Dual-beam laser processing system

Abstract

A system for forming two laser processing beams with controlled stability at a target specimen work surface includes first and second mutually coherent laser beams propagating along separate first and second beam paths that are combined to perform an optical property adjustment. The combined laser beams are separated into third and fourth laser beams propagating along separate beam paths and including respective third and fourth main beam components, and one of the third and fourth laser beams contributes a leakage component that copropagates in mutual temporal coherence with the main beam component of the other of the third and fourth laser beams. An effect of mutual temporal coherence of the leakage component and the other main beam component with which the leakage component copropagates is reduced through acousto-optic modulation frequency shifts or through incorporation of an optical path length difference in the two beams.

1 . A dual-beam laser processing system, comprising:
 a laser source emitting a laser beam;   a first polarizing beam splitter separating the laser beam into first and second mutually coherent laser beams;   first and second optical modulators through which pass the respective first and second mutually coherent laser beams;   an optical path-length adjuster through which one of the first and second mutually coherent laser beams pass, the optical path-length adjuster reducing mutual coherence of the first and second laser beams by introducing an optical path-length difference between the first and second laser beams and thereby forming first and second reduced coherency laser beams;   a second polarizing beam splitter recombining the first and second reduced coherency laser beams and thereby forming a recombined laser beam;   an optical property adjuster through which the recombined laser beam passes; and   a third polarizing beam splitter separating the recombined laser beam into third and fourth laser beams for use in processing a target specimen.   
     
     
         2 . The system of  claim 1 , in which the optical property adjuster comprises a variable beam expander. 
     
     
         3 . The system of  claim 1 , in which the optical path-length adjuster comprises an air path that introduces the optical path-length difference. 
     
     
         4 . The system of  claim 1 , in which the optical path-length adjuster comprises a refractive optical element. 
     
     
         5 . The system of  claim 4 , in which the refractive optical element comprises fused silica glass. 
     
     
         6 . The system of  claim 1 , in which the first and second mutually coherent laser beams have a coherence length, and in which the optical path-length difference is greater than the coherence length. 
     
     
         7 . A dual-beam laser processing system with controlled beam stability at a work surface of a target specimen, comprising:
 a laser source emitting a laser beam;   a first polarizing beam splitter separating the laser beam into first and second laser beams;   first and second acousto-optic modulators through which the respective first and second laser beams pass;   a second polarizing beam splitter recombining the first and second laser beams and thereby forming a recombined laser beam;   an optical property adjuster through which the recombined laser beam passes;   a third polarizing beam splitter separating the recombined laser beam into third and fourth laser beams for use in processing the target specimen, one of the third and fourth laser beams contributing a leakage component that copropagates in mutual temporal coherence with the other of the third and fourth laser beams; and   one of the first and second acousto-optic modulators being adjusted to impart to the first and second laser beams, and thereby to the leakage component, a change in a crosstalk frequency, Δω, such that the change in the crosstalk frequency reduces an effect of the mutual temporal coherence of the leakage component and the other of the third and fourth laser beams with which the leakage component copropogates to deliver to the target specimen stabilized first and second processing beams corresponding to the third and fourth laser beams.   
     
     
         8 . The system of  claim 7 , in which the optical property adjuster comprises a variable beam expander. 
     
     
         9 . The system of  claim 7 , in which the one of the first and second acousto-optic modulators is adjusted to set the crosstalk frequency, Δω, by driving, respectively, the first and second laser beams at different frequencies from each other, respectively ω s1  and ω s2 , where Δω=ω s1 −ω s2 . 
     
     
         10 . The system of  claim 7 , in which the one of the first and second acousto-optic modulators is adjusted to set the crosstalk frequency, Δω, to a diffractive order, n, of the first acousto-optic modulator to a different diffractive order, m, of the second acousto-optic modulator.