The high demand for beam shaping technology by the display industry has lead to higher resolutions, smaller pixel pitch
and reduced costs. Nowadays high quality, nematic Liquid Crystal on Silicon microdisplays (LCoS) with resolutions of
1920 × 1080 pixels and 8 μm pixel pitch are available. The optical properties of these microdisplays allow for their
application as an adaptive optical element where instantaneous change between arbitrary beam profiles is necessary.
Laser material processing which often requires high beam qualities with various beam profiles is one industry where this
technology could be applied. In this paper, a compact beam shaping setup and simple characterization methods for
practical use of the LCoS at micromachining stations are presented.
Observation of defects inscribed in 3D photonic band gap opal templates has been investigated by means of
fluorescence of solidified photo polymer. The defects, or breaks in periodicity, have been inscribed inside the structure
by two-photon polymerization (2PP) of an infiltrated hybrid polymer from the type ORMOCER®. In-situ and ex-situ
observation of the inscribed defects has been achieved with fluorescence microscopy.
Infrared, femtosecond laser pulses are ideal for the fabrication of 3D structures in transparent media. Due to the low
absorption cross-section, 2 or more photons are necessary for absorption. This multi-photon effect limits the affected
volume to the focal area allowing for sharp features on the order of the wavelength of light. One possible multi-photon
reaction is the photo-destruction (ablation, decomposition, etc.) or photo-polymerization of materials. Using these
techniques, 3D photonic components can be realized.
A photonic band gap template has been created with a monodisperse polystyrene (PS) spheres (diameter ~ 624 nm).
We have used ultrafast laser pulses to remove spheres (introduce defined defects) at the surface to gain a fuller
understanding of the laser-material interaction. To optimally focus inside the bulk, an index matching material must be
infiltrated. By using a photosensitive material, two-photon polymerization can be used to harden the material
surrounding the spheres and insert defects inside the bulk. With proper placement of defects, 3D photonic components,
i.e., waveguides, splitters, and filters, can be created.
Tight focusing of ultrashort near infrared laser pulses in the bulk of various transparent materials induces significant modifications of the optical properties by locally changing the material refractive index. Such laser-induced phase objects are of major technological interest, notably for direct writing of embedded optical functions. While extensive studies have been reported on ultrashort pulsed laser induced modifications in several materials, especially with regard to focusing conditions, incubation effects, or the influence of the energy content of the pulse, we emphasize here the role of the temporal design of the excitation sequence. We present phase-contrast microscopy investigations of the resultant morphology and discuss the refractive index topological map induced by different temporal pulse intensity envelopes in various transparent materials. The consequences of temporal profiles generated by a pulse shaping apparatus on the morphology of the interaction zone are illustrated, emphasizing the benefits of the synchronization between the excitation temporal profile and the material response.
Phase manipulated ultrafast laser pulses and temporally tailored pulse trains with THz repetition rates are promising new tools for quality micromachining of brittle dielectric materials, allowing to adapt the laser light to the material properties for optimal processing quality. Different materials respond with specific reaction pathways to the sudden energy input depending on the efficiency of electron generation and on the ability to release the energy into the lattice. Loss and cooling mechanisms in the electron population, surface charging, as well as the strength of the electron-phonon interactions control the effectiveness of the energy deposition into the lattice. Knowledge of the response times of materials establishes a guideline for using temporally shaped pulses or pulse trains in order to optimize the structuring process with respect to efficient material removal and reduction of the residual damage. The sequential energy delivery with judiciously chosen pulse trains may induce softening of the material during the initial steps of excitation and change the energy coupling for the subsequent steps. We show, that this can result in lower stress, cleaner structures, and allow for a material-dependent optimization process.
A significant improvement in the quality of ultrafast laser micromachining of brittle dielectrics is demonstrated by using temporally shaped pulse trains with sub-ps separation, synchronized with the material specific relaxation times. The individual material response to laser radiation depends on the efficiency of electron generation and on the ability to release the energy into the lattice. Loss mechanisms in the electron population, surface charging, as well as the strength of the electron-phonon interactions control the effectiveness of the energy deposition into the lattice. Knowledge of the response times of materials establishes a guideline for using temporally shaped pulses or pulse trains in order to optimize the structuring process with respect to the efficiency of material removal and reduction of the residual damage. The sequential energy delivery induces a material softening during the initial steps of excitation changing the energy coupling for the subsequent steps. This leads to lower stress, cleaner structures, and provides a material-dependent optimization process.
Dielectric materials exposed to ultrashort laser radiation have evidenced individualized paths to deposit the energy into the lattice. Electronic and thermal mechanisms competing in the process of material removal depend on the efficiency of the electrostatic energy accumulation on the surface due to photoionization, as well as on the lattice heating which follows the electron-phonon coupling. The electrostatic surface break-up is a fast, sub-picosecond process, while thermal mechanisms start to dominate on a longer, picosecond time scale given by the electron-lattice equilibration and phase transformation time. The Coulomb- explosion induced ion ejection due to surplus charge accumulated on the surface during the photoionization process is significant only in dielectrics while in semiconductors and metals an efficient neutralization occurs. The significance of the different channels in dielectric materials can be reduced or enhanced by using laser pulses which are modulated on a time scale characteristic for the above mentioned mechanisms. Thus, amplified temporally-shaped pulses, double peaks, or pulse trains with a separation below 1 ps can have a significant effect on the quality of micromachining of transparent materials. The energy deposition can be modulated in such a way that the first pulse of properly chosen energy leads to a softening of the material associated with the onset of heating, thus changing the coupling conditions for the next pulses. This leads to less residual stress accumulation, cleaner structures, and opens the way for a material dependent optimization process.