A study on ultrafast laser Bessel beam processing and laser confocal in-situ measurement method

In-situ geometric morphology measurement of samples during ultrafast laser processing is crucial for achieving precision processing. This study proposes a novel method for in-situ measurement in ultrafast laser Bessel beam processing by coupling ultrafast laser Bessel beam processing technology with laser confocal technology at the focusing objective, and a hybrid system is developed based on this method. The ultrafast laser Bessel beam processing technology facilitates micro-precision processing of the sample, while the bilateral fitting subtracting laser confocal technology offers high axial focusing precision and lateral resolution, achieving initial spot focusing and in-situ geometric morphology measurement of the sample. Theoretical analysis and experimental validation demonstrate that the incident light, after passing through the axicon lens and the telescope system (f₁ = 250 mm, f₂ = 18 mm), generates a Bessel beam with a central lobe radius of approximately 1.83 μm and a maximum non-diffractive propagation distance of 1.43 mm. The lateral resolution of confocal microscopy imaging is better than 800 nm. Ablation microholes and cutting experiments conducted on 0.72 mm thick fused silica substrates demonstrate the system's capability to achieve high-resolution geometric morphology imaging of ablated microholes and precise cutting of fused silica. This study offers a novel methodology and theoretical foundation for realizing micro-precision processing and in-situ geometric morphology measurement of samples.