The CRESST Dark Matter Search aims to detect Dark Matter particles via their elastic scattering off nuclei in scintillating target crystals. A simultaneous measurement of a phonon and light signal allows to efficiently discriminate the dominant beta and gamma background from expected nuclear recoil signals. For a given light detector and reflector, it is the scintillation efficiency of the crystal which determines the lowest energy for which the active background discrimination is still efficient. Crystals with a higher light output therefore can improve the overall sensitivity of the experiment. In this context, measurements of the light yield of CsI (undoped) and CdWO 4 crystals at milli-Kelvin temperature are presented. Furthermore we report on first results of measurements of these crystals in conventional CRESST configuration.
The performance of optical systems is typically improved by increasing the number of conventionally fabricated optical components (spheres, aspheres, and gratings). This approach is automatically connected to a system enlargement, as well as potentially higher assembly and maintenance costs. Hybrid optical freeform components can help to overcome this trade-off. They merge several optical functions within fewer but more complex optical surfaces, e.g., elements comprising shallow refractive/reflective and high-frequency diffractive structures. However, providing the flexibility and precision essential for their realization is one of the major challenges in the field of optical component fabrication. In this article we present tailored integrated machining techniques suitable for rapid prototyping as well as the fabrication of molding tools for low-cost mass replication of hybrid optical freeform components. To produce the different feature sizes with optical surface quality, we successively combine mechanical machining modes (ultraprecision micromilling and fly cutting) with precisely aligned direct picosecond laser ablation in an integrated fabrication approach. The fabrication accuracy and surface quality achieved by our integrated fabrication approach are demonstrated with profilometric measurements and experimental investigations of the optical performance.
Holographic Optical Elements (HOE) are well known optical devices which can be used as for example light focusing and/or directing the light to desired areas. Until now, there have been no manufacturing facilities capable to manufacture substantial quantities of volume holographic optical elements with in-application stable properties devoted to being used as taillights or head-up displays in a relatively harsh automotive environment. We describe in this article the working principles of an industrial manufacturing process of holographic optical elements targeting automotive industry needs.
An innovative optical system for trapping particles in air is presented. We demonstrate an optical system specifically optimized for high precision positioning of objects with a size of several micrometers within a nanopositioning and nanomeasuring machine (NPMM). Based on a specification sheet, an initial system design was calculated and optimized in an iterative design process. By combining optical design software with optical force simulation tools, a highly efficient optical system was developed. Both components of the system, which include a refractive double axicon and a parabolic ring mirror, were fabricated by ultra-precision turning. The characterization of the optical elements and the whole system, especially the force simulations based on caustic measurements, represent an important interim result for the subsequently performed trapping experiments. The caustic of the trapping beam produced by the system was visualized with the help of image processing techniques. Finally, we demonstrated the unique efficiency of the configuration by reproducibly trapping fused silica spheres with a diameter of 10 μm at a distance of 2.05 mm from the final optical surface.
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