Transparent material processing with an ultrashort pulse laser

Abstract

Methods, devices, and systems for ultrashort pulse laser processing of optically transparent materials are disclosed, with example applications in scribing, marking, welding, and joining. For example, ultrashort laser pulses create scribe features with one pass of the laser beam across the material, with at least one of the scribe features being formed below the surface of the material. Slightly modifying the ultrashort pulse laser processing conditions produces sub-surface marks. When properly arranged, these marks are clearly visible with correctly aligned illumination. Reflective marks may also be formed with control of laser parameters. A transparent material other than glass may be utilized. A method for welding transparent materials uses ultrashort laser pulses to create a bond through localized heating. In some embodiments of transparent material processing, a multifocus beam generator simultaneously forms multiple beam waists spaced depthwise relative to the transparent material, thereby increasing processing speed.

What is claimed is: 
     
         1 . A laser-based system for modification of a transparent material, comprising:
 a pulsed laser apparatus generating a pulsed laser output comprising at least one pulse having a pulse width in the range from about 10 fs to 100 ps;   a multifocus beam generator receiving said output, said generator configured to form a plurality of focused beams using said pulsed laser output, each focused beam having a beam waist, said beam waists spaced depthwise relative to said material, at least one beam waist of said plurality of focused beams being within said material and causing modification of said material, said plurality of focused beams comprising different polarizations or different wavelengths generated in different optical paths;   a motion system to produce relative movement between said material and said focused beams; and   a controller coupled to said pulsed laser apparatus and to said motion system, and controlling said system in such a way that said plurality of focused beams are formed during said relative motion, wherein said controller is coupled to said multifocus beam generator, said controller and said multifocus beam generator being configured to control at least one of polarization, wavelength, fluence, and beam waist position of said focused beams,   wherein depthwise separated focused pulsed beams having said different polarizations or different wavelengths are simultaneously delivered to said material during said motion,   wherein said multifocus beam generator comprises beam splitters and beam combiners configured to propagate beams along multiple optical paths, and focusing elements configured to control focus of said beams and to form said depthwise spaced beam waists   
     
     
         2 . The laser-based system of  claim 1 , wherein said multifocus beam generator comprises a wavelength converter, and said focused beams comprise multiple wavelengths. 
     
     
         3 . The laser-based system of  claim 2 , wherein a first wavelength is an IR wavelength and a second wavelength is a visible or near UV wavelength longer than an absorption edge of said material. 
     
     
         4 . The laser-based system of  claim 1 , wherein said multifocus beam generator comprises polarizing elements, and said focused beams comprise multiple polarizations. 
     
     
         5 . The laser-based system of  claim 4 , wherein said polarizations comprise a circular polarization. 
     
     
         6 . The laser-based system of  claim 1 , wherein said pulsed laser apparatus generates laser output pulses at a repetition rate in the range of about 10 kHz to 100 MHz, and said multifocus beam generator is configured to form said plurality of focused beams at said repetition rate. 
     
     
         7 . The laser based system of  claim 1 , wherein said multifocus beam generator comprises a wavelength converter and polarizing elements, and is configured to form focused beams comprising both multiple wavelengths and multiple polarizations focused at different position or depths. 
     
     
         8 . The laser-based system of  claim 1 , wherein said system is operably arranged to generate sub-surface marks in a transparent material. 
     
     
         9 . The laser-based system of  claim 8 , wherein said sub-surface marks comprise reflective marks. 
     
     
         10 . The laser-based system of  claim 1 , wherein said system is operably arranged to weld, join, or bond transparent materials. 
     
     
         11 . The laser-based system of  claim 1 , wherein said system is operably arranged for laser scribing. 
     
     
         12 . The laser-based system of  claim 11 , wherein scribe features are created simultaneously and are located both on the surface and in the bulk of the material. 
     
     
         13 . The laser-based system of  claim 1 , wherein said laser-based system is operably arranged such that a plurality of focused beams form a plurality of features on or within said material, each said feature characterized by having a controlled longitudinal span ranging from a dot shaped feature associated with tight focusing to elongated features having a large aspect ratio of depth to width. 
     
     
         14 . A laser-based method for modification of a material, comprising:
 generating a pulsed laser input beam, said pulsed laser input beam comprising a pulse width less than 100 ps;   forming a plurality of focused pulsed beams with different polarizations or different wavelengths from said pulsed laser input beam, wherein said forming comprises:   spatially separating said pulsed laser input beam to form at least two pulsed beams propagating in at least two respective beam paths; and   combining said at least two beams to form a plurality of collinear beams along a common propagation path, and focusing said at least two pulsed beams;   each focused pulsed beam having a beam waist, respective beam waists of said focused pulsed beams being separated and spaced depthwise along said common propagation path relative to said material, at least one of said beams waists of said focused pulsed beams being within said material and causing material modification within said material that generates at least one sub-surface feature;   producing relative motion between said material and said focused pulsed beams; and   controlling said forming and said moving in such a way that said plurality of collinear, depthwise separated focused pulsed beams having said different polarizations or wavelengths are simultaneously delivered to said material during said motion, with control of at least one of polarization, wavelength, fluence, and beam waist position of said focused pulsed beams.   
     
     
         15 . The method of  claim 14 , wherein said material comprises a tempered glass. 
     
     
         16 . The method of  claim 14 , wherein said material comprises sapphire, or a semiconductor, and said focused pulsed beams comprise a wavelength at which said material is highly transmissive. 
     
     
         17 . The method of  claim 14 , wherein said features are formed that modify both a surface portion and a sub-surface portion of the material. 
     
     
         18 . The method of  claim 14 , wherein at least one focused beam creates a fluence in the range of about 1 J/cm 2  to 150 J/cm 2  within the material. 
     
     
         19 . The laser-based method of  claim 14 , wherein said material modification comprises sub-surface marks formed in a transparent material. 
     
     
         20 . The laser-based method of  claim 19 , wherein said sub-surface marks comprise reflective marks. 
     
     
         21 . The laser-based method of  claim 14 , wherein said method welds, joins, or bonds transparent materials. 
     
     
         22 . The laser-based method of  claim 14 , wherein said method scribes a transparent material. 
     
     
         23 . The laser-based method of  claim 14 , wherein said modification of material comprises scribe features created simultaneously, said scribe features being located both on the surface and in the bulk of the material. 
     
     
         24 . A laser-based system for modification of a transparent material, comprising:
 a pulsed laser apparatus generating a pulsed laser output comprising at least one pulse having a pulse width in the range from about 10 fs to 100 ps;   a multifocus beam generator receiving said output, said generator configured to form a plurality of focused beams using said pulsed laser output, each focused beam having a beam waist, said beam waists spaced depthwise relative to said material, at least one beam waist of said plurality of focused beams being within said material and causing modification of said material, said plurality of focused beams comprising different polarizations or different wavelengths generated in different optical paths, wherein said multifocus beam generator comprises a wavelength converter and polarizing elements, and is configured to form focused beams comprising both multiple wavelengths and multiple polarizations focused at different positions or depths;   a motion system to produce relative movement between said material and said focused beams; and   a controller coupled to said pulsed laser apparatus and to said motion system, and controlling said system in such a way that said plurality of focused beams are formed during said relative motion,   wherein depthwise separated focused pulsed beams having said different polarizations and different wavelengths are simultaneously delivered to said material during said motion.   
     
     
         25 . The laser-based system of  claim 24 , wherein said multifocus beam generator comprises beam splitters and beam combiners, and focusing elements configured to control focus of said beams and to form said depthwise spaced beam waists. 
     
     
         26 . A laser-based method for generating patterns of features below a surface of a transparent material, comprising:
 forming a plurality of lines at different depths within the material using tightly focused ultrashort laser pulses;   controlling laser parameters such that at least one line comprises an extended planar region having a strong specular reflection component, and wherein said plurality of lines comprise reflective marks formed in such a way that visibility is maximized with a viewing angle approximately equal to an illumination angle, corresponding to viewing at or near a specular angle.   
     
     
         27 . The method of  claim 26 , wherein said laser parameters comprise a pulse width, and said pulse width is in the range of about 300 fs to 25 ps. 
     
     
         28 . The method of  claim 26 , wherein said transparent material comprises microscope slide glass or chemical-resistant borosilicate glass. 
     
     
         29 . The method of  claim 26 , wherein a numerical aperture of a beam of said tightly focused ultrashort pulses is in the range from about 0.3 to 0.55. 
     
     
         30 . The method of  claim 26 , wherein said reflective marks are formed with average laser power up to 1 Watt (W). 
     
     
         31 . A device for generating a detectable spatial pattern in response to controlled irradiation comprising:
 a substantially transparent medium having at least one feature formed therein, said at least one feature having a depth, width, and a physical property for producing detectable radiation along a detection direction in response to controlled irradiation incident along a irradiation direction, said detectable radiation being representative of said spatial pattern, and wherein at least said optical property substantially limits detection along said detection direction in response to unwanted radiation.   
     
     
         32 . A system having the device according to  claim 31 , and further comprising:
 an illuminator for selectively irradiating said device so as to form at least one detectable spatial pattern.   
     
     
         33 . An article made according to the method of  claim 14 , said method comprising: separating material to obtain a portion of said article.