Polarization engineering with ultrafast laser writing in transparent media

Abstract

In this thesis novel developments in the field of femtosecond laser material processing are reported. Thanks to the unique properties of light-matter interaction on ultrashort time scales, this direct writing technique allowed the observation of unique phenomena in transparent media and the engineering of novel polarization devices.

Using tightly focused femtosecond laser pulses’, high average power second harmonic light was generated in the air with two orders of magnitude higher normalised efficiency than reported by earlier studies. We also demonstrated optical vortex generation in the air as a result of spin-orbital momentum coupling in the frequency doubling process.

The ultrashort laser pulses were also explored as a tool for micro-bubble formation. Due to the high refractive index contrast at the interface of a bubble and the glass substrate we observed edge birefringence, which could be utilised for optical vortex generation or as a radial polarizer. The experimental observation was supported by a theoretical model.

Finally, a series of birefringent optical elements were developed based on self-assembled nanostructures induced by ultrashort laser pulses in fused silica. The process was discovered a decade ago and mostly was regarded as a scientific curiosity. However, we demonstrated that these nanostructures can be used as the building blocks for novel optical elements based on spatially varying birefringent properties.

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