Abstract
Despite the tremendous advances witnessed in light microscopy over the past two decades, non-invasive optical imaging is still limited to penetration depths smaller than 1 mm into tissue. Multiple scattering caused by the refractive index inhomogeneities of biological matter rapidly distort any optical wavefront prop-agating through, rendering tissues opaque. Such turbidity restricts imaging, as well as other biophotonics techniques, to the most superficial layers of tissue.A perspective strategy to overcome the turbidity of living matter exploits holographic light control in multimode optical fibres. This allows devising min-imally invasive imaging probes with footprints far bellow those of conventional endoscopes, as well as enhanced spatial resolution up to the diffraction limit de-termined by the numerical aperture (NA) of the fibre.
In this Thesis, high-resolution focussing is demonstrated with unprecedented ability across novel specialty fibres offering very-high NAs, by devising a system and methodologies which allow counteracting the severe mode-dependent loss affecting such fibres. The high quality and NA of the generated foci is capable of 3D optical confinement of dielectric microparticles, thus enabling the deliv-ery of holographic optical tweezers introduced through a bare optical fibre with cross-section comparable to a single cell. The holographic methods developed allow the manipulation of complex 3D arrangements of particles, as well as their independent positioning with nanometre-scale precision in all three dimensions.
Separately, a multimode fibre based deep-brain fluorescence imaging is demonstrated in animal models in vivo, allowing the identification of neuronal structures at depths exceeding 2 mm and resolving fine details down to ≈1 µm resolution.
| Date of Award | 2018 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Alfred Cuschieri (Supervisor) & Tomas Cizmar (Supervisor) |