Semiconductor Seeded Fibre Amplified Sources of Ultra Short PulsesBy Stephen Paul ElsmereThis thesis reports upon an experimental investigation of passively mode-locked opticallypumped vertical-external-cavity surface-emitting semiconductor lasers (VECSEL).Mode-locked VECSELs are a compact source of ultra-short pulses at GHz repetitionrates, with pulse lengths as short as 190 fs being generated directly from thelaser. The VECSEL is a power scalable device offering spectral versatility throughband gap engineering of semiconductor gain material.Here, for the first time the technique of frequency resolved optical gating (FROG)has been used to record a second harmonic spectrogram of the VECSEL pulse train,from which the phase information of non-transform limited sub-picosecond pulseshas been retrieved. I also report the characterisation of a single stage VECSEL seededytterbium-doped fibre amplifier, capable of increasing the average power of a VECSELfrom 20 mW to over 1.5 W while maintaining the sub-picosecond duration ofthe pulse train. The amplifier is capable of operating at any repetition rate obtainablewith a VECSEL, amplification is demonstrated here with 1 GHz and 6 GHz seeds.Finally, the nonlinear evolution of VECSEL pulses inside a single stage fibre amplifierhas been investigated. Computer modelling of the linear gain and nonlinearpulse propagation within a single fibre has been used to design an amplifier capableof producing pulses with a parabolic profile. The modelling reveals that a parabolicamplifier would produce spectrally broader linearly chirped pulses which could becompressed to below 100 fs, with average powers 3 W. An experimental realisationof the parabolic amplifier will require a seed with average power greater than100 mW, this could be achieved with a re-growth of an existing sample, QT1544.
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