Parallel diffractive multi-beam ultrafast laser micro-processing

During the last decade, ultrashort pulse lasers have been employed for high precision surface micro-structuring of materials such as metals, semiconductors and dielectrics with little thermal damage. Due to the ultra high intensity of focussed femtosecond pulses (I > 1012W/cm2), nonlinear absorption can be induced at the focus leading to highly localised material ablation or modification. This is now opening up applications ranging from integrated optics, through multi-photon induced refractive index engineering to precision surface modification for silicon scribing and solar cell fabrication. To ensure non thermal material processing, the input fluence (F) of the ultrashort pulse laser must be kept in the low regime (F ∼ 1Jcm-2), a few times above the well defined ablation threshold. Accordingly, μJ (10-6J) level pulse energy input is often required for ultrashort pulse laser fine micro/nano-surface structuring. Running at one kilohertz repetition rate, many current ultrashort pulse laser systems can provide mJ (10-3J) level output pulse energy. Accordingly, significant attenuation of the laser output is required for many applications and hence causes a great deal of energy loss. With this limitation in mind, holographic multiple beam ultrashort pulse laser processing, where the mJ pulse energy is split into many desired diffracted beams with arbitrary geometric arrangement, is proposed in this thesis. The multi-beam patterns are generated by phase modulation using computer generated holograms (CGHs) which are displayed on a Spatial Light Modulator (SLM). The ability to address these devices in real time and synchronize with scanning methods adds an additional flexibility to the processing. The results obtained in this thesis demonstrate high precision micro-fabrication of different kinds of materials with greatly increased processing efficiency and throughput, showing many potential industrial applications.EThOS - Electronic Theses Online ServiceGBUnited Kingdo