Impressive though the success story of semiconductor lasers has been, there are still several spectral "gaps", wavelengths that cannot be directly accessed with laser diodes. However, nonlinear frequency conversion techniques can be employed to generate tunable laser radiation in the UV, blue and green spectral range. TOPTICA offers state-of-the-art laser systems based on second harmonic generation (SHG), sum frequency generation (SFG) and fourth harmonic generation (FHG).