Ion-implanted lanthanum fluoride waveguides

The effects of He+ and H+ implantation into LaF3 substrates have been investigated at both room temperature and 77 K. At room temperature the surface of the samples becomes black, possibly due to chemical reduction effects, but at low temperature the crystals remain clear and a refractive index change is observed which produces a surface waveguide. The dark mode spectra of these guides have been recorded using the prism coupling technique, and their refractive index profiles have been deduced from the spacing of these modes. The ion implantation produces a thin optical barrier layer of low refractive index at the end of the ion range. This paper discusses the use of multiple-energy implantation to produce a broad optical barrier in order to reduce the tunnelling losses of the guides, and subsequent thermal annealing to reduce absorption and scattering losses caused by colour centre formation in the electronic stopping surface region of the guides. It is concluded that either single- or multiple-energy He+ implants can be ideally used to form waveguides, for applications in the blue/UV or red/IR wavelength regions, respectively, with losses of a few dB/cm

Gain reversal studies in photorefractive waveguides

We report on low-loss photorefractive BaTiO3 H+ implanted waveguides exhibiting reversal of two-beam-coupling gain direction, caused by induced colour centres. The anomalous two-beam-coupling gain has been investigated as a function of the input beam ratio

Photorefractive planar waveguides in BaTiO₃ fabricated by ion-beam implantation

For the first time to our knowledge, photorefractive properties have been observed in planar waveguides fabricated by the technique of ion-beam implantation in BaTiO3 single crystals. The implantation was carried out by using 1.5 MeV H+ ions at a dose of 10-16 ions/cm2. For a given input power, a decrease in the effective photo-refractive two-beam coupling response time of ≥102 has been observed, owing to a combination of optical confinement within the waveguide and possible modification of charge-transport properties induced through implantation. Experiments carried out on the two-beam coupling gain show that the gain direction has been reversed in the waveguide compared with that of the bulk crystal

BaTiO₃ waveguide self-pumped phase conjugator

For the first time to our knowledge, self-pumped phase conjugation is reported in a planar waveguide structure in a BaTiO3 single crystal. The waveguide was fabricated by the technique of ion implantation, with 1.5-MeV H+ ions at a dose of 1016 ions/cm2. Phase-conjugate reflectivities >20% have been measured for waveguide self-pumped phase conjugation, and, for a given input power, an order-of-magnitude reduction in the response time is observed in the waveguide compared with the bulk. The fidelity of phase conjugation in the guide is also discussed

Ion-implanted Nd:MgO:LiNbO₃ planar waveguide laser

Laser oscillation in an ion-implanted planar Nd:MgO:LiNbO3 waveguide is demonstrated for the first time to our knowledge. Details of the waveguide structure, spectroscopic properties, photorefractive effects. and laser performance are given. A simple calculation of the absorbed power threshold gives ~8mW, in fair agreement with the experimental value of ~17mW

A terminal assessment of stages theory : introducing a dynamic states approach to entrepreneurship

Stages of Growth models were the most frequent theoretical approach to understanding entrepreneurial business growth from 1962 to 2006; they built on the growth imperative and developmental models of that time. An analysis of the universe of such models (N=104) published in the management literature shows no consensus on basic constructs of the approach, nor is there any empirical confirmations of stages theory. However, by changing two propositions of the stages models, a new dynamic states approach is derived. The dynamic states approach has far greater explanatory power than its precursor, and is compatible with leading edge research in entrepreneurship

Weber and church governance: religious practice and economic activity

The debate about the relationship between religion and economic activity in the wake of Weber has been cast largely in terms of belief and values. This article suggests an alternative focus on practice. It argues that taken for granted practices of church governance formed to-hand resources for the organization of economic activity. The argument is developed through an examination of the historical development of church governance practices in the Presbyterian Church of Scotland, with particular emphasis on the way in which theological belief gave rise to practices of accountability and record keeping. In turn such practices contributed to a ‘culture of organization’ which had implications for economic activity. A focus on governance practices can help to illuminate enduring patterns of difference in the organization of economic activity

An Examination of Chimpanzee Use in Human Cancer Research

Advocates of chimpanzee research claim the genetic similarity of humans and chimpanzees make them an indispensable research tool to combat human diseases. Given that cancer is a leading cause of human death worldwide, one might expect that if chimpanzees were needed for, or were productive in, cancer research, then they would have been widely used. This comprehensive literature analysis reveals that chimpanzees have scarcely been used in any form of cancer research, and that chimpanzee tumours are extremely rare and biologically different from human cancers. Often, chimpanzee citations described peripheral use of chimpanzee cells and genetic material in predominantly human genomic studies. Papers describing potential new cancer therapies noted significant concerns regarding the chimpanzee model. Other studies described interventions that have not been pursued clinically. Finally, available evidence indicates that chimpanzees are not essential in the development of therapeutic monoclonal antibodies. It would therefore be unscientific to claim that chimpanzees are vital to cancer research. On the contrary, it is reasonable to conclude that cancer research would not suffer, if the use of chimpanzees for this purpose were prohibited in the US. Genetic differences between humans and chimpanzees, make them an unsuitable model for cancer, as well as other human diseases