Absorption of pulsed CO2 laser in silicon and resulting laser ablation and surface damage formation

The fluence dependence of the absorption of TEA CO₂ laser in silicon wafers at various dopant concentrations has been studied. The transmittance decreased with increasing fluence, and the effect of the dopant concentration was found to be small. The time profile of the pulse intensity after transmitting through a sample showed a narrowing of the width. The results indicate a buildup of photo-induced absorbance in the middle of a pulse, leading to the absorption of the later part of the pulse, and also suggest that this effect is insensitive to the ground state absorbance of the silicon samples.