Interference ablation by ultrashort laser pulses via diffractive beam managementThursday (25.06.2020) 13:50 - 14:30 Room 2
Creating periodic patterns on the surface of technical materials find numerous applications for marking, adjusting the wettability, enhancing or lowering friction, enhancing solar cell efficiency and in many others fields. Patterns with periods ranging from a few 100 nm to a few µm are of particular interest, because they are optically effective in creating colorful surfaces. Conversely, optical methods are optimally suited to create such micron sized patterns. It is well known that interference of two or multiple coherent laser beams leads to periodic intensity patterns, which are well suited to create corresponding structural patterns on material surfaces. Such structures can be fabricated by lithographic methods, in which a photoresist is modified requiring additional processes (e.g. etching) to transfer the modification into the material to be structured. Alternatively, the laser radiation can directly affect the material surface leading to periodic modification or ablation. Main quality criteria of such patterns are a suitable aspect ratio and a high regularity of the structure. To obtain high quality, sufficient control of the interfering beams is necessary.
In this contribution an overview of various interference-based techniques for the fabrication of micro- and nano-patterns is given. Applying diffractive beam management, high definition, strictly periodic structures are obtained with a vast variety of different topologies.
The generation of the interfering beams is accomplished by diffractive optical elements like gratings, grating systems or computer generated holograms. The recombination of the diffracted beams is performed by optical imaging or diffractive beam management. Ultrashort pulses, in particular in the ultraviolet spectral range, are especially suited for generating micron- to sub-micron-sized deterministic periodic patterns on metals, semiconductors and dielectrics.
A simple phenomenological model gives a good prediction of the shape of complex patterns, which are obtained experimentally. A much more sophisticated atomistic model can even describe the structural details on the submicron level on and below the processed surface. Detailed knowledge of the structure formation and the capability to predict overall topologies provide a powerful tool for designing the surface structures for specific functionalities.