This thesis covers the construction and development of fibre laser Master Oscillator Power Amplifier (MOPA) systems for photoacoustic imaging applications. An initial system developed for photoacoustic tomography was built, based around the use of an Amplifier Spontaneous Emission (ASE) source, modulated by both an acousto-optical modulator (AOM) and an electro-optical modulator (EOM). The system relied on the use of an in-house custom fibre, which allowed the system to generate nanosecond pulses of 9.7mJ energy at 1064nm. This system was then developed to become a more portable system by removing the need for modulators by using a Superluminescent diode (SLED) as a seed source. Despite the size reduction of the system, it was still capable of a 5mJ output. A new system focused on optical resolution photoacoustic microscopy (OR-PAM) was then built. The drawbacks and merits of three different seed sources, a Fabry-perot diode, an ASE source and a distributed feedback (DFB) diode were investigated, indicating that for narrow line width amplification the DFB was best suited. Finally second harmonic generation was tested using the OR-PAM system. We successfully generated over 1μJ of the second harmonic in 3-20ns pulses at repetition rates between 100kHz and 1MHz. The system was then integrated with UCL system to image biological tissue.