e. overlap joints B29C66/45, B29C66/472, B29C66/52272 take precedence
• CPC Class Codes: B29C 66/30223 : said melt initiators being rib-like
• CPC Class Codes: B29C 66/322 : Providing cavities in the joined article to collect the burr
• CPC Class Codes: B29C 66/3282 : for reinforcing the joint
• CPC Class Codes: B29C 66/41 : Joining substantially flat articles B29C66/47 and subgroups take precedence; Making flat seams in tubular or hollow articles B29C66/51 and subgroups take precedence
• CPC Class Codes: B29C 66/43 : Joining a relatively small portion of the surface of said articles B29C66/45 takes precedence
• CPC Class Codes: B29C 66/71 : characterised by the composition of the plastics material of the parts to be joined welding bar compositions B29C65/125
• CPC Class Codes: B29C 66/73366 : both parts to be joined being transparent or translucent to visible light
• CPC Class Codes: B29C 66/7352 : Thickness, e.g. very thin
• CPC Class Codes: B29C 66/73921 : characterised by the materials of both parts being thermoplastics
• CPC Class Codes: B29C 66/836 : Moving relative to and tangentially to the parts to be joined, e.g. transversely to the displacement of the parts to be joined, e.g. using a X-Y table B29C66/65 takes precedence
• CPC Class Codes: B29C 66/91641 : the heat or the thermal flux being non-constant over time
• CPC Class Codes: B29C 66/919 : characterised by specific temperature, heat or thermal flux values or ranges specific electrical resistance values B29C66/81262
• CPC Class Codes: B29C 66/934 : by controlling or regulating the speed
• CPC Class Codes: B29C 66/939 : characterised by specific speed values or ranges
• CPC Class Codes: B29C 66/944 : by controlling or regulating the time
• CPC Class Codes: B29C 66/949 : characterised by specific time values or ranges
• CPC Class Codes: B29K 2033/12 : Polymers of methacrylic acid esters, e.g. PMMA, i.e. polymethylmethacrylate
• CPC Class Codes: B29K 2069/00 : Use of PC, i.e. polycarbonates or derivatives thereof, as moulding material
• CPC Class Codes: B29K 2995/0026 : Transparent
• CPC Class Codes: B81B 1/00 : Devices without movable or flexible elements, e.g. microcapillary devices
• CPC Class Codes: B81C 1/00119 : Arrangement of basic structures like cavities or channels, e.g. suitable for microfluidic systems
• CPC Class Codes: C03B 23/20 : Uniting glass pieces by fusing without substantial reshaping
• CPC Class Codes: C03B 23/203 : Uniting glass sheets C03B23/24 takes precedence
• CPC Class Codes: C03B 33/0222 : Scoring using a focussed radiation beam, e.g. laser
• CPC Class Codes: C03C 23/0025 : by a laser beam
• CPC Class Codes: Y10T 428/13 : Hollow or container type article [e.g., tube, vase, etc.]
• CPC Class Codes: Y10T 428/15 : Sheet, web, or layer weakened to permit separation through thickness
• CPC Class Codes: Y10T 428/24479 : including variation in thickness
• CPC Class Codes: Y10T 428/24802 : Discontinuous or differential coating, impregnation or bond [e.g., artwork, printing, retouched photograph, etc.]

Abstract

Methods for ultrashort pulse laser processing of optically transparent materials. A method for scribing transparent materials uses ultrashort laser pulses to create multiple scribe features with a single pass of the laser beam across the material, with at least one of the scribe features being formed below the surface of the material. This enables clean breaking of transparent materials at a higher speed than conventional techniques. Slightly modifying the ultrashort pulse laser processing conditions produces sub-surface marks. When properly arranged, these marks are clearly visible with side-illumination and not clearly visible without side-illumination. In addition, a method for welding transparent materials uses ultrashort laser pulses to create a bond through localized heating. The ultrashort pulse duration causes nonlinear absorption of the laser radiation, and the high repetition rate of the laser causes pulse-to-pulse accumulation of heat within the materials. The laser is focused near the interface of the materials, generating a high energy fluence at the region to be welded. This minimizes damage to the rest of the material and enables fine weld lines.

Claims

1. A method for generating visible patterns of laser-modified features below the surface of a transparent material, comprising:

forming a plurality of lines at different depths within the material using a tightly focused ultrashort pulse laser outputs, said tightly focused outputs having controllably varied focal points and sufficient fluence so as to create regions of material modification at said different depths below said surface;

controlling the roughness of said lines by controlling parameters of said laser; and

illuminating said lines using light propagating generally perpendicular to said lines, wherein said patterns are clearly visible to the unaided eye when illuminated from the perpendicular and substantially invisible to the unaided eye under ambient light.

2. A method as claimed in claim 1, where the illuminating step is conducted by directing a focused light source upon said lines or by directing the light to said lines via an optical waveguide with an output numerical aperture selected to efficiently illuminate the pattern.

3. A method as claimed in claim 1, wherein different ones of said lines are at defined angles relative to one another, and said illuminating step is performed by directing light to said lines from plural sources, each one of which directs light in a direction generally perpendicular to a subset of said lines.

4. A method of controlling the visibility of ultrashort laser-induced sub-surface markings in a transparent material by controlling the width, length and smoothness of individual lines and the density of the lines that form the markings, wherein said markings are clearly visible to the unaided eye when illuminated from the perpendicular, and substantially invisible to the unaided eye under ambient light.

5. A device comprising a transparent material having patterns of sub-surface markings formed with tightly focused ultrashort pulse laser outputs, said tightly focused outputs having controllably positioned focal points and sufficient fluence so as to create regions of material modification at different depths below a surface of the material, wherein the markings are formed of lines at different depths within the material, said lines being substantially visible to the unaided eye only when illuminated with a light source directed generally perpendicular to the lines.

6. The device of claim 5, wherein said lines are disposed at different depths in such a way that illumination of a feature with directional illumination provides high contrast relative to contrast obtainable with non-directional illumination.

7. The device of claim 5, wherein said lines are illuminated with focused illumination.

8. The device of claim 5, further comprising at least one optical waveguide that receives illumination from said source and delivers illumination to at least a portion of a line.

9. The device of claim 5, wherein said transparent material comprises first and second surfaces that confine illumination from said light source with total internal reflection.

10. The device of claim 5, wherein said device is configured in such a way that illumination received from multiple sources either simultaneously or separately directs light generally perpendicular to a line.

11. A system comprising:

A device as claimed in claim 5;

means, comprising at least one light source, for selectively directing illumination toward at least a portion of one or more lines.

12. The system of claim 11, wherein said means comprises multiple sources, said means being controllable in such a way that illumination directed from the multiple sources either simultaneously or separately directs light generally perpendicular to the lines.

13. A system for generating visible patterns of laser-modified features below the surface of a transparent material, said features comprising a plurality of lines, said system comprising:

an ultrashort pulse laser that generates pulses at a repetition rate in the range from about 100 KHz to about 5 MHz;

an optical system for focusing laser pulses emitted from said laser into tightly focused spots below said surface;

a positioning means for three-dimensional positioning of said substrate relative to said laser pulses;

a controller coupled to said laser, optical system, and said positioning means for controllably delivering said tightly focused spots to form features at different depths below said surface such that said patterns are clearly visible to the unaided eye when illuminated from the perpendicular, and substantially invisible to the unaided eye under ambient light.

14. A method for generating visible patterns of laser-modified features below the surface of a transparent material, comprising:

forming a plurality of lines at different depths within the material using tightly focused ultrashort pulse laser outputs, said tightly focused outputs having controllably varied focal points and sufficient fluence so as to create regions of material modification at said different depths below said surface;

controlling the roughness of said lines by controlling parameters of said laser, wherein said patterns are clearly visible to the unaided eye when illuminated from the perpendicular, and substantially invisible to the unaided eye under ambient light.

15. The method as claimed in claim 14, further comprising:

illuminating said lines using light propagating generally perpendicular to said lines.