Investigation of selective laser-induced etching in the volume of sapphire

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Ultrashort pulsed laser radiation (t = 500 fs) is focused into the volume of sapphire. By nonlinear absorption processes like tunneling and multi-photon absorption in the focal volume of the laser radiation energy is deposited into the solid. Due to electronic and thermal processes a change in the material structure and thus a change of the material density and the refractive index are caused. Modifications induced by femtosecond laser radiation are selectively wet etchable, whereas the unmodified material remains almost unaffected. With this writing technique and the subsequent etching process it is thinkable that even complex hollow structures are produced in the volume of transparent materials.In this project the fundamental understanding of the process will be developed for in-volume selective laser-induced etching (ISLE) of sapphire by systematically varying the process parameters. Therefore a subsequent process development of three-dimensional structures shall be realizable based on the identified process window and a quantifiable prediction of the etching process. On the one hand, the effect of process parameters on the crystalline structure (amorphization e.g.) and on the other hand, the influence on the etchability of sapphire by laser-induced modifications are studied. A quantifiable correlation between the used process parameters and the etchability, such as an induced deformation of the focal volume due to spherical aberrations during focusing, the formation of periodic nanostructures and the occurrence of heat accumulation effects shall be determined experimentally. Furthermore, the influence of the already modified material and thus the induced refractive index modifications on the subsequent laser pulses is investigated in order to describe the influence of the already modified material on the focal geometry and the absorption behavior of the laser radiation. In this project a holistic approach is selected to enable a subsequent precise process development for three-dimensional structures in the volume of sapphire by laser-induced etching.