Higher-Order Poincar e Beams from Lasers
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Date
2019
Authors
Sroor, Hend
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Abstract
Traditional laser systems are usually designed in such a way as to produce the fundamental
Gaussian mode. The Gaussian mode, however, is not ideally suitable for all
applications at hand, thus presenting the need for structured light modes. These modes
have captured great attention due to their unique properties and have found a myriad
of applications.
Laser modes are often characterised based on intensity measurements to infer, through
propagation, the beam quality factor. This detection scheme does not consider the
polarisation state of the laser mode. Therefore, it is only e ective for measuring the
quality of laser modes with uniform polarisation (scalar modes). Structured modes with
non-uniform polarisation, namely vector beams, are usually di erentiated from scalar
beams by qualitative measures, for example, visual inspection of beam pro les after a
rotating polariser. There is no quantitative measure de nes the quality of a vector mode,
i.e. a measure that can tell how vector the beams is. Consequently, there are still many
open questions such as: how can we manipulate light's degrees of freedom inside the
resonator to control the generation of di erent families of structured light? And how
can we detect and characterise these modes?
The work presented in this thesis subsequently focuses on laser beam shaping inside
solid state resonators. Here we will generate desirable transverse modes of structured
light and develop tools to detect them. We consider two approaches for laser beam
shaping inside the laser resonator. The rst approach involves using amplitude masking
inside unstable canonical resonators to allow controlled generation of a unique family
of structured modes known as fractal modes. The second approach involves coupling
of light within metasurefaces inside the resonator for the selection of pure higher-order
Laguerre-Gaussian modes and superpositions thereof. Subsequent to this, we develop a
novel technique to quantitatively identify the purity of structured modes based on their
\vectorial" nature. Finally, we investigate how the properties of such beams change
when they are ampli ed through birefringent and isotropic amplifiers.
Description
A thesis submitted in ful lment of the requirements
for the degree of Doctor of Philosophy in Science
in the School of Physics
February 2019
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Citation
Sroor, Hend Mohammed. (2019). High-order Poincaré beams from lasers. University of the Witwatersrand, https://hdl.handle.net/10539/28804