We demonstrate a technique for collimating conduction-cooled QCW diode laser stacks that achieves very high
brightness in a compact and robust package. First we collimate the bars in the fast-axis using a pre-aligned array of
Doric GRIN cylindrical lenses, where each lens is oriented to correct the gross positioning errors of each bar. We then
measure the residual beam errors using a proprietary wavefront mapping system, and fabricate a refractive wavefront
correction phaseplate to effectively flatten the wavefront. The type of lens used exhibits particularly low aberration in
the presence of misalignment, ensuring that the resultant wavefront can be effectively corrected. We applied the
technique to two 0.5 mm pitch, 12-bar stacks operating at 1.2 kW. By this method, we repeatably obtained a 10-fold
increase in stack brightness, reducing fast-axis beam divergence for the entire stack to below 0.3°, close to the theoretical
limit. The result is an extremely compact, high brightness source optimised for side-pumping thin slab lasers.
Ultrashort-pulse single-maximum nondiffracting beams of microscopic radius and large axial depths are interesting for applications in nonlinear optics and spectroscopy, for acceleration and manipulation of particles, measuring techniques, materials treatment or information processing. Here we report on the experimental generation of such beams by self-apodized truncation of Bessel and pseudo-Bessel beams from a Ti:sapphire oscillator. Small angle operation was enabled by thin-film structures. To obtain self-apodization, the diameter of the truncating diaphragm was adapted to the first minima of Bessel distribution. The propagation of (a) Bessel beams of meter-range axial extension shaped by axicon mirrors, and (b) microscopic pseudo-Bessel beams of millimeter-range extension shaped by Gaussian-shaped microaxicon lenses was studied. In case (a), single-maximum beams of > 20 cm depth were produced. To generate comparable focal zones from Gaussian beams, a much larger distance (10x) is necessary, and axial stretching of spectrum destructs the temporal structure. In case (b), the focal zone length was increased by a factor of >5 compared to a Gaussian beam. Arrays of truncated Bessel beams were generated as well. The experimental results indicate that truncated Bessel beams enable more compact setups than corresponding Gaussian beams and are in particular advantageous for ultrashort pulses. Further improvements are possible by combining coherent addition in resonators with truncation outcoupling.