# High-Precision Polishing of Fused Silica Microfluidic Chips via CO2 Laser

## TL;DR

A CO2 laser polishing method significantly improves the surface quality of fused silica microfluidic chips, achieving optical-grade smoothness.

## Contribution

A high-precision CO2 laser polishing strategy using shallow-layer melting and reflow for fused silica microfluidic chips.

## Key findings

- Defocus distance is the dominant factor affecting surface roughness, followed by scanning speed and laser power.
- Optimal parameters achieved a surface roughness of 0.157 µm at a 50% overlap rate.
- Surface roughness was reduced from 303 nm to 0.33 nm, meeting optical-grade quality requirements.

## Abstract

To address the severe surface imperfections induced during ultrafast pulsed laser fabrication of fused silica microfluidic chips, a high-precision CO2 laser polishing strategy based on shallow-layer melting and reflow was employed. This method enables localized melting within an extremely thin surface layer, effectively smoothing the topography without altering the original microstructure geometry. An L9(33) orthogonal experimental design was conducted to systematically investigate the influence of key parameters on polishing quality, identifying defocus distance as the dominant factor affecting surface roughness, followed by scanning speed and laser power. The optimal parameter combination was determined to be a laser power of 8 W, a defocus distance of 6 mm, and a scanning speed of 5 mm/s. Furthermore, an overlap rate between 38% and 63% was found to ensure sufficient fusion without excessive remelting, with the minimum surface roughness of 0.157 µm achieved at a 50% overlap rate. Based on the optimized parameters, adaptive scanning paths were designed for different functional units of a fused silica microfluidic chip. Surface characterization demonstrated that the surface roughness was remarkably reduced from 303 nm to 0.33 nm, meeting optical-grade surface quality requirements.