This paper describes a new method for optimized laser treatment. One of the goals of laser bone treatment is to avoid thermal damage to the surrounding tissue. Er:YAG laser systems are suited for gentle bone treatment. The laser result depends on the laser parameters like pulse energy, pulse frequency and pulse length. Additionally, the laser result depends on the distance between the laser focus and the bone surface. This dependency is founded in the laser beam geometry. The laser beam diameter increases with increasing distance to the focus. Therewith, the energy density of the laser beam decreases with increasing distance. To point the correlation between the focus position and the laser result an experiment with pig compacta was performed and validated. The results show a dependency between the focus distance and the carbonization of the bone cavities. Furthermore, the depth of the produced cavities decreased with the focus distance. To avoid laser treatment beyond the laser focus a navigation concept is presented. Therewith, laser focus is visualized relative to image data of the treated bone tissue.