Femtosecond pulse generation in surface-emitting semiconductor lasers

Abstract

In this thesis I report significant advances towards the goal of stable ultrashort pulse generation in mode-locked optically pumped vertical external-cavity surface-emitting lasers (VECSELs). Continuous wave VECSELs were first designed as a type of semiconductor laser capable of producing high output power in near transform-limited beams. Optical pumping allows the output power of the device to be increased simply by increasing the pumped area of the sample, and an external cavity forces the laser into single transverse mode operation. VECSELs’ external cavities also allow for the insertion of semiconductor saturable absorber mirrors (SESAMs) for modelocking. Mode-locked VECSELs have surpassed the performance of other types of mode-locked semiconductor laser, with modelocking via the optical Stark effect allowing VECSELs to produce sub-picosecond pulses in transform-limited beams, at power levels up to 100 mW and at GHz repetition rates.
The work presented in this thesis describes recent progress in reducing the durations of VECSEL pulses to below 100 fs. At these pulse durations, gain saturation forces the laser oscillator to enter a dynamic regime never before seen in semiconductor lasers, which is also investigated here. In addition, the timing jitter of a VECSELmode-locked using the optical Stark effect is characterised for the first time, and a versatile frequency-divider-based active stabilisation technique is demonstrated. Finally, the fabrication of carbon nanotube based saturable absorbers for VECSEL modelocking via solution processing is investigated.

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