The paper entitled “100 W average power femtosecond laser at 343 nm” recently has been selected as a “spotlight on photonics” paper by the optical society of america (OSA). The authors, a collaboration between the Helmholtz-Institute-Jena (HIJ), the Institute of Applied Physics (IAP), the Fraunhofer Institute of Applied Optics and Precision Engineering (IOF) and the Institute of Photonic Technology (IPHT), achieved a significant improvement of the beam quality of a high power femtosecond UV laser. By contacting sapphire heat spreaders to the nonlinear crystals they efficiently mitigated thermo-optical effects and beam distortions. With this technique a record-high average power of 100 W was demonstrated with femtosecond pulses at 343 nm wavelength. In future, such lasers will advance many applications ranging from industry up to fundamental science.