The two basic classes of volumetric displays are swept volume techniques and static volume techniques. During several years of investigations on swept volume displays within the FELIX 3D Project we learned about some significant disadvantages of rotating screens, one of them being the presence of hidden zones, and therefore started investigations on static volume displays two years ago with a new group of high school students. Systems which are able to create a space-filling imagery without any moving parts are classified as static volume displays. A static setup e.g. a transparent crystal describes the complete volume of the display and is doped with optically active ions of rare earths. These ions are excited in two steps by two intersecting IR-laser beams with different wavelengths (two-frequency, two-step upconversion) and afterwards emit visible photons. Suitable host materials are crystals, various special glasses and in future even polymers. The advantage of this approach is that there are only very little hidden zones which leads to a larger field of view and a larger viewing zone, the main disadvantage is the small size of the currently used fluoride crystals. Recently we started working with yttrium-lithium-fluoride (YLiF 4 ) crystals, which are still very small but offer bright voxels with less laserpower than necessary in CaF 2 crystals. Potential applications are for example in medical imaging, entertainment and computer aided design.

The FELIX 3D Display belongs to the class of volumetric displays using the swept volume technique. It is designed to display images created by standard CAD applications, which can be easily imported and interactively transformed in real-time by the FELIX control software. The images are drawn on a spinning screen by acousto-optic, galvanometric or polygon mirror deflection units with integrated lasers and a color mixer. The modular design of the display enables the user to operate with several equal or different projection units in parallel and to use appropriate screens for the specific purpose. The FELIX 3D Display is a compact, light, extensible and easy to transport system. It mainly consists of inexpensive standard, off-the-shelf components for an easy implementation. This setup makes it a powerful and flexible tool to keep track with the rapid technological progress of today. Potential applications include imaging in the fields of entertainment, air traffic control, medical imaging, computer aided design as well as scientific data visualization.The FELIX 3D project team has evolved from a scientific working group of students and teachers at a normal High School in Germany. Despite minor funding resources within this non-commercial group considerable results have been achieved.