Plasmonic nanoparticles can act as ultrafast nanoheaters that can be employed in a wide variety of environments. The light absorbed by these nanoparticles is converted into heat in picoseconds, which in turn heats the surroundings of the nanoparticles. As the resulting heating is localized both in time and in space, it is challenging to study directly. One technique that can resolve this heating in time, is transient absorbance (TA) spectroscopy. When using core–shell nanoparticles with a gold core and a silica shell, effects other than heating such as hot electron injection are prevented. In this work, the potential of gold–silica core–shell nanoparticles as ultrafast nanoheaters is explored. The different chapters explore the synthesis of these nanoparticles and how their heating affects their environment, both theoretically and experimentally through TA spectroscopy. ... Read more

eXtended reality (XR) has become a core instrument for studying pedestrian behaviour, yet the field remains fragmented: researchers build single-use, VR-only simulators that lack cross-modal transferability, behavioural data collection pipelines, and validation instruments. This paper presents the design and development of the XR Design Toolbox for Pedestrian Behaviour Studies, a modular Unity-based framework that unifies experiment design across virtual reality (VR), augmented reality (AR), and mixed reality (MR). Built as a design artefact, the toolbox comprises six interoperable modules enabling in-situ scene authoring, spatial registration for cross-modal coordinate alignment, standardised behavioural data channels, and in-headset subjective questionnaires. A within-subject fire evacuation case study with 162 XR sessions across VR, AR, and MR on Meta Quest 3 and Magic Leap 2 confirmed that the toolbox maintains spatial and procedural fidelity across modalities. The toolbox shifts the researcher's workflow from ad-hoc simulator development to systematic, cross-modal experimental design, directly addressing the reproducibility and standardisation problems in pedestrian behaviour and urbanism research. ... Read more

Ultrafast photoacoustic metrology offers a potential route for detecting alignment structures buried beneath optically opaque layers in semiconductor wafers. Interpreting the measured transient reflectivity is challenging, however, because the signal results from the coupled processes of optical absorption, electron–phonon energy transfer, thermoelastic generation, acoustic propagation, interface interactions, and optical detection. This thesis develops a physics-based framework for analysing these processes in an aluminium-coated silicon structure.

The measured response is decomposed in the frequency domain as Y(ω) = D(ω)H(ω)S(ω), where S(ω) represents thermoelastic source formation, H(ω) the structural and acoustic response, and D(ω) the optical detection sensitivity. Analytical models are combined with experimental transient-reflectivity measurements and a COMSOL Multiphysics model. A semi-infinite thermal-diffusion model is used to describe the slow thermal background and infer the Al–Si thermal interface conductance. The model reproduces the ideal-interface limit of the numerical simulation, while fits to two experimental datasets yield conductances of approximately 177 and 195 MW m⁻² K⁻¹, with a mean of 185.9 MW m⁻² K⁻¹.

The framework is subsequently applied to investigate prominent spectral components observed near 40 and 120 GHz. The high-frequency response cannot be explained by the aluminium-film eigenfrequencies alone. The optical absorption depth produces substantial source content near 110 GHz, while finite electron–phonon equilibration reduces and shifts this content. The Al–Si interface further modifies the resonance frequencies and amplitudes through its frequency-dependent reflection phase and magnitude. Optical detection introduces additional frequency-dependent weighting through the spatial overlap between the strain field and the probe sensitivity.

The combined model qualitatively reproduces the principal spectral features. An effective frequency-dependent attenuation law fitted to successive measured echoes is included in the analytical and COMSOL models, giving good agreement with the observed echo decay. This agreement supports the implementation, while independent validation of the attenuation law remains future work.

The results show that increasing acoustic frequency and maximizing detectable echo amplitude are competing design objectives. Effective system design must therefore jointly consider optical absorption, electron–phonon coupling, structural resonance, interface transmission, propagation losses, and optical sensitivity. ... Read more

Rising global demand for agricultural produce and increasing labor shortages have accelerated interest in robotic automation for harvesting tasks. Delicate mushroom grasping remains particularly challenging because maintaining a stable grasp without damaging the mushroom requires both normal and tangential contact information.

Vision-based tactile sensors that combine normal and tangential sensing provide rich tactile information for delicate robotic grasping. However, current high-resolution designs are often too bulky for the confined workspace of mushroom harvesting. Although compact vision-based tactile sensors have been proposed, they often sacrifice sensing capability to achieve smaller dimensions. This thesis therefore investigates how a compact vision-based tactile sensor can retain both normal and tangential sensing capabilities while satisfying the geometric constraints of robotic mushroom grasping.

To address this challenge, this thesis proposes a compact vision-based tactile sensor for delicate robotic mushroom grasping. A folded mirror-based optical path, RGB illumination, and embedded dimples were combined within a compact sensor architecture to capture both normal and tangential deformation while reducing fingertip thickness. In addition to the developed prototype, this work identifies the geometric, optical, and illumination design requirements for implementing reliable shadow-based tactile sensing in compact vision-based tactile sensors.

The resulting sensor achieved a tip thickness of 9.13 mm and a center thickness of 12.9 mm. The center thickness represents a 66% reduction compared with the original ShadowTac geometry. For the evaluated mushroom configuration, geometric accessibility increased from 45% to 81%. Mushroom sliding experiments demonstrated that the resulting tactile images supported deformation tracking. The captured deformation patterns enabled a Multi-Layer Perceptron (MLP) to predict the evolution of the grasp safety margin with a mean absolute error (MAE) of 0.051, root mean squared error (RMSE) of 0.068, and a coefficient of determination (R²) of 0.952. The prediction accuracy decreased near gross slip, where low safety margins were generally overestimated. However, these results demonstrate the feasibility of combining compact sensor geometry with tactile sensing relevant to robotic mushroom grasping. ... Read more