In laser drilling, one challenge is to achieve a high drilling quality in high aspect ratio drilling. Ultra-short pulsed lasers use different concepts like thin disks, fibers and rods. The slab technology is implemented because of their flexibility and characteristics. They bring together both advantages and deliver high pulse energies at high repetition rates. Materials with a thickness > 1.5 mm demand specialized optics handling the high power and pulse energies with adapted processing strategies, integrated in a machine setup. In this contribution, we focus on all the necessary components and strategies for drilling high precision holes with aspect ratios up to 1:40.
A novel designed x-ray CT scanning geometry is proposed. Composed of a specially designed tungsten collimation mask
and a flat panel detector, which is placed inside the mask, this scanning geometry provides high efficient data acquisition
allowing dose reduction potential by a factor of two.
In recent years a first prototype of the CTDOR geometry (CT with Dual Optimal Reading) has been evaluated. It
consisted of a discontinuous ring of detectors fixated on X-Ray absorbing material. The source and an outer detector
were mounted on a gantry rotating around the inner static detector and the patient. Despite many drawbacks, resulting
images have shown promising potential of dual reading. Based on those results, the present work presents further
development and improvement of the recommended scanner geometry. The main idea consists of collimating the X-ray
beam through a specially designed shielding mask thereby reducing radiation dose and structuring data without
compromising image quality. An especially developed high precision laser-beam cutting process assures an accurate
mask crafting with tungsten shielding and window sizes of 300μm.
Additionally, simulation data were obtained with Monte Carlo calculations to test the dose reduction potential of the
scanning device. Retaining advantages of the CTDOR geometry such as 3D-capability, built-in capacity of scatter
correction and radiation structuring, a high-precision manufactured collimation mask of novel designed CT-scanner
enables high resolution images for breast-imaging in low energy ranges.
Laser drilling has become a valuable tool for the manufacture of high precision micro holes in a variety of materials. Laser drilled precision holes have applications in the automotive, aerospace, medical and sensor industry for flow control applications. The technology is competing with conventional machining micro electro-discharge machining in the field of fuel injection nozzle for combustion engines. Depending on the application, laser and optics have to be chosen which suits the requirements. In this paper, the results achieved with different lasers and drilling techniques will be compared to the hole specifications in flow control applications. The issue of geometry control of high aspect ratio laser drilled holes in metals will be investigated. The comparison of flow measurement results to microscopic hole dimension measurement show that flow characteristics strongly depend on cavitation number during flow.
The excimer laser provides the necessary optical resolution and sufficiently high fluence to permit rapid micro- structure patterning of polymers and glasses by ablation. Micro-scale gratings and structures formed in this way have potential applications in the fields of opto-electronic devices, display technologies and environmental sensors. Conventional broad-band excimer lasers of poor spatial and temporal coherence can be used to write sub-micron gratings with an appropriate silica phase mask in proximity mode. This simple technique has been used to fabricate fiber Bragg gratings and relief gratings on polymers. The proximity of the mask and target increases the likelihood of damage to the mask during ablation. An alternative approach using Talbot re-imaging is attractive as the mask can be remote from the samples and undesirable orders are rejected. We describe the design of a Talbot interferometer in which the zero and first order beams from a grating are recombined and experiments using this with 193 nm ArF laser illumination to form submicron gratings on polymers and in fibers.
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