Feedback-controlled laser fabrication of micromirror substrates

Short (40-200 mu s) single focused CO(2) laser pulses of energy greater than or similar to 100 mu J were used to fabricate high quality concave micromirror templates on silica and fluoride glass. The ablated features have diameters of approximate to 20-100 mu m and average root-mean-square (RMS) surface microroughness near their center of less than 0.2 nm. Temporally monitoring the fabrication process revealed that it proceeds on a time scale shorter than the laser pulse duration. We implement a fast feedback control loop (approximate to 20 kHz bandwidth) based on the light emitted by the sample that ensures an RMS size dispersion of less than 5% in arrays on chips or in individually fabricated features on an optical fiber tip, a significant improvement over previous approaches using longer pulses and open loop operation. (C) 2011 American Institute of Physics. [doi:10.1063/1.3671291]