Optical structure for adjusting the peak power of a laser beam

Abstract

Structure is disclosed for the ablation of material by the use of a laser beam wherein the laser provides a beam which is directed through an illumination and projection optical system for imaging on the material which is to be ablated. In the present invention the peak power of the laser beam is adjustable. The laser beam peak power adjustment structure includes a laser that provides a pulsed beam. The laser beam is directed into a beam splitter wherein the laser beam is split into two beam components. The first beam component passes through beam splitter with negligible or no delay, then passes through a quarter waveplate and impinges on a first mirror which reflects it back to the beam splitter. The second beam component is directed at an angle of 90 degrees by the beam splitter and toward a second mirror. The second mirror is at a predetermined distance from the beam splitter which introduces a total predetermined delay for the reflected second beam component as it is directed back to the beam splitter. The reflected first beam component and the delayed reflected second beam component are combined at the beam splitter to form a third beam which passes from the beam splitter toward the conventional optical column for the ablation tool including the mask and target. The resultant third beam directed to the mask therefore consists of original beam pulses and delayed beam pulses which combine to reduce the peak power of the third beam component.

Dependencies are inferred from the claim text.