Fabrication of thz difractive optical elements using direct laser ablation

During the past three decades the growth of interest in THz electromagnetic wave band was enormous. Despite that, the development of mirrors, modulators, waveguides, antennas, lenses and other devices for THz band is still not complete and needs much more investigation. Monocrystalline silicon is partially transparent material for THz waves and can, therefore, be used to produce various components. A promising alternative to traditional monocrystalline silicon machining methods (used for fabrication of components for THz wave band) is direct laser ablation. The use of direct laser ablation for silicon fabrication enables the formation of structures with micrometer precision that is more than enough for THz applications. The first part of this thesis introduces reader to: essential theory that is needed to understand the processes taking place during the laser processing of silicon wafers, classification of the fabricated components and detailed description of equipment used in the experiments. Second part of this paper is about performed experiments which can be divided to three subparts. First subpart consists of experiments dedicated to determine system parameters for the most efficient laser ablation of silicon and comparing pros and cons of nanosecond and picosecond laser processing. Second subpart of this work was the fabrication of focusing elements for THz band using experimentally obtained optimal parameters for monocrystalline silicon laser ablation. Last subpart of this thesis was made cooperating with FTMC Terahertz photonics laboratory in measuring focusing characteristics of fabricated elements for THz wave band. Investigation of fabricated THz optical elements verified that all correctly fabricated elements demonstrated characteristics highly correlated with theoretical predictions. 1/8 period PZP lenses, proved to be the best option for THz band focusing. Integration with antireflection structures demonstrated even further increase of THz focusing element efficiency