Although excimer and ultrafast laser technology can machine silica glass, the high average power and material removal rate of CO2 lasers is more practical for machining large surface areas, provided that feature sizes are greater than 10 µm. Conventional CO2 configurations, however, create surface roughness by molten material ejection or displacement of irradiated glass.Researchers at Heriot-Watt University in Edinburgh, UK, have reported an approach to laser-machining silica glass by ablation that uses an acousto-optical modulator to shape the output of a CO2 laser. They demonstrated that rectangular pulses with widths of 30 to 50 µs allowed greater control over the ablation process, with material evaporating smoothly from the surface at temperatures of about 3000 °C. By avoiding melt ejection or melt displacement, the technique produced machined silica with improved surface smoothness.The researchers describe their system and experimental results in the Sept. 20 issue of Applied Optics.