In-situ measurement of submerged micro-structures using model-based confocal fluorescence microscopy
The growing demand for technical parts with micro dimensions increasingly requires the use of manufacturing techniques such as laser chemical manufacturing (LCM), whose non-contact material removal is based on a localized chemical reaction with an electrolyte fluid. An in-situ measurement of the surface geometry using confocal fluorescence microscopy (see Fig. 1) is intended to improve the LCM surface quality. Despite the challenges of the LCM process, such as the µm structure sizes, high aspect ratios and steep edge angles of the measurement objects as well as the liquid surrounding them, this method is highly suitable for in-situ geometry measurements. The surface geometry is determined by a signal model (see Fig. 2) which is fitted to the measured fluorescence signal. Since not all influencing factors on the fluorescence signal have been identified yet, the extension of the model as well as the minimization of the measurement uncertainty is the subject of current research.
The main task of the thesis is the further development of the fluorescence signal model in order to take into account additional influencing factors such as surface reflectivity in order to reduce the measurement uncertainty of the geometry measurement. For this purpose, limits of the measurability of the indirect geometry measurement are to be determined and compared with conventional confocal microscopy. In addition, the potential of alternative illumination strategies such as oblique or lateral illumination can also be investigated.
Potential contents of the thesis could be:
- Investigation of alternative illumination strategies such as oblique or lateral excitation
- Extension of the signal model to minimize model uncertainties as measurement uncertainty sources and validation with reference samples of different surface qualities
- Determination of the measurability limits with regard to surface reflectivity and comparison measurements with conventional confocal microscopy