The bright squeezed vacuum state of light is a macroscopic nonclassical state found at the output of a strongly pumped unseeded travelling-wave optical parametric amplifier. It has been applied to quantum imaging, quantum communication, and phase supersensitivity, to name a few. Bright squeezed states are in general highly multimode, while most applications require a single mode. We separated two nonlinear crystals in the direction of propagation of the pump in order to narrow the angular spectrum down to a nearly-single angular mode. We observed noise reduction in the photon number difference between the two down-converted channels, which constitutes of proof of nonclassicality. By introducing a dispersive medium between the two nonlinear crystals, we were able to tailor the frequency spectrum of bright squeezed vacuum and to dramatically reduce the number of frequency modes down to 1.82 ± 0.02, bringing us closer to truly single-mode bright squeezed vacuum.

New mono-chelate complexes with ferrocenyl (Fc), octamethylferrocenyl (Me8Fc) and diaminophenyl (Dap) donor groups, connected through a conjugated bridge, to ZnCl2, Zn(OAc)2 or ReCl(CO)3 acceptor groups, are described. A thorough characterisation of the complexes is provided, including single crystal structures for one pro-ligand and three complexes. Visible d(FeII)→π* metal-to-ligand charge-transfer (MLCT) bands accompany π→π* intraligand charge-transfer absorptions in the UV region. TD-DFT calculations confirm the nature of these absorptions and indicate transitions at higher energies also contain some d(FeII)→π* character. Fc and Me8Fc containing chromophores display a fully reversible oxidation process when probed electrochemically. Molecular quadratic nonlinear optical (NLO) responses are determined using hyper-Rayleigh scattering (HRS) and Stark spectroscopy. Larger β values are determined for complexes with Dap donors and ReICl(CO)3 acceptors. A family of novel fac-ReI(Lax)(CO)3(N-N) complexes, where N-N is 4,4′-dicyano-2,2′-bipyridyl (dcnbpy) or 4,4′-bis-(p-cyanophenyl)-2,2′-bipyridine (bbnbpy), with various axial ligands (Lax) are reported. The ReI complexes are useful precursors for metalation with electron-rich RuII ammine donor groups, to prepare novel tri-metallic V-shaped molecules. Single crystal X-ray structures are reported for five ReI complexes, confirming the fac geometry of the carbonyl ligands; the ReI complexes also display stretching frequencies typical of fac-ReI(Lax)(CO)3(N-N) complexes. The UV-visible spectra contain a low intensity band due to a d(ReI)→π*(bpy) transition, along with a more intense π→π* band. 1H NMR studies reveal the formation of trimetallic complexes, upon treatment of ReI complexes with a molar excess of [RuII(NH3)5(H2O)][PF6]2.The synthesis of octupolar heptametallic complexes containing RuII ammine donor groups has been investigated. The ligand 4,4′-bis-[(E)-2-(4-cyanophenyl)ethenyl]-2,2′-bipyridine (bbnpe) was used to prepare tris-chelate complexes of various transition metals, in order to understand its complexation behaviour. The ZnII tris-chelate BPh4– salt was treated with a 10 molar excess of a RuII ammine aquo complex, to produce the heptametallic complex as a mixed anion salt. HRS and Stark spectroscopy have been used to determine the quadratic NLO response for the heptametallic mixed anion complex salts, the latter gives large β0 values, approximately 10–27 esu. Density functional theory (DFT) calculations have been carried out on twelve cationic, 2D NLO chromophores with pyrazinylbis(pyridinium) electron acceptors with either 4-(methoxy/dimethylamino)-phenyl or pyridyl coordinated {RuII(NH3)5}2+/trans-{RuII(NH3)4(py)}2+ electron donor groups and the results compared with data previously obtained experimentally. The B3LYP/6-311G(d) level of theory was used to model the absorption spectra and to calculate static hyperpolarisability (β0) values, whilst the B3LYP/LANL2DZ/6-311G(d) level was used for the complexes. The extent of prediction of trends in ICT bands and β0 is partial, with the main discrepancies relating to the progression from one to two electron donor groups. The quantitative accuracy of predictions diminishes as the systems depart from a relatively simple one-dimensional (1D) dipolar motif.

The organic-metal interface is ubiquitous in a wide variety of natural environments and industrial applications. As a result, the interfacial chemistry has been studied for many decades. Specifically, the surfactant-metal interfaces play an important role in the prevention of metallic corrosion where surface active corrosion inhibitors are often used as a prevention method. Development of a spectroscopic method based on vibrational sum frequency generation, specifically for metal interfaces, is carried out with the goal of elucidating the surface structure of these molecules. The contribution to the signalarising from the metal substrate often plays a crucial role in the quantitative analysis of spectra. By adopting a phase-resolved detection scheme, the polar orientation of the organic molecule adsorbed on metal surfaces is experimentally obtained. Furthermore,the development of a novel acquisition scheme is demonstrated where the incident angle is scanned while simultaneously measuring the magnitude and phase of the nonlinear response. This enables the separation of all contributions to the nonlinear susceptibility tensor governing the response. Such an approach is especially useful when the conventional nonlinear vibrational technique is inaccessible in beam polarizations where the infrared field is perpendicular to the plane of incidence, due to the infrared surface selection rule of metals. Finally, this approach is used to examine the structure of a surfactant on iron surfaces. / Graduate / 2022-09-08

Parametric down-conversion (PDC) is a nonlinear optical process widely used to generate pairs of photons. It occurs when an intense laser traverses an optical parametric amplifier (OPA). When the gain of the amplifier is increased, the number of downconverted photons increases exponentially: this is the high-gain regime of PDC. High-gain PDC is potentially a versatile tool for metrology. It is a source of highly-entangled states and bright squeezed states for applications in quantum information and interferometry. In addition, the high number of photons in high-gain PDC makes it possible to use diodes and cameras directly, instead of single-photon detectors and coincidence-counting apparatus. However, all the quantum-optical experimental methods need to be generalized or adapted for a high-photon flux. Most of the theoretical and experimental techniques used or developed in this thesis aim to address this transition from low to high-photon flux of PDC. I theoretically and experimentally provide strategies to harness the mode structure of PDC, bringing us steps closer to a usable source of bright squeezed vacuum for interferometry and quantum imaging. I present experimental progress in reducing the number of frequency modes of high-gain PDC, which is naturally broadband, and consequently highly multimode. Our theory for high-gain PDC generated in a nonlinear crystal provides a set of modes containing physically meaningful information, i.e. the pairwise quantum correlations between independant modes. In addition, I provide a thorough discussion on the limit of SU(1,1) interferometry in regards to internal loss and gain unbalancing. Finally, I tie the frequency spectrum of high-gain PDC to the properties of vacuum fluctuations, allowing to predict the number of photons from first principles, making it a powerful tool for spectroradiometry. Those developments are a springboard towards usable high-gain PDC for metrology.

Self-trapped beams of light propagate while maintaining their initial intensity profile within a self-induced channel of high refractive index. When multiple self-trapped beams or filaments travel within the same medium, a diverse host of interactions are observed, including attraction, repulsion, fusion, annihilation, and birth. This thesis describes studies of interactions between large and small filament populations and/or beam-induced structures (waveguides) within polymer media. The understanding developed in this fundamental work was applied to design polymer cuboids – the cuboids that count – with computing-inspired functionality. First, the spontaneous self-organisation of randomly-seeded waveguides within a photopolymer material formed the basis of 3 operations: (i) data transfer; (ii) volumetric encoding; and (iii) binary arithmetic. The same material was used for 3D data storage using highly-intersecting waveguide lattices. The pursuit of enhanced capacity prompted an exploration of light coupling in waveguides with small angular separation and significant field of view overlap. Using multiple angled light sources, we successfully demonstrated single-step data writing and multiplexed data reading in these structures. Finally, we examined long-range interactions between 2 to 4 collinear beams within a spiropyran-functionalised hydrogel. The mechanism of refractive index increase in this medium – a light-induced volume contraction and expulsion of water – allowed beams to inhibit their neighbours’ self-trapping, with a clear relationship between number of neighbours and degree of inhibition. These observations were used to form the basis for an optical hydrogel NAND gate. / Thesis / Doctor of Philosophy (PhD)

No description available.

Nonlinear optical processes have been used for many years to cause light to behave in unique ways. These can influence various aspects of the light beams, including the spatial intensity profile. More specifically, a naturally divergent beam can maintain its initial beam profile when propagating through a nonlinear medium due to the increased refractive index causing focusing. This process is called self-trapping and can be elicited for both coherent and incoherent light in a number of nonlinear media. Analogous to this, modulation instability (MI) is a nonlinear process that causes a broad beam of light of break up into a large population of self-trapped filaments. When these processes occur in photopolymers, light guiding structures are inscribed within the material and persist even after the light is removed. Our group has previously studied the behaviour and interactions of light undergoing self-trapping and MI in photopolymer systems. The studies presented in this thesis show novel interactions between multiple incoherent beams undergoing MI, utilization of these interactions, as well as the development of new polymeric systems capable of inducing MI. The filaments produced when orthogonal beams underwent simultaneous MI would align with themselves, forming highly ordered structures within the material. These interactions were used as the basis of an encoding and computing system based on the specific ordering of the resulting filaments. The mechanical properties of the resulting polymers were improved and tuned by developing a long-chain organosiloxane based system. The embedded waveguide structures are capable of guiding light when significantly deformed and restore to their initial parameters. A hydrogel system was also developed that was capable of producing self-trapping and MI with incoherent light. The samples were tested with biological systems and were also used to produce dynamic lens samples with enhanced angle of view. / Thesis / Doctor of Philosophy (PhD)

The synthesis and characterization of phosphorus containing poly(arylene ether)s were investigated to determine the effect of phosphorus upon the thermal stability, mechanical strength, and fire resistance of thermoplastics. Phosphorus containing activated aromatic dihalides and bisphenols were synthesized in high purity. These monomers were successfully polymerized via nucleophilic aromatic substitution to afford high molecular weight polymers. It was determined that by incorporating the phosphine oxide moiety into the polymer backbone certain properties of the resulting poly(arylene ether)s were substantially improved, such as an increase in T_g, thermal stability in air, modulus, and char yield, compared with control poly(arylene ether sulfone)s. The high char yields obtained for these polymers in air, along with observed intumescence indicates that these materials have improved fire resistance. Preliminary cone calorimetry measurements support this conclusion. In addition, the phosphine oxide group in the backbone was reduced to a phosphine and successfully converted to a phosphonium bromide ionomer. The resulting system was further chemically modified to ionically bond second-order nonlinear optical chromophores to the backbone of selected poly(arylene ether)s. Initial results on corona poling of cast film at low temperature produced stable second harmonic generation in these materials, indicating that they may have promise in nonlinear optical applications. / Ph. D.

No description available.

No description available.