Bachelor defense by Jasmin Lehmkuhl Wænnerstrøm

Optimization of IR incoupling to SFG cavity - Towards light generation for laser manipulation of germanium

To investigate a particular transition of interest in germanium, a coherent light source at 209 nm is required. The source should be of high intensity due to germaniums large saturation intensity. This thesis aims at facilitating the generation of this light by sum frequency generation (SFG), and the main focus of the thesis is the 922 nm light source, to be summed with 271 nm inside a bowtie cavity. The 922 nm laser has been beam shaped, fiber coupled and mode matched to a SFG cavity. The cavity stabilization is based on the Hänsch-Couillaud method. A fiber coupling efficiency of ≈ 66% has been achieved. The cavity was characterized by scanning its length, yielding a finesse of F ≈ 144 ± 3, and the incoupling efficiency into the TEM₀₀ mode was determined to be (32 ± 2) %. Stable locking of the cavity was prevented by polarization drift in the PM fiber. These results indicate that improvements to beam shaping, fiber coupling and mode matching are required before cavity lock is a possibility and sufficient 209 nm light can be generated.