We present a novel optical system for fiber coupling of a commercial high power diode laser stack and the application of
this laser system to transmission welding of engineering thermoplastics. The diode laser stack is made up of two 20% fill
factor bars, emitting at 808 nm and with a total maximum output power of 120W CW. The stack was collimated using
FSAC micro-optics lenses in the fast and slow axis, with a full angle divergence of <4mrad and <25mrad respectively.
The optical design and simulations were carried out using ZEMAX®. Based on the design we built an optical set up,
which is divided in two subsystems. The first one collimates the laser beam in order to achieve the best focus and couple
it into the 400μm core fiber with NA0.22 and 70% efficiency. The second subsystem is designed for beam conformation
after the fiber output, using collimation and beam shaping to have a Gaussian beam profile on the work piece. The laser
system was applied to study the welding of polycarbonate plastics, based on the effects of selected welding parameters
on the seam geometry and surface integrity. The quality of the spot welding has been analyzed obtaining welded seams
with a mean diameter about 500-600μm, preserving the good technological properties of the thermoplastic considered in
this work. The results show that we have successfully developed a novel laser system which is highly efficient for
A technique for localised damage repair of fused silica optical surfaces has been investigated. The study reports the use of a CO<sub>2</sub> laser system at 10.6&mu;m wavelength with 50&mum spot diameter (measured at 1/e2) and pulse duration ranging from 50&mu;s to 200ms. Data of the threshold axial irradiance for the onset of measurable mass loss were produced and compared with heat flow calculations based in "hot" properties of silica, showing a changeover from predominantly 1-d cooling below 300µs to quasi-steady-state 2-d cooling beyond 1ms. Typically, irradiances of about 90% of the threshold for mass loss are then used. Surface melt spots generated with a single laser pulse are found to produce measurable cleaning of the initial polishing swirls and light scratches (~tens of nm deep) at all pulse lengths investigated. A reproducible reference scratch of 1.5&mu;m width and 100-200nm depth made by diamond scribing has been used to simulate smoothing or closing of crack-like features. To fully remove the test scratch requires multiple applications of long pulses. Finally, smoothing of the groups of micron-size surface pits caused by optical damage has been obtained, removing significantly the relative amplitude at high frequencies of the fast Fourier transform with a lower limit of 200 cycles/mm for the 50&mu;m spotsize.