Time-resolved investigations of laser-matter interaction processes in dielectric coatings and bulk silica leading to laserinduced damage were performed with high temporal and spatial resolution. Distinct excitation geometries were used to study different aspects of laser matter interaction. Samples were irradiated at the pump fluence levels below and above their single shot laser-induced damage thresholds. The obtained results provide new insights about the sequence of interdependent processes. The fundamental differences between the so called 1-on-1 and S-on-1 damage morphologies are observed and discussed. New data of numerical simulations revealing the nonlinear properties of optical thin films are presented. Increased visibility in time resolved damage detection as well as observation of coherent oscillations in measured signals are introduced and discussed.
An imaging of strongly excited thin film dielectric coating is done by the means of femtosecond time-resolved off-axis
digital holography (TRDH). Ta2O5 single layer coating have been investigated at different time moments in transmission
mode. The evolving damage process was recorded in series of microscopic amplitude and phase contrast images.
Different processes were found to occur and namely: Kerr effect, free-electron generation, ultrafast lattice heating and
shock wave generation. The trends in electronic contribution are qualitatively reproduced by the theoretical model while
the other effects require additional studies.
Uniform irradiance distribution of laser spot is highly advisable in various micromachining techniques like scribing, PCB and Through-Silicon Via (TSV) drilling, repair techniques in display making technologies. Scanning over whole working field with using popular 2- and 3-axis galvo mirror scanners is another important part of microprocessing systems. Therefore, combining of beam shaping optics, converting Gaussian to flattop (uniform) laser beam profile, with scanning optical heads is an insistent technical task. To provide flattop irradiance profile it is suggested to apply field mapping refractive beam shaping optics πShaper being characterized by some important features: low output divergence, high transmittance, extended depth of field, capability to work with TEM00 and multimode lasers, as result providing a freedom in building various optical systems. De-magnifying of flattop laser beam can be realized with using imaging technique; the imaging optical system to be composed from F-theta lens of scanning head and additional collimating system to be used right after a πShaper. One of the problems in this approach is implementation of compact design of the collimating part. As a solution it is suggested to apply a specially designed Beam Shaping Unit (BSU) to be installed between a laser and a scanning head and providing: conversion from Gaussian to flattop laser beam irradiance profile, compact collimator design, and functions of laser beam adjustment and adaptation to a laser and a scanning head used in particular equipment. There will be considered design features of refractive beam shapers πShaper and BSU, examples of optical layouts to generate flattop laser spots, which sizes span from several tens of microns to millimetres. Examples of real implementations and results of material processing will be presented as well.