Transparent material cutting with ultrafast laser and beam optics

Abstract

A system for laser drilling of a material includes a pulsed laser configured to produce a pulsed laser beam having a wavelength less than or equal to about 850 nm, the wavelength selected such that the material is substantially transparent at this wavelength. The system further includes an optical assembly positioned in the beam path of the laser, configured to transform the laser beam into a laser beam focal line oriented along the beam propagation direction, on a beam emergence side of the optical assembly.

What is claimed is: 
     
         1 . A system for laser drilling of a material, the system comprising:
 a pulsed laser configured to produce a pulsed laser beam having a wavelength less than or equal to about 850 nm; and   an optical assembly positioned in the beam path of the laser, configured to transform the laser beam into a laser beam focal line oriented along a beam propagation direction, on the beam emergence side of the optical assembly, the optical assembly including a focusing optical element with spherical aberration configured to generate the laser beam focal line, said laser beam focal line adapted to generate an induced absorption within the material, the induced absorption producing a defect line having a diameter less than or equal to about 300 nm along the laser beam focal line within the material.   
     
     
         2 . The system of  claim 1 , wherein the laser beam has a wavelength less than or equal to about 775 nm. 
     
     
         3 . The system of  claim 2 , wherein the laser beam has a wavelength less than or equal to about 600 nm. 
     
     
         4 . The system of  claim 3 , wherein the laser beam has a wavelength less than or equal to about 532 nm. 
     
     
         5 . The system of  claim 1 , wherein the induced absorption produces subsurface damage up to a depth less than or equal to about 75 μm within the material. 
     
     
         6 . The system of  claim 1 , wherein the induced absorption produces an Ra surface roughness less than or equal to about 0.5 μm. 
     
     
         7 . The system of  claim 1 , wherein the optical assembly includes an annular aperture positioned in the beam path of the laser before the focusing optical element, the annular aperture configured to block out one or more rays in the center of the laser beam so that only marginal rays outside the center are incident on the focusing optical element, and thereby only a single laser beam focal line, viewed along the beam direction, is produced for each pulse of the pulsed laser beam. 
     
     
         8 . The system of  claim 1 , wherein the focusing optical element is a spherically cut convex lens. 
     
     
         9 . The system of  claim 1 , wherein the focusing optical element is a conical prism having a non-spherical free surface. 
     
     
         10 . The system of  claim 9 , wherein the conical prism is an axicon. 
     
     
         11 . The system of  claim 1 , wherein the optical assembly further includes a defocusing optical element, the optical elements positioned and aligned such that the laser beam focal line is generated on the beam emergence side of the defocusing optical element at a distance from the defocusing optical element. 
     
     
         12 . The system of  claim 1 , wherein the optical assembly further includes a second focusing optical element, the two focusing optical elements positioned and aligned such that the laser beam focal line is generated on the beam emergence side of the second focusing optical element at a distance from the second focusing optical element. 
     
     
         13 . The system of  claim 1 , wherein the pulsed laser is configured to emit pulses produced in bursts of at least two pulses separated by a duration in a range of between about 1 nsec and about 50 nsec, and the burst repetition frequency is in a range of between about 1 kHz and about 2 MHz. 
     
     
         14 . The system of  claim 13 , wherein the pulses are separated by a duration of about 20 nsec. 
     
     
         15 . The system of  claim 1 , wherein the laser beam focal line has a length in a range of between 0.1 mm and 100 mm. 
     
     
         16 . The system of  claim 1 , wherein the laser beam focal line has an average spot diameter in a range of between 0.1 μm and 5 μm.