Pulsed laser machining and polishing of silica micro-optical components using a CO₂ laser and an acousto-optic modulator

Laser ablation and laser smoothing of silica is investigated as a method of manufacturing custom micro-optics for use with high-power, diode laser arrays. A highly flexible machining regime has been identified that uses 30 to 60 µs square pulses, generated from a stabilised CO₂ laser by an acousto-optical modulator (AOM). Refractive optical surfaces with apertures of 1 mm × 1 mm have been generated by the multi-pulse, raster scanning method with cut depths in the range of 10 to 30 µm controlled to an accuracy of better than 150 nm. A subsequent laser "fire polishing" step to smooth out the surface, using the same laser system as for machining, but in a long pulse mode at an energy fluence that just avoids further ablation of the surface. The objective of the research is to produce rapid prototyping of arrays of refractive elements, to avoid the tooling or mask-writing steps of alternative methods. A particular interest is in the generation of corrective optical elements to improve the beam quality of arrays of diode laser bars.