Patent ID: 7436423

Claim:
An apparatus for making a grayscale photo mask of a glass material that has a threshold temperature to change characteristics thereof, said apparatus comprising: a first laser that emits a first laser beam that has a first power; a modulator that modulates the first power in accordance with pattern data for the grayscale photo mask to produce a first laser beam of modulated power; a drive section that moves said first laser beam of modulated power over a surface of the glass material; and a second laser that emits a second laser beam onto the glass material, the second laser beam having a second power that generates heat less than an amount capable of causing said glass material to reach said threshold temperature; and a laser control section that controls the first laser and the second laser such that (i) said second laser begins to emit the second laser beam before said first laser begins to emit the first laser beam, (ii) thereafter the glass material is simultaneously exposed to both the first laser beam and the second laser beam, and (iii) a total power of the first laser beam of modulated power and the second power generates heat that is greater than or equal to the amount capable of causing said glass material to reach said threshold temperature, wherein said glass material has a front side and a back side opposing one another, said surface having a first surface portion on said front side and a second surface portion on said back side, said first laser beam impinging on said first surface portion to form a first laser spot and said second laser beam impinging on said second surface portion to form a second laser spot, and said first laser spot and said second laser spot overlapping with one another.