This thesis discusses the development of time resolved fluorescence imaging techniques and their use in the study of cellular signalling pathways, in particular the ability to perform multiplexed imaging of a number of pathways in live cells. These techniques are applied to investigate chemotaxis, the ability of cells to migrate directionally in response to a chemoattractant gradient, which requires precise spatiotemporal coordination of signalling events. Fluorescence lifetime imaging (FLIM) is widely applied to obtain quantitative information from fluorescence signals, particularly using Förster Resonant Energy Transfer (FRET) biosensors to map protein-protein interactions in live cells. The development of a software tool for the global analysis of large FLIM datasets is presented which allows simultaneous analysis of hundreds of FLIM images in minutes and the use of complex models, for example a four-exponential model of an ECFP FRET system, with relatively low photon-count data. Live cell imaging with optimised FRET biosensors is used to investigate the role of Phospholipase C epsilon (PLCε) in fibroblast chemotaxis. It is demonstrated that PLCε-null fibroblasts show a compromised chemotactic response to platelet derived growth factor and spatial defects in Rac1 activation and phosphoinositide signalling. The ability to image multiple functional reporters simultaneously in a single cell is desirable when investigating complex signalling networks with significant cross-talk such as chemotaxis. A number of approaches for multiplexed measurements are investigated, in particular using homo-FRET between two spectrally identical fluorophores, which presents a promising approach to reduce the spectral bandwidth compared to conventional hetero-FRET biosensors. The optimisation and automation of a to perform multiplexed time-resolved fluorescence anisotropy imaging of homo-FRET biosensors is discussed. The development and multiplexed imaging of homo-FRET reporters for phosphoinositide signalling using a polarisation resolved confocal time correlated single photon counting (TCSPC) microscope is presented. Potential approaches for multiplexed imaging three functional reporters are discussed.

The first part of this thesis is devoted to the synthesis, purification and application of a series of indenopyrazine based polymers for their use in optoelectronic devices. The work focuses on the effect of alternating chain length on the degree of polymerisation, optical and charge carrier properties The next section studies the copolymerisation of indenopyrazine with dithiophene benzothiadiazole acceptor units and the effect substituents have on the planarity of the polymer backbone and the delocalisation of molecular orbitals and solar cell performance. The final part of this thesis investigates indenopyrazine based polymers as charge carrier materials in p-type transistors and probes the effect p-dopants have on the energy levels, charge carrier mobility and optical properties. The second part is the synthesis of the novel alkylidene-indenopyrazine monomer and probes the introduction of enforced planarity and finally the synthesis towards the novel the semiconductor indenopyrazinedithiophene.

In this thesis the quantum theory of light in absorbing media, macroscopic quantum electrodynamics, is extended to describe the quantised electromagnetic field in general linear absorbing media. The Casimir-Polder potential between a particle and examples of bianisotropic media are presented. The electromagnetic properties of a general linear medium that may possess a spatially non-local and even non-reciprocal response are fully described by a complex conductivity tensor. The quantisation of the electromagnetic field in general media was achieved through enforcing a commutation relation between Langevin noise current operators whose presence also ensure compliance with the fluctuation dissipation theorem. The quantisation of the electromagnetic field in media characterised by bianisotropic response functions is shown. The duality invariance of an electromagnetic system was found to be a continuous symmetry in general and a discrete symmetry when the medium has a reciprocal response. The chiral component of the Casimir-Polder potential was derived in the weak coupling regime. It was found to be either attractive or to repel chiral molecules, depending on the chiral identity of the objects. The molecule and the medium must both possess chiral features otherwise the chiral contribution to the Casimir-Polder potential does not exist. By constructing a cavity between media of opposite chirality, enantiomer separation can occur when particles are initially in an excited state and the resonant frequency of the media is equal to the relevant transition frequency of the molecule. The quantisation of the electromagnetic field in moving media was achieved on the observation that a locally responding isotropic dielectric in motion is equivalent to a non-reciprocal linear bianisotropic medium from the perspective of a moving frame. A generalised reciprocity condition that constrains the Green's function of the electromagnetic field in moving media was derived.

In this thesis we investigate the response of plasmonic systems in a quantum optics setting. This work can be grouped into two sub-investigations, the study of macroscopic and microscopic responses. The narrative of the thesis comprises three principal parts. First, we give an in-depth review of the field of quantum plasmonics as it is an important theme that runs through the work contained in this thesis. In particular, we focus on outlining the cutting edge research that is being done on the intense interactions between plasmonic systems and quantum emitters. This leads naturally to the first investigation into the macroscopic response of quantum plasmonic systems in a metamaterial setting. We outline how complex hybrid systems of plasmonic metal nanoparticles (MNP) and two-level quantum dots (QD) can be used to create a quantum plasmonic metamaterial. Metamaterials are structures composed of periodic lattices of identical subwavelength unit cell scatterers, each of which governs completely the electromagnetic properties of the entire bulk material. We theorize the use of MNP-QD nanorings as a unit cell in order to control the macroscopic magnetic properties of the metamaterial. We outline how such a metamaterial can have a tunable, and saturable, magnetic permeability. In the last part of the thesis we consider the model of a single light mode interacting ultrastrongly with a collection of emitters, in the anticipation that quantum plasmonic systems can be brought into this ultrastrong-coupling regime (USC). In particular we study the emission of the system after the coupling between the light mode and the emitters is non-adiabatically switched-on. We find evidence that for both two-level, and multi-level, emitters in the USC, both the counter-rotating terms and the diamagnetic term must be included to prevent qualitative errors.

Cavity polaritons are quasiparticles formed when a photon con ned within a cavity interacts with an elementary excitation in a semiconductor that is called exciton. Under the right conditions, cavity polaritons form a macroscopic condensate in the ground state. This condensate decays through the cavity mirrors, thus providing coherent light-emission: a phenomenon termed polariton lasing. The threshold for polariton lasing can be signi cantly lower than that required for conventional lasing. Large exciton binding energies are an essential requirement to obtain polariton lasing at room temperature. Group III nitrides and ZnO are the only inorganic semiconductors possessing Wannier-Mott exciton binding energies above 25 meV, the room-temperature thermal energy. In contrast, Frenkel excitons in organic semiconductors possess binding energies of 1 eV and are thus highly stable at room temperature. This thesis consists of two parts. The first part concerns the fabrication and optical characterisation of samples consisting of an ultra-smooth GaN membrane encapsulated in an all-dielectric (SiO2/Ta2O5) distributed Bragg reflector (DBR) microcavity. By utilising the selective photo-electro-chemical (PEC) etching of an InGaN sacri cial layer, GaN membranes 200 nm thick are produced and introduced between DBRs. The second part is devoted to the demonstration of a room-temperature organic polariton condensate. The studied samples consist of a thermally evaporated 2,7-bis[9,9-di(4-methylphenyl)-fluoren-2-yl]-9,9-di(4-methylphenyl) fluorene (TDAF) thin film enclosed within an all-dielectric microcavity, consisting of SiO2 and Ta2O5 pairs. In both GaN and organic systems, the strong coupling for various detunings is demonstrated by performing angle-resolved reflectivity and photoluminescence (PL) measurements. On reaching threshold, the nonlinear increase in the PL is blueshifted with respect to low power emission, and is accompanied by a simultaneous reduction in the linewidth, marking the onset of polariton lasing at room-temperature. In the organic microcavities particularly, the condensate formed above threshold is linearly polarised and exhibits o -diagonal long-range order with a spatial coherence that is dependent on the pump shape. Moreover, the ambipolar electrical characteristics of this organic semiconductor and the high electron mobility of GaN suggest both materials as promising candidates for direct electrical injection.

When brown dwarfs were first discovered two decades ago, they were introduced as the missing link between stars and giant planets. This led to the extension of the stellar classification sequence down to the planetary regime by introducing the spectral types L,T and Y. We are now in the era of brown dwarf science where large homogeneous samples can be produced, allowing us to learn about their physical properties in a statistically meaningful way. In this thesis we present a new method, dubbed photo-type, which makes the classification of L0-T8 dwarfs significantly faster as it only relies on already available multi-wavelength photometry. It is based on X2 template fitting and can be adapted to use on any photometric data. photo-type classifies L and T dwarfs to an accuracy better than 1 spectral type, making it comparable to spectroscopy. This is tested by a range of different methods, ranging from simulations to spectroscopic follow up. By searching the SDSS+UKIDSS+WISE for L and T dwarfs with 13.0 < J < 17.5 we produce the largest homogeneous sample of these dwarfs to date. These 1157 L and T dwarfs are used to find peculiar objects and populations (e.g. blue/red outliers), L/T binaries, and benchmark systems (by crossmatching with a proper motion catalogue). It also allows us to calculate the best estimates of the space densities of L and T dwarfs to date. By following up several of the peculiar ultra cool dwarfs in our sample, we found a very young object (10Myrs), a number of dusty sources, and some that remain unexplained. Finally, we conducted a general search for rare objects in UKIDSS. Here we were interested in finding high redshift quasars, very cold white dwarfs or a yet unknown population by analysing objects with large X2 values. While none of the above were found, we did find a moderate temperature H and He atmosphere white dwarf, a carbon star and some medium redshift quasars.

Negative refraction and sub-wavelength resolution have been demonstrated with metamaterials throughout the past decade. This thesis introduces a quantum metamaterial, based on quantum mechanical principles, which exhibits negative refraction and sub-wavelength resolution with reduced absorption compared to non-quantum metamaterials. In particular, this thesis introduces a novel method of achieving sub-wavelength resolution using the quantum metamaterial. This method of superresolution does not require a negative permittivity or permeability, as the predecessors require, but is instead based on a dispersion curve with a high elliptical eccentricity. This thesis uses an effective medium approach to calculate the quantum metamaterial's permittivity, which is then used to model super-resolution and negative refraction. After considerable design, optimisation and epitaxial growths, a GaAs based quantum metamaterial is fabricated into a superlens. A scanning near-field optical microscope is used to measure the sub-wavelength imaging capability of the quantum metamaterial superlens.

This thesis presents the development of solution-processable hole-transporting inorganic semiconductors for electronic applications. As the improvement of electron-transporting oxides, such as ZnO, In2O3, and SnO2, has continued to advance, the progress on the hole-transporting counterparts is still largely lagging behind. Copper(I) oxide (Cu2O) is one of a handful oxide materials that shows hole transport. This thesis shows the first demonstration of p-channel TFTs from Cu2O thin films processed from the spray pyrolysis technique. The field-effect hole mobility (μ_FE) is in the range of 10^-4 to 10^-3 cm^2/(V.s) while the on-to-off channel current ratio (I_D^on-off) is on the order of 10^3. The work presented here emphasises the versatility of the spray pyrolysis, which has previously been employed to successfully produce n-type oxides and dielectrics. Another copper(I)-based inorganic compound, copper(I) thiocyanate (CuSCN), has a unique combination of good hole-transporting characteristics and excellent optical transparency. This thesis presents extensive characterisation results of CuSCN thin films from their chemical, electronic, optical, morphological, to structural properties and demonstrates, for the first time, p-channel TFTs with a truly transparent active layer based on a solution-processed wide-band-gap inorganic semiconductor. μ_FE in the range of 0.01-0.1 cm^2/(V.s) has been achieved whereas I_D^on-off is on the order of 10^4. A p-channel unipolar voltage inverter has also been constructed from CuSCN TFTs, showing the possibility of realising transparent electronics. CuSCN-based TFTs are also studied in more details by analysing their transfer characteristics for the distribution of localised states and examining their temperature dependence for the hole transport modes. Furthermore, due to its novel electronic and optical properties, CuSCN is also offered as a replacement of PEDOT:PSS as a hole-transporting layer in bulk-heterojunction organic photovoltaics (OPVs) and organic light-emitting diodes (OLEDs). Owing to its superior optical transparency, CuSCN-based solar cells consistently exhibit higher power conversion efficiency (PCE) than PEDOT:PSS-based cells, especially in the case of cells employing active layers that absorb light in the near-infrared spectral range. Specifically, cells based on PDPP-2T-TT:PC71BM show PCE of ~8% with CuSCN HTL compared to ~6.2% with PEDOT:PSS HTL. In addition, the energy levels of CuSCN lead to a lower hole injection barrier as well as effective electron blocking property, yielding OLEDs with a low turn-on voltage and low leakage current. OLEDs employing an active layer of (PPy)2Ir(acac) in 26DCzPy:TCTA with CuSCN HTL show higher values of highest achievable efficacies (51 cd/A and 55 lm/W at 1 cd/m^2) compared to those with PEDOT:PSS HTL (38 cd/A at 2142 cd/m^2 and 14 lm/W at 1710 cd/m^2).

In this thesis, I describe the development of a high repetition rate femtosecond fibre based chirped pulse amplification system (FCPA) for strong-field physics experiments. This project was set in a newly established sub-group of the Laser Consortium at Imperial College London with the aim to push the strong-field and attosecond science experiments to be conducted at 100s of kHz repetition rate. It was important to design and implement a compact, CEP stable, high repetition rate fibre CPA system. Custom optics and mounts were employed in order to achieve a compact stretcher and compressor design. The stretcher was designed to stretch the oscillator pulses with a bandwidth of 14nm and a duration of 90 fs to 1 ns to avoid non-linearities in the fibre amplifier. It is based on an Offner type configuration. The fast rise time RTP based Pockels cell can be adjusted to deliver 50 -350 kHz of repetition rate to the large mode area (LMA) ytterbium doped fibre with 30 um core and 250 um cladding (Yb1200-30/250DC-PM, Nlight). It was possible to generate up to 13 uJ of pulse energy at 100 kHz repetition rate before compression with 14W pump power. Higher pulse energies up to 130 uJ have been demonstrated at 38W of pumping (55W pump diode Nlight), however mechanical instabilities impaired the spectral and spatial performance at this power level. Improvements to optimise the performance of the system are suggested in the conclusion. Additionally to this experiments in the near-IR have been conducted on post compression mechanisms. The principle of filamentation was employed to generate tunable few-cycle pulses at wavelengths from 1.6 - 2 um and subsequent high harmonic generation in a proof of principle experiment. These results were published in Applied Physics Letters [1] and Journal of Physics B: At. Mol. Opt. Phys. [2].

The T2K (Tokai to Kamioka) experiment uses an intense off-axis muon neutrino beam to study neutrino oscillations through muon neutrino disappearance and electron neutrino appearance. As T2K and other neutrino oscillation experiments move beyond the regime in which they are statistically limited, uncertainties on neutrino-nucleus cross-sections have become increasingly significant as a limiting factor on the precision of these experiments, and on the next generation of detectors. Reducing these uncertainties requires a better understanding of neutrino-nucleus interactions through empirical study. This thesis describes the first ever measurement of neutrino-nucleus interactions on a gaseous target, using the intense T2K beam and the three gaseous argon time-projection chambers in the T2K near detector, ND280. I identify 63 neutrino interaction candidates, and make a comparison of the charged-current muon neutrino differential cross-section with respect to proton multiplicity between data and the simulation packages NEUT and GENIE. This thesis also describes the methods developed to select the gas interactions data sample, which by virtue of the detailed reconstruction available in the ND280 TPCs offers further opportunities to test the predictions of nuclear models than those that are covered by this thesis. Future generations of this analysis are expected to expand both the size of the sample and the range of variables tested.