Engineered optical materials by ultrafast laser nanostructuring

Abstract

This thesis is focused on ultrafast laser induced modification in optical materials including transparent dielectrics, high-index semiconductors, and glass-metal nanocomposites. Under certain conditions, ultrafast laser direct writing through a nonlinear light-matter interaction enables a high-precision nanostructuring. This type of the modification exhibits form birefringence and/or dichroism enabling the fabrication of polarization sensitive optical elements. The main activities involved in the research are the optimization of light-mater interaction processes, engineering the optical properties of materials, design and fabrication of optical elements, and implementation of engineered optics into the multidisciplinary fields. The pioneering steps were taken towards a practical exploitation of femtosecond laser imprinted space-variant optical elements and development of a novel scheme for optical trapping. As a result, a set of novel optical components with high efficiency, high phase density and low losses were successfully developed and demonstrated, including optical dichroic elements, polarization gratings, arrays of polarization micro-lenses and micro converters, and computer generated Fourier holograms. A novel type of optical tweezers with tunable orbital angular momentum was also designed and developed, which has attracted attention from the beam-shaping and optical micro-manipulation communities. The record high topological charge torque with high-precision control of trapped micron-size objects was achieved. Practical laser imprinted optical elements in materials other than fused silica were demonstrated. A number of optical elements were realized in amorphous silicon thin-films. It was demonstrated that the laser-induced periodic thin-film structures exhibit giant birefringence and was implemented in space-variant polarization and phase manipulations. Surface texturing with 30 nm resolution was demonstrated by potassium hydroxide wet etching and ultrafast laser nanostructuring of silica, leading to the fabrication of dichroic glass-metal patterns. Other laser material processing approaches such as single and double pulse irradiation of crystalline silicon, or irradiation of optical materials with tightly focused cylindrical vector beams were implemented. The femtosecond laser shaping of silver nanoparticles embedded in soda-lime glass was studied. The developed approach can be employed to control the anisotropy of the glass-metal nanocomposites.

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