Method and apparatus for decorrelation of spatially and temporally coherent light

Abstract

A method and apparatus for decorrelating coherent light from a light source, such as a pulsed laser, in both time and space in an effort to provide intense and uniform illumination are provided. The techniques and apparatus described herein may be incorporated into any application where intense, uniform illumination is desired, such as pulsed laser annealing, welding, ablating, and wafer stepper illuminating.

1 . A method for decorrelating a coherent light beam, comprising:
 circularly polarizing the coherent light beam;   transmitting the circularly polarized light beam through a plurality of optically coupled glass plates;   reflecting the transmitted circularly polarized light beam for transmission back through the plurality of glass plates, wherein each of the glass plates reflects a portion of the transmitted circularly polarized light beam and reflects a portion of the reflected circularly polarized light beam such that a plurality of component beams are created, separated in both time and space from each other; and   linearly polarizing the reflected circularly polarized light beam.   
     
     
         2 . The method of  claim 1 , wherein circularly polarizing the coherent light beam comprises receiving the coherent light beam with a polarizing beam splitter coupled to a wave plate and wherein linearly polarizing the reflected circularly polarized light beam comprises receiving the reflected circularly polarized light beam with the wave plate coupled to the polarizing beam splitter. 
     
     
         3 . The method of  claim 1 , wherein the plurality of glass plates are disposed with increased spacing in a transmission direction of the circularly polarized light beam. 
     
     
         4 . A method for decorrelating a coherent light beam, comprising:
 dividing the coherent light beam into a plurality of component beams;   separating the plurality of component beams in both space and time; and   recombining at least a portion of the separated component beams to form an incoherent light beam.   
     
     
         5 . The method of  claim 4 , further comprising circularly polarizing the coherent light beam before dividing the coherent light beam and linearly polarizing the incoherent light beam. 
     
     
         6 . The method of  claim 4 , wherein dividing the coherent light beam comprises directing the coherent light beam through a plurality of optically coupled glass plates, wherein each of the glass plates transmits a portion of incident light and reflects a remaining portion of the incident light. 
     
     
         7 . The method of  claim 6 , wherein the plurality of glass plates is optically coupled to a reflecting device to redirect the plurality of component beams back through the plurality of glass plates. 
     
     
         8 . The method of  claim 6 , wherein separating the plurality of component beams in time comprises disposing the plurality of glass plates such that the spacing between any two adjacent glass plates of the plurality is different than the spacing between any other two adjacent glass plates of the plurality. 
     
     
         9 . The method of  claim 8 , wherein the plurality of glass plates are disposed with increased spacing from a first end of the plurality to a second end of the plurality and the first end of the plurality of glass plates receives the coherent light beam. 
     
     
         10 . An apparatus for decorrelating coherent light, comprising:
 a polarizing beam splitter configured to receive the coherent light;   a wave plate coupled to the polarizing beam splitter;   a plurality of optically coupled glass plates, the plurality having a first end and a second end wherein the first end is optically coupled to the wave plate; and   a reflecting device optically coupled to the second end of the plurality of glass plates.   
     
     
         11 . The apparatus of  claim 10 , wherein the polarizing beam splitter is configured to output incoherent light after light incident on the polarizing beam splitter is transmitted through the wave plate, reflected by and transmitted through each of the plurality of glass plates, reflected by the reflecting device, re-reflected by and retransmitted through each of the plurality of glass plates, and retransmitted through the wave plate. 
     
     
         12 . The apparatus of  claim 10 , wherein the coherent light is s-polarized and the incoherent light is p-polarized. 
     
     
         13 . The apparatus of  claim 10 , wherein the coherent light is linearly polarized and the wave plate is configured to circularly polarize the linearly polarized coherent light as the coherent light is transmitted from the polarizing beam splitter through the wave plate to the plurality of glass plates. 
     
     
         14 . The apparatus of  claim 10 , wherein light transiting the plurality of glass plates is circularly polarized and the wave plate is configured to linearly polarize light received from the plurality of glass plates. 
     
     
         15 . The apparatus of  claim 10 , wherein the plurality of glass plates is disposed with increased spacing from the first end to the second end. 
     
     
         16 . The apparatus of  claim 10 , wherein the reflecting device is a retroreflector. 
     
     
         17 . A laser processing system, comprising:
 a laser source for providing coherent light;   a decorrelator coupled to the laser source, comprising:
 a polarizing beam splitter configured to receive the coherent light; 
 a wave plate coupled to the polarizing beam splitter; 
 a plurality of optically coupled glass plates, the plurality having a first end and a second end wherein the first end is optically coupled to the wave plate; and 
 a reflecting device optically coupled to the second end of the plurality of glass plates; and 
   a target coupled to the decorrelator, wherein the target receives incoherent light.   
     
     
         18 . The system of  claim 17 , wherein the laser processing system is a pulsed laser annealing system. 
     
     
         19 . The system of  claim 17 , wherein the target is a substrate for a semiconductor. 
     
     
         20 . The system of  claim 17 , wherein the polarizing beam splitter is configured to output the incoherent light after light incident on the polarizing beam splitter is transmitted through the wave plate, reflected by and transmitted through each of the plurality of glass plates, reflected by the reflecting device, re-reflected and retransmitted through each of the plurality of glass plates, and retransmitted through the wave plate.