Adaptable intensity distributions and parallelization of laser beams are of interest to enhance the processing efficiency for more and more laser applications. The parallelization of laser beams based on beam splitting diffractive optical elements (DOE) and a 2D galvanometer scanner is state of the art. The use of a beam splitting DOE in combination with a 2D galvanometer scanner introduces problems that need to be overcome to achieve a satisfactory result: a scanner-induced distortion of the DOE-generated spot matrix occurs in the working plane and the spot matrix twists as a function of the deflection angle of the scanner mirrors. Common setups employ either static relay lenses for multi-beam systems or additional actuators to increase spot position accuracy. We combine these two approaches in a cascaded optical system using a dynamically rotatable DOE. The achievable accuracy is evaluated with a simulation tool developed specifically for a typical optical configuration for multi-beam laser materials processing. In addition, a first functional prototype with a rotating DOE is demonstrated. The cascaded rotating DOE offers potential for flexible parallel laser processes.
We present an optical design for the illumination of a resin from different angles with UV and visible light. At the intersection of both wavelengths the resin solidifies, which is applied in volumetric 3d-printing.
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.
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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