Fraunhofer ILT is working together with the Chair for Laser Technology of RWTH Aachen University to develop a VUV frequency comb for the optical excitation of the isomer transition. This VUV frequency comb will be used to search the transition and later to operate a nuclear clock with 229-Thorium ions in a Paul trap at LMU Munich. This requires a large power per comb mode and narrow comb linewidth, well above the state of the art. The system will be based on resonator-assisted high-harmonic generation in a gas target with a driving infrared frequency comb. 
In order to scale the VUV power, a high-power femtosecond amplifier will be used and combined with a nonlinear pulse compression scheme suitable for this particular pulse energy range. This scheme is based on a multi-pass cell and was developed at Fraunhofer ILT. Special attention has to be payed to perserve the comb properties.