Fundamental properties of mode-locked semiconductor disk lasers and their development towards sources for large mode spaced frequency combs.

For frequency combs the advantage of large mode spacing has become apparent due to the simplicity of isolating individual modes and the power per mode. Vibronic crystal lasers can reach this operating regime but are susceptible to Q-switching instabilities.

Mode-locked VECSELs have nanosecond upper state lifetimes and can produce sub-100-fs pulses at repetition rates between 1 and >100 GHz. They are also capable of continuous repetition rate tuning over ranges exceeding a factor of two.

Here I will discuss some of the challenges set by the semiconductor dynamics, and our approaches to tackle these, to develop VECSELs with multi-Watt average power and ~100 fs pulse durations for coherent supercontinuum generation.