Feedback-controlled laser fabrication of micromirror substrates

Abstract

Short (40-200 μs) single focused CO(2) laser pulses of energy ≳100 μJ were used to fabricate high quality concave micromirror templates on silica and fluoride glass. The ablated features have diameters of ≈20-100 μm 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 (≈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.

A small mode volume tunable microcavity: Development and characterization

“…13,14 We use an RF-pumped CO 2 -laser with wavelength 10.6 lm operating at a repetition rate of 20 kHz. A typical duty cycle of 8% results in an average output power of 7.8 W. The light is diffracted by an acousto-optic modulator, which allows sufficient control over the incident power and pulse train length in the first order diffracted beam.…”

Decoupling Path Following and Velocity Profile in Vision-Guided Laser Steering

“…6. To do so, we perform a local search around the predicted curvilinear abscissa s k given by s k +T e =ṡT e + s k (14) with T e the sampling period on Γ. This allows us to avoid searching through all the curve and be caught in ambiguities when, for instance, the path cross itself.…”

“…There are several works reported in the literature, especially in vision-based control supervision of welding process [8] or trajectory tracking (with low curvature) using a robotic arm, which embeds the laser source [9]- [11]. In addition, regular and precise path following could find applications in 2-D/3-D laser microma- chining (e.g., microsystems fabrication) [14], as well as in freecontact micromanipulation techniques (e.g., laser trapping) [15]. Yet, as far as we could understand it, all those work use trajectory tracking instead of path following, making the longitudinal controller blind to variations in laser-matter interaction.…”

Solid optical ring interferometer for high-throughput feedback-free spectral analysis and filtering

“…20 The FPI can reach sub-kHz resolution 21 and, with the help of microscopic mirrors, the instrument's free spectral range (FSR) can easily exceed 10 THz. 22,23 Nonetheless, the FPI also comes with numerous drawbacks, such as high feedback to the source, stringent mode-matching requirements, and expensive long-term stabilization needs. 24 Yet, a great variety of modern experiments in quantum optics require high-throughput filtering, often bandwidth-tunable, with frequency stability ranging from hours to days.…”