The phase diagram of superfluid 3He is predicted to be modified when confined to a regular geometry of size comparable to the superfluid coherence length. This thesis addresses the problem of the effect of such a small geometry on the order parameter of the superfluid. The samples are probed by two methods: Nuclear Magnetic Resonance and a Torsional Oscillator. Nuclear Magnetic Resonance provides information about the spin dynamics of the system. This information can be used to identify the superfluid phases. The damping and frequency change of the torsion pendulum determine the hydrodynamic response of the fluid and they can be used to identify superfluidity and measure the superfluid density. The bulk anisotropy of the superfluid density could potentially help to identify the A-phase, although information sufficient to unambiguously determine the particular superfluid phase from the torsional oscillator is probably not possible in our experiment. The NMR experiment involved the construction of a high sensitivity SQUID spectrometer which allowed the observation of samples of the order of 1 x 1017 spins. We observed superfluidity in a variety of samples. The superfluid phases were identified as A- and B-phases in small droplets distributed over the experimental cell. These droplets were formed due to imperfect annealing of the samples. For a 3 Jlm thick slab we observed a strongly supercooled A-phase at temperatures as low as f-)0.38 mK. This A-phase suddenly underwent a transition into B-phase after a period of ",,20 hours independently of the temperature to which it had been supercooled. With the torsional oscillator we could see superfluidity in a film of nominal thickness of 143 nm. The dependence of the superfluid density on temperature agreed with most of the previous work, theoretical and experimental alike. It also showed remarkable similarities with other disordered systems like superfluid 3He in aerogel, although these similarities were not quantitative

Liquid crystal displays are intricate devices which consist of many cells that are filled with liquid crystal hosts. The operation of the liquid crystal cell is to modulate the polarisation of light, by varying their birefringence, which in turn can be used to control the intensity of light and colour as a function of time. Many individual cells grouped together can be controlled to give specific intensity of light and colour, to build up images that are viewed on displays, i.e. pictures on TV’s. The properties of the liquid crystalline material used in a cell dictate the performance of the device which they are used. Commercially used liquid crystal material is typically a multi-component system that exhibits many physical properties such as birefringence, dielectric anisotropy, voltage holding ratio, visco-elastic, guest-host effect and the kinetic switching response time of the cell between the on state and off state. By manipulating the physical properties we can exert specific control over the properties of the cell of particular importance in display applications is the speed with which cells can be turned between the on and off state; these are known as the rise and decay response times respectively. Introducing guest molecules into the liquid crystal host may alter the dielectric anisotropy which potentially increases the speed of the switching process, making the device faster. Guest molecules must be compatible with the dielectrically positive or negative liquid crystal host allowing good mixing of the components and alignment between the guest molecule and liquid crystal molecule. This compatibility is important as it allows both, guest and host, to align with the applied electric field when turned on giving the on state of the cell and when turned off allowing both to re-align with the alignment layer in the cell bringing to the cell order of the medium back to the off state of the cell. The time taken for the cell to reach the on state and off state is an important part of this study. Dopants have been designed with a head, tail and linker core moiety that are compatible with dielectrically positive and negative liquid crystals. Head groups will have polar substituents such as heteroarenes, fluorine and bromine, to exert control over the dielectric anisotropy. Alkoxy or alkyl tails were selected to increase solubility and size compatibility with the liquid crystal hosts. The linkers between the two arenes were selected as acetylene (linear, large Raman cross-section) and ether, methylene and propylene (to bring about a bend in the molecule). The switching times for liquid crystal devices are studied using an electro-optic method developed in conjunction with SONY MSL (Stuttgart). These studies enable analysis of the transmission of light through the cell as it goes from the on/off state as a function of time and applied potential. By comparison with the currently used liquid crystal materials our work shows that the level of doping, the length of the tail and the nature of the linker do affect the switching time significantly. It is shown that a non-linear linker, which introduces a ‘bite angle’ within the guest molecule brings about the best increase in response times. Time-Resolved Raman spectroscopy studies of a liquid crystal cell during the turn on/off process were made. These demonstrate the capability of this technique to measure the orientation of the molecules as a function of time as well allowing the independent motion of the guest and host molecules during the switching process. Raman spectroscopy gives a useful insight into the behaviour of the guest and host materials in an operating liquid crystal cell.

Polymer Dispersed Liquid Crystals (PDLCs) are attracting considerable attention for new optical displays. This thesis describes the synthesis of PDLC materials, fabrication of cells and study of their optical and dielectric behaviour. This work includes two areas of research. Predominantly it is an investigation of the properties of PDLCs prepared using Polymerisation Phase Separation (PIPS) by UV irradiation of mutually soluble liquid crystal (LC) and pre-polymer materials, developed for use in PDLC systems. A limited study of liquid crystal gels completes the thesis. We demonstrate that the electro-optical response of a PDLC is due to alignment of the LC phase, illustrated by comparison of the dielectric behaviour of the PDLC and LC in an aligning field. It is evident from this work that there is solubility of the LC component in the polymer that forms the continuous phase. Therefore, only at higher concentrations of the LC component (above 30%) will the PDLC be formed, and in such materials, the continuous phase contains dissolved LC material. Variation of experimental conditions under which samples are prepared, by changing the composition, temperature of cure and the presence of aligning fields, leads to modifications in the structure and properties of PDLCs, which are investigated. Techniques to study the dielectric, electro-optic and optical properties have been applied to the range of samples prepared. Such studies give information on the alignment of the LC phase in a PDLC in directing electric fields. It is demonstrated that dielectric relaxation spectroscopy (DRS) provides direct information on the macroscopic orientation and voltage induced changes in the alignment of gels produced in the presence and absence of electric fields. Our studies show that DRS, in combination with optical techniques, provides a powerful means for studying the alignment of LC molecules in PDLCs and gels.

In the past, liquid crystal alignment has been achieved through a surface alignment technique. Before the liquid crystal (LC) cell is fabricated, the two substrates are coated with a thin film of polymer which is then rubbed with a nylon cloth. The process is difficult to control, leads to the formation of electrostatic charge at the film surface and can induce only one type of alignment within a LC cell. A surface-alignment technique has been developed in which a polymer coated substrate is prepared not through a rubbing process but by a linear photopolymerisation (LPP) reaction. A substrate is coated with a thin film of a photoactive polymer. Illumination with plane polarised UV light causes the polymer to undergo a side-chain cross-linking reaction. The plane polarised nature of the UV light produces an anisotropic distribution of un-reacted side-chains. It is thought that these residual side-chains induce alignment in a liquid crystal phase. Using glass, ITO-coated glass and quartz substrates, we have fabricated LC cells by sandwiching a nematic phase between (i) two LPP treated substrates; or (ii) one LPP treated substrate and one conventional rubbed polymer (RP) treated substrate. The relative aligning strength of the LPP and RP treated substrates were studied qualitatively using <B>optical microscopy</B> and quantitatively using an <B>optical transmission</B> experiment and <B>dielectric relaxation spectroscopy</B>. It was found that in terms of both azimuthal and zenithal aligning strength, the RP treated substrates were more effective at aligning a nematic phase than the LPP treated surfaces. Liquid crystal alignment using a photoactive substrate leads to the possibility of <I>patterning </I>a LC cell with pixels that appear optically different when viewed between polarizers. Patterned LC cells could have enormous and wide-ranging applications in the display, electrooptical element and information storage industries. We have shown that high-density, controllable patterning can be achieved in LC cells incorporating a LPP treated surface.

Accepted analogies between matter waves and electromagnetic waves are extended in order to show that matter waves should have mechanical properties. A semiclassical description of the continuity equations describing these mechanical properties is presented and a general expression for their flux density is obtained. A semiclassical detection theory for matter waves is developed, drawing upon the theory of photoelectron detection and the conservation equations from fluid mechanics. It is the intrinsically dispersive nature of matter waves which is important in deriving such a theory. It is shown that the detection rate can be related to the flux of particles through the detector surface. A fully quantum matter wave detection theory is also presented, beginning from a microscopic description of detection. Both the short-time approximation to the detection rate and its long-time correction are developed. Again it is shown that the detection rate can be related to the flux through the detector surface. The relative phase fluctuations of two one-dimensional condensates coupled along their whole length with a local single-atom interaction is examined. The thermal equilibrium is defined by the competition between independent longitudinal thermally excited phase fluctuations and the coupling between the condensates which locally favours identical phase. The relative phase fluctuations and their correlation length are computed as a function of the temperature and the strength of the coupling. Finally, the future potential of the work contained herein is examined.

No description available.

Ultra-cold atomic gases are formidable systems to investigate fundamental phenomena occurring in many-body quantum physics. In combination with scattering resonances and optical potentials, degenerate quantum gases provide new insight into strongly correlated systems and their characteristic properties. Notably, the admixture of impurity atoms to a Bose-Einstein condensate (BEC) has recently extended the physics of ultra-cold atoms into the area of quantum impurity problems.

No description available.

This dissertation describes the investigation of three novel schemes for the enhancement of fast liquid-crystal (LC) electro-optic effects using Fabry-Perot (F-P) cavities. The objective is to develop low voltage and high speed electro-optic modulators for use in free-space optical interconnects in silicon Very-Large-Scale-Integrated (VLSI) electronic systems. These optical interconnects are under active development as a potential technology to overcome the limitations associated with electrical interconnects. The prime candidate as the LC electro-optic effect for this application is the electroclinic effect associated with Smectic A * LCs (SmA*LCs) due to its potentially very fast response time in the order of nanoseconds. However, this effect is often very small which leads to either low contrast ratios or low throughputs using the conventional structures with a LC between crossed polarisers. Hence it is proposed to enhance this effect using F-P cavities as has been done for other small electro-optic effects such as those used in Multiple Quantum Wells. Due to the lack of refractive index change experienced by the light at normal incidence under applied electric fields, SmA*LCs cannot be used in F-P cavities directly to give intensity modulation. Two indirect techniques have been developed during this research to overcome this obstacle. The first technique developed involves the use of a Compound-Variable-Retarder (CVR) consisting of two independent quarter-wave plates (one being a SmA*LC) inside an asymmetric F-P (or Gires-Tournois) cavity which is placed between crossed polarisers. The CVR is used in order to induce an analogue phase change at normal incidence. The second technique developed involves the use of oblique incidence in order to induce an analogue change of the effective extraordinary refractive index experienced by the incident light. The structure in this case consists simply of a SmA*LC layer inside a F-P cavity. Original proof-of-principle experiments have been developed and have verified both proposed schemes, which can offer high enhancement and have potential for free-space optical interconnects.

No description available.