System and method for eliminating the structure and edge roughness produced during laser ablation of a material

Abstract

The present technology relates generally to laser ablation, and more particularly pertains to a system and method for eliminating structure and edge roughness, which is produced during the laser ablation of a material. Ablation of materials using a femtosecond laser beam produces a fine scale periodic structure in the ablated region. The structure consists of residual (i.e. unablated material) and is always perpendicular to the polarization direction of the laser beam. By changing the polarization direction during the ablation process, the structure is averaged over many directions and thus eliminated. This eliminates structure and edge roughness in a material caused by the laser ablation of the material. The method is employed to the repairing of photomasks so as to cause the optical quality thereof to be improved.

1 . A system of reducing periodic structures formed in a photomask material during a laser ablation process, the method system:
 a laser for producing incident linearly polarized laser light;   means for converting the incident linearly polarized laser light to circularly or eliptically polarized laser light; and   means for averaging a plurality of polarization directions during the laser ablation process.   
   
   
       2 . The system as claimed in  claim 1 , wherein the means for polarizing and averaging comprise a quarter wave plate inserted into an optical path of the linearly polarized laser light to produce said circularly or eliptically polarized light. 
   
   
       3 . The system as claimed in  claim 1 , wherein the means for polarizing comprises a half wave plate inserted into an optical path of the linearly polarized laser light to alter the direction of polarization. 
   
   
       4 . The system as claimed in  claim 1 , wherein the means for averaging comprises means for rotating the half wave plate during the laser ablation process.