Patent ID: 8173930

Claim:
An apparatus for cutting a substrate, comprising: a plurality of laser oscillators generating at least first and second femtosecond laser beams; a plurality of condenser lenses receiving the at least first and second femtosecond laser beams, and condensing the received at least first and second femtosecond laser beams to have first and second focal depths being different from each other, respectively; a reflector reflecting the first condensed femtosecond laser beam; an optical attenuator between the reflector and the first condenser lens to adjust energy of the femtosecond laser beams; and a beam splitter receiving and splitting the condensed at least first and second femtosecond laser beams, and irradiating the split at least first and second femtosecond laser beams at different depths in the direction vertical to the substrate to be cut, wherein the optical attenuator includes a λ/2 plate, a linear polarizer, and a λ/4 plate are the three parts.