Quantum technology has revolutionised academia and industry by potentially solving many
problems that are not feasible and accessible for conventional technology. Quantum materials like colour centres in diamonds are a promising quantum technology platform in research
and industry. Herein, the development of the room-temperature diamond maser as a quantum
device for oscillators and low noise amplifiers is presented. This thesis investigates both experimental and analytical research in characterising diamonds, mainly Nitrogen-Vacancy (NV)
centres, for masing and maser devices, as well as theoretical and simulation work in designing masers and threshold conditions. Besides the research specifically into the maser, optical
characterisation of these quantum materials is conducted. This thesis primarily focuses on the
maser, but the defect centres characterised have wider use in quantum technology. To push
forward the analytical methods for diamond optical characterisation, this thesis employs multiple algorithms in fluorescence lifetime imaging that improve the performance of conventional
methods. Furthermore, a hybrid quantum algorithm is employed to aid the analysis of optical
data, which utilises unconventional quantum properties of quantum circuits and simulators to
analyse quantum materials for developing quantum devices.