Photoablation and lens damage from fractional Talbot images of Dammann gratings

Abstract

UV photoablation of materials is recorded for both the near and far fields after transmission through a Dammann grating. The fused silica Fourier lens used for far-field imaging was damaged by a near-field intensity pattern with the same periodicity as the Dammann grating. The lens was located inadvertently at one eighth of the Talbot distance Z (T) behind the Dammann grating. Patterns recorded in copper film at the even-fractional Talbot planes compare qualitatively with calculated intensities. On the basis of these findings, a near-field intensity pattern was used to ablate vias in copper and polyimide films. The pattern at a distance of Z(T)/8 was used for via ablation because it is the pattern with the most fluence per spot.