Erzeugung von periodischen Subwellenlängen-Strukturen und Wellenleitern in Dielektrika mit Laserstrahlung ultrakurzer Pulsdauer

Waveguides for optical radiation and nanostructures are essential for new and future optical technologies. The generation of waveguides with femtosecond laser radiation by moving a focus is exemplarily demonstrated with longitudinaly written volume waveguides and ridge waveguides in thin films. Combining element of both waveguide types are periodic subwavelength structures on the surface (ripples, germ. Riffel, also laser induced periodical surface structures (LIPSS)) and in the volume (nanoplanes). The subwavelength ripples emerging at ablation with ultra short pulsed laser radiation are investigated in-depth in theory and experiments as well as their influence on the structure precision and their analogy with nanoplanes. The volume waveguides in fused silica (length 9mm, diameter 1-5µm) are homogeneous and continuous at fluences below ~5kJ/cm³. Homogeneous monomode waveguides with a refractive index change Delta-n up to 2.8*10^(-4) and a damping below 2dB/cm are demonstrated. The generation of surface ridge waveguides (pulse duration t=100fs, wavelenth l=800nm and 400nm, NA 0,55, width 100µm in a 1µm thick thin film of Er:ZBLAN on magnesium fluoride) are demonstrated. Due to ripples the orientation of the polarisation is essential. The achieved smoothness of the edges is 100-300nm at a grove depth up to 1.8µm. A damping below 5dB/cm is demonstrated and the possibility of a damping below 1dB/cm is indicated. To complement the established models for classical ripples for the explanation of subwavelength ripples at pulse durations below a few nanoseconds some valuations are made such as the influence of longitudinal fields at tight focusing, near field scattering including resulting field enhancements and the significance of surface plasmons. For the first time it is suggested that for the modelling of the ripple spacing the dynamic variation of the dielectric function during the irradiation has to be taken into account. From the surface plasmon model constraints are elaborated for the real and imaginary part of ...