Coherence effects in surface roughness induced by vacuum ultraviolet F2 laser ablation

Area of Science:

• Laser physics
• Materials science
• Surface science

Background:

• Understanding laser-induced surface modifications is crucial for precision manufacturing.
• Statistical fluctuations in laser beam properties can impact material processing outcomes.
• Coherence effects in lasers play a role in the spatial distribution of energy.

Purpose of the Study:

• To analyze statistical fluctuations in the spatial fluence distribution of a multimode F2 laser.
• To investigate the influence of coherence effects on ablated surface smoothness.
• To predict and experimentally verify the relationship between laser pulses and surface roughness.

Main Methods:

• Analysis of pulse-to-pulse spatial fluence distribution in a highly multimode F2 laser.
• Theoretical prediction of surface roughness scaling with the number of ablation pulses (m^1/2).
• Experimental measurement of induced roughness on N-BK7 glass using a 157-nm laser and white-light interferometry.

Main Results:

• Fluctuations in laser fluence distribution are on the order of a few percent.
• Measured surface roughness on N-BK7 glass shows reasonable agreement with theoretical predictions.
• Surface roughness increases with the square root of the number of ablation pulses (m^1/2).

Conclusions:

• Statistical fluence fluctuations in multimode lasers contribute to surface roughness during laser ablation.
• The observed roughening mechanism is consistent with theoretical models.
• Coherence effects significantly influence the attainable smoothness of laser-ablated surfaces.