Uppsala University is involved in a large international collaborationto build the Laser heater system for the European Xray Free-electronlaser in Hamburg, Germany. In this thesis I describe a laser incouplingdevice into the vacuum chamber of this laser heater all the way fromthe specifications to a completed design. The laser heater is a very important part of the XFEL and thepart described here is a part of the vacuum system needed to couplean external laser into the electron vacuum system and align it withthe electron bunches in order to heat them. The task was started by studying the literature about the basic theory andthe design of vacuum systems. After this study and collection of ideaswith colleagues I started to prepare different concepts to solve thetask. The ideas can be put into two categories, in one case the couplingmirror is located inside the vacuum chamber and in the second caseoutside. The concepts were evaluated with colleagues from the physicsdepartment and one solution from each category was evaluated further. The work continued to develop and refine these concpets. During the workseveral obstacles appeared, the biggest one was that with the 'inside'concept some of the design constraints had to be disregarded, butduring further work the design was adapted and the problems weremostly solved. The concept with the mirror outside the vacuumchamber was succesfuland the design was completed. In this thesis SolidWorks was used for the design work of thedifferent concepts and all parts that are part of the icouplingelement for the XFEL laser heater. All drawings are generated inSolidWorks as well and are attached to this report.