Analytical model for CO(2) laser ablation of fused quartz.

This paper reports the development of an analytical model, with supporting experimental data, which quite accurately describes the key features of CO laser ablation of fused silica glass. The quantitative model of nonexplosive, evaporative material removal is shown to match the experimental data very well, to the extent that it can be used as a tool for ablative measurements of absorption coefficient and vaporization energy. The experimental results indicated that a minimum of 12  MJ kg is required to fully vaporize fused quartz initially held at room temperature, which is in good agreement with the prediction of the model supplied with input data available in the literature.

Locking and wavelength selection of an ultra-collimated single-mode diode laser bar by a volume holographic grating.

Wavelength-locking by a volume holographic grating (VHG) is reported for a diode laser bar with 49 single mode emitters, fitted with a dual-axis collimation phase-plate for smile elimination and excellent beam pointing correction. The much-improved VHG feedback with the ultra-collimated array beam gives 100% wavelength locking at 975 nm over a 17°C temperature range and external cavity lengths up to 110 mm. This enables a folded cavity configuration to provide a fully-locked array with wavelength selection into 200 pm channels over an 8 nm band, suitable for multi-bar dense wavelength-combining.

Femtosecond pulses at 50-W average power from an Yb:YAG planar waveguide amplifier seeded by an Yb:KYW oscillator.

We report the demonstration of a high-power single-side-pumped Yb:YAG planar waveguide amplifier seeded by an Yb:KYW femtosecond laser. Five passes through the amplifier yielded 700-fs pulses with average powers of 50 W at 1030 nm. A numerical simulation of the amplifier implied values for the laser transition saturation intensity, the small-signal intensity gain coefficient and the gain bandwidth of 10.

Generation of microstripe cylindrical and toroidal mirrors by localized laser evaporation of fused silica.

We report a new technique for the rapid fabrication of microstripe cylindrical and toroidal mirrors with a high ratio (>10) of the two principal radii of curvature (RoC(1)/RoC(2)), and demonstrate their effectiveness as mode-selecting resonator mirrors for high-power planar waveguide lasers. In this process, the larger radius of curvature (RoC(1)) is determined by the planar or cylindrical shape of the fused silica substrate selected for laser processing, whilst the other (RoC(2)) is produced by controlled CO(2) laser-induced vaporization of the glass. The narrow stripe mirror aperture is achieved by applying a set of partially overlapped laser scans, with the incident laser power, the number of laser scans, and their spacing being used to control the curvature produced by laser evaporation.

Laser smoothing of binary gratings and multilevel etched structures in fused silica.

We describe a promising approach to the processing of micro-optical components, where CO(2) laser irradiation in raster scan is used to generate localized surface melting of binary or multilevel structures on silica, fabricated by conventional reactive-ion etching. The technique is shown to provide well-controlled local smoothing of step features by viscous flow under surface tension forces, relaxing the scale length of etch steps controllably between 1 and 30 microm. Uniform treatment of extended areas is obtained by raster scanning with a power stabilized, Gaussian beam profile in the 0.

Dual-axis beam correction for an array of single-mode diode laser emitters using a laser-written custom phase-plate.

A single optical component for a diode laser bar combines fast-axis smile and lens error correction with slow-axis collimation. Produced by laser-machining/polishing, it provides 0.9 mm focal length, 200 microm pitch slow-axis collimation on the same surface that corrects fast-axis errors.

Efficient laser polishing of silica micro-optic components.

We report a study of the basic characteristics of laser polishing of fused silica with a protocol that is particularly suitable for surface smoothing of micro-optic elements fabricated by a laser ablation process. We describe a new, to our knowledge, approach based on scanning a highly controlled small size laser beam and melting areas of tens to hundreds of micrometers of glass using a computer-controlled raster scan process, which does not require beam shaping, substrate preheating, or special atmospheres. Special test samples of silica substrates with prescribed spatial frequency content were polished using a range of irradiation conditions with the beam from a well-controlled CO2 laser operating at a wavelength of 10.

Effect of vaporization and melt ejection on laser machining of silica glass micro-optical components.

A new regime for silica glass machining for micro-optical fabrication applications, which uses pulsed CO2 laser radiation in the 2.5-100-micros pulse width region that has been generated by an acousto-optic modulator, is investigated. A filamentary melt ejection process that generates fibers and significant melt displacement limits machining quality below 30-micros pulse width.