Ms. Nicole Grubert Profile

Nicole Grubert

at RWTH Aachen University

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Proceedings Article | 15 March 2023 Presentation + Paper

Fiber-based sensor for combustion chamber monitoring: manufacturing challenge

N. Grubert, M. Prochnau, J. Stollenwerk, C. Holly

Proceedings Volume 12434, 124340O (2023) https://doi.org/10.1117/12.2647501

KEYWORDS: Combustion, Sensors, Optical sensors, Fiber optics sensors, Manufacturing, Spatial resolution, Optical components, Laser damage threshold, Data acquisition

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The measurement of relevant process emissions is a challenging task, especially when access for measurement technology is limited. One example is the optical combustion chamber monitoring of internal combustion engines. The access is limited and spatial resolution for observation is limited by the possible use of optical elements in the combustion chamber. So far, data acquisition has been realized with the aid of spark plugs with integrated connections to an optical sensor. This optical spark plug has the function of a spark plug and simultaneously enables the detection of light in the engine. The optical spark plug is positioned in the center of the combustion chamber which allows for a symmetrical design for a 360° field of view. Our approach is to build an alternative fiber-based light sensor without the function of a spark plug, because if no ignition unit is installed, there is more space for additional optical elements for higher optical spatial resolution than conventional light sensors with ignition function. The main challenge is the miniaturization of the optical and mechanical set up. Due to the fixed position of the spark plug and the limited access to the combustion chamber, the light sensor must be inserted at an angle into the combustion chamber at a different location, so, the optical system must be asymmetric. This paper presents the results of the design and fabrication of a combustion chamber light sensor with respect to the optical and mechanical challenge of spatially resolved detection of light pulses in a combustion chamber of an engine under an oblique access to the combustion chamber.

Proceedings Article | 3 October 2022 Paper

Beam shaping for large-area laser structuring in a roll-to-roll process

N. Grubert, O. Hofmann, M. Hesker, J. Stollenwerk, C. Holly

Proceedings Volume 12216, 1221604 (2022) https://doi.org/10.1117/12.2632926

KEYWORDS: Diffractive optical elements, Beam shaping, Axicons, Optical design, Laser ablation

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Laser structuring is a powerful tool for functionalizing surfaces, e.g., improving the tribological properties. To achieve small structures in the < 2 μm range, microscope objectives are typically used in laser material processing. There are two main challenges to achieve small structures: On the one hand, the limited working distance between the focusing optics and the workpiece results in a comparatively small processing area of a few square millimeters. On the other hand, the depth of field is limited when structuring with microscope lenses due to their large numerical aperture. As a result, the intensity of the laser beam is strongly dependent on the position in the propagation direction, so that the process window for material removal is only a few μm and small deviations disrupt the process. For highly productive large-area laser structuring in a roll-to-roll (R2R) process, the processing area must be enlarged, and the depth of field must be increased at the same time to enhance process robustness. With a given R2R process speed of the moving material of 2 m/min, and a material width of 0.5 m, we want to structure an area of 1 m²/min. The structuring pattern is a hexagonal arrangement of spots with a spot diameter of 1-2 μm and a spot distance of 2 μm. Additionally, we want to achieve a depth of field of 45-50 μm to enhance the process robustness. Given this background, this paper presents an approach in which a laser beam is split into numerous sub-beams and these sub-beams are subsequently shaped in such a way that the depth of field is increased for each individual beam. For beam shaping, a combination of static optical elements is used to transform a uniform into a Bessel-like intensity distribution to achieve a greater depth of field. By a skillful arrangement of the focusing elements, structure sizes of 1-2 μm as well as structure distances of 2 μm are achieved with the given R2R process speed.

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