| Summary: | Ultrafast pulses can now be generated in mode-locked vertical external-cavity surfaceemitting lasers (ML-VECSELs) at high powers and GHz repetition rates. This laser platform has also demonstrated the addition of intracavity elements and flexibility of cavity geometries. In this thesis, we report the demonstration of two versions of repetition rate tunable VECSELs. The first, produced 215-fs pulse trains of up to 20 mW for a continuously tunable repetition rate between 0.880-1.880 GHz, directly emitted by the VECSEL. The second, produced 300-fs pulses at average powers of 50 mW, and able to tune the pulse repetition rate from 0.960-1.720 GHz. These VECSELs pave the way to performing frequency domain analysis in the GHz by resonantly exciting a sample under study. Here we have designed time-domain and frequency-domain experiments to characterise the acoustic behaviour of mechanically responsive nanostructures. The VECSEL also provides a stable platform for fs pulse generation, with a high Q-factor cavity making it possible to harness the large intracavity power. In this thesis we describe the first demonstration of a semiconductor saturable absorbing mirror (SESAM) coated with a patterned mask addition of an intracavity photoconductive antenna (PCA).
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