Antimicrobial Photodynamic Therapy

Simulation of Drilling with nanosecond Pulses. Copyright: Fraunhofer ILT Simulation of Drilling with nanosecond Pulses.

Laser-induced antimicrobial photodynamic therapy (aPDT) is already being used today on a large scale to treat mild cases of periodontal disease and as an adjunct to conventional mechanical or anti-infective therapies. Under irradiation of laser light, light-sensitive dye creates the highly-aggressive singlet oxygen, which destroys disease-causing bacteria. In order to tap the potential of this treatment, scientists need to clearly understand the underlying physical and biochemical processes. To enable that, mathematical-physical modelling is necessary. In particular, this includes mathematical and physical modelling of how laser radiation propagates in strongly scattering biological tissues (e.g. periodontium) and what the kinetics are of the photochemical reactions occurring there. The group is aiming to build a dynamic, spatially distributed model to analyse and interpret aPDT. This approach will enable physicians to monitor therapeutic progress.



Ripples formation at the cutting edge. Copyright: Fraunhofer ILT Ripples formation at the cutting edge.

Cognition, Intelligent configuration and systematic error diagnosis for maintenance are technical applications on the path to realising the vision of a virtual and cognitive cutting machine. With the virtual cutting machine, developments in cutting processes will be advanced to the physical limits of the laser beam, machine and process, all with a defined level of quality. The combination of diagnosis and simulation yields a systematic definition of the relationships between cut quality and cutting parameters. Analysis of the cut quality leads to at least three different types of ripples at the cut surfaces and four different types of burrs or adherent dross. The formation of the various ripples and dross types is described by a straightforward set of parameters, their dynamics and interactions during cutting. The formulation of inverse problems yields the information regarding advantageous beam shaping.



Simulation of Cutting. Simulation of Cutting.

The work on welding represents application and extension of the results on cutting and is as well directed toward model-based quality assurance, calculation of the welding distortion and analysis of the suitability of new laser beam sources. The dynamics of the vaporisation-driven melt flow and its effects on the seam shape, the morphology of the weld bead and the pore formation are investigated in order to identify measures for model-based quality assurance. Calculation of the weld distortion with commercially available simulation tools is not sufficiently reliable. In order to identify the reasons for the poor quality of the available simulations, the structural stability of the fundamental models is analysed and expanded with a further understanding of the dynamic processes during welding as well as a more refined handling of the thermomechanical effects.



Formation of Melt Closure during Drilling with microsecond Pulses. Copyright: Fraunhofer ILT Formation of Melt Closure during Drilling with microsecond Pulses.

Creation of models and simulation of drilling with lasers pursues primarily the following aims: avoiding recast on the drilled wall for long pulse lengths (microseconds) and increasing the drilling speed for short pulse lengths (picoseconds to nanoseconds). The analysis of drilling with long pulse lengths leads to the identification of four different phenomena that interact dynamically to cause the formation of recast on the drilled wall. For shorter pulse lengths and higher laser beam intensity, the inertia of the melt, recondensation of the vapour on the drilled wall, reflection of the beam and changing of the state equation upon nearing the critical temperature are all of importance.