Hywel Owen

NEW LOW MOLAR-MASS ORGANOSILOXANES WITH UNUSUAL FERROELECTRIC PROPERTIES

Abstract A new low molar mass chiral organosiloxane mesogen and its racemic analogue have been synthesized and their mesomorphic and ferroelectric properties investigated. The chiral derivative, denoted A∗B, exhibits one tilted enantiotropic ferroelectric smectic C mesophase over a broad temperature range, with very high tilt angles and moderate spontaneous polarization (36° and 19 nC cm−2 at 20°C). The achiral siloxane derivative, denoted A∗B, exhibits one broad enantiotropic smectic C phase. Preliminary electro-optic measurements indicate that the spontaneous polarization is weakly dependent on temperature between 10°C and 50°C, the latter being the S∗c to isotropic phase transition. The tilt angle and layer spacing are temperature independent, and current response times of less than 200 μs were measured at 25°C for fields of 10 V μ−1. These results are discussed in comparison with those for side chain polymer liquid crystal structures and other low molar mass ferroelectric materials.

A new series of low molar mass ferroelectric organosiloxanes with unusual electro-optic properties

Abstract A new series of low molar mass chiral organosiloxanes A*B, C*B and a racemic analogue A(±)B have been synthesised and their mesomorphic and ferroelectric properties investigated. A* and C* denote the mesogenic moiety and B denotes the pentamethyldisiloxane tail. The following organosiloxane materials have been prepared: C8A*B, C10A*B, racemic C10A(±)B and C10C*B, where the C8 or C10 prefix indicates the number of methylene spacers between A* and C* and A* contains a 4-[(S)-2methylbutanoyloxy] and C* contains a chloro chiral end group. C8A*B exhibits only an unstable monotropic mesophase, C10A*B and C10C*B both exhibit one tilted enantiotropic ferroelectric smectic-C mesophase over a broad temperature range, with high tilt angles and high spontaneous polarisation (e.g. C10C*B 28 ° and 150nCcm−2 at 20°C). The achiral siloxane derivative C10A(±)B, exhibits one broad enantiotropic smectic-C phase. Electrooptic measurements on C10A*B and C10C*B indicate that the spontaneous polarisation is only weakly...

FLUORESCENT DYE GUEST-HOST EFFECTS IN ADVANCED FERROELECTRIC LIQUID-CRYSTALS

Abstract Previous work has shown that guest-host ferroelectric systems incorporating dichroically absorbing dyes are suitable for use in colour display applications. These utilize either the dichroic absorption of a conventional dye, or the emission of a fluorescent dye. We present here the electrooptical properties of several advanced ferroelectric liquid crystals doped with a new fluorescent dye, coloured blue in emission. The data consists of measurements of tilt angle, response time, spontaneous polarization, and rotational viscosity, from which we conclude that certain hosts are not adversely affected by the fluorescent dopants. These results are then discussed in connection with the use of these mixtures in two novel colour display configurations, which are also presented, utilizing either the dichroic absorption or the polarized fluorescence of the fluorophore guests.

An XUV-FEL amplifier seeded using high harmonic generation

A detailed design of a free electron laser (FEL) amplifier operating in the extreme ultra violet (XUV) and seeded directly by a high harmonic source is presented. The design is part of the 4th generation light source (4GLS) facility proposed for the Daresbury Laboratory in the UK which will offer users a suite of high brightness synchronised sources from THz frequencies into the XUV. The XUV-FEL will generate photons with tunable energies from 8 to 100 eV at giga-watt peak power levels in near Fourier-transform limited pulses of variable polarisation. The designs of the high harmonic generation (HHG) seeding, FEL amplifier and synchronising systems are presented. Numerical simulations quantify the FEL output characteristics.

FLUORESCENT FERROELECTRIC LIQUID-CRYSTALLINE COPOLYACRYLATES

Abstract Fluorescent liquid crystalline side chain polymers were synthesized by copolymerization of a ferroelectric monomer and 5 per cent of various blue fluorescent naphthalic imide dye comonomers. Those copolymers were characterized by DSC, X-ray, GPC and optical microscopy. In favourable cases, fast switching fluorescent ferroelectric polymers resulted, exhibiting high tilt angles (up to ∼ 34°) and spontaneous polarization values (up to ∼ 115 nC cm−2) in the S*c phase. One fluorescent copolymer shows orthogonal smectic phases exclusively due to the structure of the incorporated fluorescent comonomer. In this case a strong electroclinic effect and high induced tilt angles (12° 10 V μm−1) have been observed in the Sa phase. Order parameters, S, of the dye moieties up to 0.64 were measured in the room temperature Sb phase for the copolymers

Technologies for Delivery of Proton and Ion Beams for Radiotherapy

Recent developments for the delivery of proton and ion beam therapy have been significant, and a number of technological solutions now exist for the creation and utilisation of these particles for the treatment of cancer. In this paper we review the historical development of particle accelerators used for external beam radiotherapy and discuss the more recent progress towards more capable and cost-effective sources of particles.

Prospects for a 4th Generation Light Source for the UK

A 4th Generation Light Source (4GLS) forms a major part of the new CASIM (Centre for Accelerator Science, Imaging and Medicine) project that has been proposed to be based at Daresbury Laboratory. Such a light source is envisaged to contain 3 free electron lasers (FELs) that are integrated with a highly optimised low energy synchrotron radiation source. The light source will be optimised to cover the photon energy range of 5 to 100 eV as well as being designed to host a cavity based FEL that would operate in the UV region. A second, linac based, infrared FEL would be placed in the same building thus enabling pump-probe experiments to be carried out with,state, of the art photon flux and brightness. The third FEL would not initially be a user facility but would be a linac based SASE FEL research project with the aim of producing ultra high brightness light in the VUV/SXR region. The primary source of 5 to 100 eV light could either be a storage ring or an energy recovery linac. Both options are presently being studied and a choice will be made by the Autumn of 2001. This paper describes the present concept for the 4GLS project and details the current status of the designs.

Electro-optic effects in novel siloxane containing oligomeric liquid crystals II: smectic C materials

A novel series of siloxane containing low molar mass liquid crystals have been synthesized and characterized by DSC, optical microscopy and electro-optic properties. The compounds described all exhibited room temperature bistable chiral smectic C phases. In this paper we concentrate on the electro-optic properties of both low (approximately 20 nC cm-2) and high (approximately 150 nC. cm-2) spontaneous polarization homologues. Data is also presented on tilt angles, response times and rotational viscosities for these compounds. All of the materials gave wide temperature range (> 50 degree(s)C) ferroelectric phases with tilt angles, varying between 28 degree(s) and 36 degree(s), that were independent of temperature. Response times of the order of microseconds, or longer, were observed. Dichroic dye guest-host mixtures were prepared and their unusual electro-optic properties leading to high contrast ratios also are described. The implications for both birefringence and dichroism based devices are considered.

4GLS: a new type of fourth generation light source facility

Consideration is now being given in the UK to the provision of an advanced facility at lower energy to complement the DIAMOND x-ray light source. The proposed solution, 4GLS, is a superconducting energy recovery linac (ERL) with an output energy around 600 MeV, delivering both CW beam currents up to 100 mA and alternatively high charge bunches for FEL applications. Production and manipulation of short electron bunches (fs) is a vital part of the source specification. In addition to beam lines from undulator sources in the ERL recovery path there will be three FELs: two will be oscillator types in the infrared and VUV respectively, and the third will be a high gain system for XUV output. The project is outlined, together with its status and the R&D challenges posed. A funded prototype based on a 50 MeV ERL is also described.

FAFNIR: Strategy and risk reduction in accelerator driven neutron sources for fusion materials irradiation data

Abstract The need to populate the fusion materials engineering data base has long been recognized, the IFMIF facility being the present proposed neutron source for this purpose. Re-evaluation of the regulatory approach for the EU proposed DEMO device shows that the specification of the neutron source can be reduced with respect to IFMIF, allowing lower risk technology solutions to be considered. The justification for this approach is presented and a description of a proposed facility, FAFNIR, is presented with more detailed discussion of the accelerator and target designs.