Sapphire is a substrate in many applications; for example, in watch covers, phone displays, integrated circuits, optoelectronics and light emitting diodes (LEDs). To be useful for these applications, sapphire boules have to be separated into wafers and chips for further processing. This thesis investigates an important processing step of sapphire, namely the laser singulation of sapphire.Previous studies showed that the surface morphology of patterned sapphire substrates (PSS) enhanced the light emission of LEDs. However, the effects of surface morphology on the optical properties of sapphire during laser scanning have not been properly studied.This thesis examined the interaction between the laser beam and sapphire of different surface roughness. Experiments conducted confirmed the proposed hypothesis in this investigation that a sample with a single rough surface exhibited higher levels of absorbance compared to a sample with two polished surfaces. This is predominantly a result of internal reflection at the exit surface.As such, internal reflection can be enhanced by orientating the sample such that the rough surface was facing away from the laser beam source. The presence of the rough surface encourages nonlinear absorption within the sample at lower incoming laser intensities. Significantly more nonlinear absorption could be observed in the sample with its rough surface facing away from the laser, i.e. with a bottom rough surface. As a result, ablation scribes were observed on both top and bottom surfaces of a sample after picosecond laser irradiation at 1.7 W with a focused spot diameter of 27.1 m on the top surface of the sample. Therefore, the presence of the bottom rough surface improves the nonlinear interaction between the laser beam and the sample.xiii Symbol Unit Description Θ Degree (°) Divergence half angle Degree (°) Angle of light with respect to normal Degree (°) Critical angle Degree (°) Angle of incident light Degree (°) Angle of refracted light, unless otherwise stated 1 Degree (°) Angle made on entry surface, unless otherwise stated 2 Degree (°)