During the development of an optical system, one comes to the point where you have to build the optically active element into a mechanical device that becomes part of the system. At this point you come across the well-known question that it is not only necessary to consider and ensure the quality of the individual element. It is also important to look at the entire component in order to identify potential influencing factors on the performance of the optical system. At the beginning of a two-year project at Technologiecampus Teisnach the polishing process of a nonlinear crystal as the crucial component of the optical system was being explored. This system is designed to create continuous wave laser beams in the deep UV range. The crystal has to be embedded between two prisms. Roughness and shape of the crystal is ensured via the polishing process which alone has many influencing factors and was examined at the beginning of the project. The quality of the crystal can be as good as it can be, but if the contacting prisms do not fit, the whole prism-coupled device will become unusable in the overall optical laser system. The performance of the laser can only be achieved by harmonizing all elements of the PCD and the PCD itself into the laser set-up. In the current phase of the project this question will be dealt with. The prism-coupled device is split up into its individual parts, which are the nonlinear crystal, the prisms as optical auxiliary components, micro screws and mechanical support. Going through the requirements to the properties of the crystal and their limitations, the influence of the PCD on the optical performance of the crystal is presented. Here, the main focus is placed on the mode of fixing the crystal between the prisms and on putting the stack of crystal and prisms in the laser beam. The influencing factors between the crystal, the prisms and the method of fixing the PCD are described.