Mode-locked vertical-external-cavity surface emitting lasers

Foreman, Hannah D (2006) Mode-locked vertical-external-cavity surface emitting lasers. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

Vertical-external-cavity surface-emitting lasers (VECSELs) incorporate a semiconductor-based gain chip within an external cavity to form a unique category of laser. These devices draw upon the advantages of both semiconductor diode lasers; with broad gain bandwidths, spectral flexibility with design, and inexpensive fabrication, and the solid state laser family; with functional versatility provided by the external cavity, high power operation enabled by optical pumping, and high beam quality even at high powers. Following the important achievement of mode-locking of using a semiconductor saturable-absorber mirror (SESAM), this thesis is an experimental investigation of the further development and application of VECSELs emitting at wavelengths around 1 μm.

In the work presented here, the fabrication of VECSEL chips to optimise their performance is investigated: satellite pulses in the autocorrelation of a ML-VECSEL pulse are eliminated through back-surface polishing of gain and SESAM chips and thermal management of VECSELs is investigated, concentrating on 2 key approaches; intracavity heatspreader windows, and substrate removal. A ML-VECSEL is used to seed for a high power master-oscillator power amplifier. The seed pulses are amplified to an average power of 184 W with 77% efficiency. Peak powers of 28 kW are demonstrated, and pulse compression to 291 fs is achieved. Finally, development of a micro-imprint lithography method for the realisation of high repetition-rate (>100 GHz) operation of ML-VECSELs is presented. Focusing structures fabricated in GaAs are demonstrated, successfully overgrown and characterised.

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