Juergen Koch

Toward nanostructuring with femtosecond laser pulses

The development of a simple laser-based technology for the fabrication of two-dimensional nanostructures with a structure size down to one hundred nanometers is reported. The ability to micro- and nano-structure is very important for the fabrication of new materials and multifunctional microdevices. Photolithographic technologies can be applied only for plane surfaces. Using femtosecond laser pulses one can fabricate 100 nm structures on arbitrary 3D-surfaces of metals and dielectrics. In principle, the minimum achievable structure size is determined by the diffraction limit of the optical system and is of the order of the radiation wavelength. However, this is different for material processing with ultrashort laser pulses. Due to a well-defined threshold character of material processing with femtosecond lasers one can beat the diffraction limit by using tightly focused femtosecond laser pulses and by adjusting laser parameters slightly above the processing threshold. In this case only the central part of the beam can modify the material and it becomes possible to produce sub-wavelength structures. In this presentation, sub-wavelength microstructuring of metals and fabrication of periodic nanostructures in transparent materials are demonstrated as promising femtosecond laser-based nanofabrication technologies.

Lithography by maskless laser direct writing

Conventional lithography by laser mask projection has several drawbacks in terms of flexibility and costs which result in its use only for mass production. Small batches can be processed more easily and cost effectively by using direct laser writing. Laser direct writing of resists and direct laser photopolymerisation can be used to achieve small structure sizes at acceptable costs. Depending on the strategy, also several processing steps can be skipped compared to the conventional mask exposure method. The paper describes advantages of the maskless laser lithography.Conventional lithography by laser mask projection has several drawbacks in terms of flexibility and costs which result in its use only for mass production. Small batches can be processed more easily and cost effectively by using direct laser writing. Laser direct writing of resists and direct laser photopolymerisation can be used to achieve small structure sizes at acceptable costs. Depending on the strategy, also several processing steps can be skipped compared to the conventional mask exposure method. The paper describes advantages of the maskless laser lithography.

Nanostructuring of solids with femtosecond laser pulses (Keynote Address)

Investigations of possibilities for nanostructuring with femtosecond laser pulses of different materials are reported. The aim is to develop a simple laser-based technology for the fabrication of two- and three-dimensional nanostructures with structure sizes on the order of several hundred nanometers. This is required for many applications in photonics, for the fabrication of photonic crystals and microoptical devices, for data storage, displays, etc. Sub-wavelength structuring of metals by direct femtosecond laser ablation is performed. The band gap dependence of the minimum structure size for transparent materials is identified.