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Research was conducted to examine the non-steady-state photoelectromotive force in reduced lithium niobate crystals. Non-steady-state photoelectric currents are usually generated by oscillating interference patterns. The photocurrents were observed to strongly decline for frequencies above 2 Hz. The approach may be relevant for material characterization and for convenient active stabilization of holographic setups against mechanical vibrations.

The development of holographic storage for computer-generated information is being inhibited by the problems associated with the read-out phase because the stored data is destroyed by homogenous illumination. A new study investigates the use of two-colour holography. The lithium niobate crystal is doped with iron and manganese deep electron traps. The presence of UV light causes the data to be stored as red-light interference pattern, allowing it to be read, without erasure, in the absence of UV light.

The influence of ultraviolet (UV) light (wavelengths λ=334 and 305 nm) on the ferroelectric domain inversion of lithium niobate crystals doped with different amounts of magnesium ranging from 0 to 7.5 mol % is investigated. Illumination at λ=334 nm leads to a coercive field reduction of up to 50%, but only in samples doped with a magnesium concentration above the so-called optical damage threshold. For λ=305 nm the effective coercive field is reduced significantly in all samples. Different behavior of the coercive field reduction at both wavelengths indicates the presence of two mechanisms. To explain the effect occurring for 305 nm illumination a model is presented in which an UV-induced photoconductivity alters the electric-field distribution through the crystal thickness. Utilizing an UV-interference pattern and a suitable homogeneous external electrical field, periodically poled lithium niobate with a period length of 55 μm is produced. [ABSTRACT FROM AUTHOR]

Periodically poled lithium niobate crystals are investigated by illumination along the crystallographic c axis while applying an external electric field. The resulting diffraction patterns are in good agreement with the results of numerical simulations and directly yield first information such as periodicity, duty cycle, and homogeneity of the domain patterns. [ABSTRACT FROM AUTHOR]

Ferroelectric domain reversal by electric field poling of lithium niobate crystals (LiNbO3) with varying stoichiometry and magnesium (MgO) doping level obtained from various commercial suppliers is investigated. Magnesium doping lowers the domain-wall velocity, increases the uniformity of the growth of the domains, and reduces the impact of crystal symmetry on the shape of the domains. Illumination with ultraviolet (UV) laser light (305 nm) reduces the coercive field by up to 34% in MgO-doped crystals, but is accompanied by a degradation of poling quality. UV light of longer wavelengths (334 nm) has no influence on the coercive field except for the MgO:LiNbO3 material of one supplier, where the field is reduced by 27%. In this case the poling quality is excellent. UV-induced reduction of stress-induced birefringence is observed in some samples. The results are of crucial relevance for light-induced domain engineering of LiNbO3 crystals. [ABSTRACT FROM AUTHOR]

In this article, we present pyroelectric investigations of electrically poled side-chain polymers containing mesogenic disazobenzene chromophores using a very simple setup. Heating above the glass temperature (about 104°C) usually eliminates the pyroelectric effect of the sample. However, in samples with an indium tin oxide/aluminum electrode design, a self-poling effect is observed. The pyroelectric coefficients of electrically poled samples reach values of up to 0.2 μC/(m²K). From this, we conclude that the strongly anisometric side chains can be reoriented, and that their degree of alignment is about 3%. [ABSTRACT FROM AUTHOR]

We present experimental data showing a significant dependence of light absorption on temperature in photorefractive LiNbO[sub 3]:Fe crystals. The results are successfully explained by assuming that the widths of the Fe[sup 2+] absorption bands in the visible and in the infrared spectral region depend on temperature. The findings are of relevance for thermal fixing of holograms. Furthermore, a temperature-induced increase of the infrared absorption is promising for improved infrared recording. [ABSTRACT FROM AUTHOR]

Cerium-doped lithium niobate crystals are tested for holographic recording. A photochromic effect is observed in crystals doped with cerium and manganese. But two-center recording in the sample is not as effective as in iron and manganese doubly doped crystals. Photocurrent measurements in cerium and iron singly doped crystals indicate that the photovoltaic constant in the cerium-doped crystal is only one third of that of the iron-doped one. This is the main reason accounting for the low sensitivity of cerium-doped lithium niobate crystals. However, in the diffusion dominated case, i.e., for reflection geometry, cerium-doped lithium niobate may give a strong effect. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents a method for performing direct photoconductivity measurements of Sr0.61Ba0.39Nb2O6:Ce crystals at high intensities. Electronic circuit used in the study; Ohmic behavior; Dependence of photoconductivity on light intensity; Dependence on the cerium concentration.

A detailed investigation of the charge-transport properties and of photorefractive performance of BCT:Fe crystals is performed. The main outcome of the investigation was that at typical intensities all charge transport processes were very well explained within a one-center model.

Cerium-doped lithium niobate crystals are tested for holographic recording and a photochromic effect is observed in crystals in doped with cerium and manganese. Photocurrent measurements in cerium and iron singly doped crystals indicate that the photovoltaic constant in the cerium-doped crystal is only one third of that of that of the iron-doped one.

This is the second of a two-part review of global public-private partnerships (GPPPs) for health development. Part I was published in the April issue of the Bulletin(Vol. 78, No.4). The recent emergence of GPPPs is rapidly reconfiguring the international health landscape. While most multilateral and bilateral agencies are currently grappling with how to proceed, there is little information in the public domain concerning how individual partnerships work and to date very little consideration of the many implications of this trend. This paper differentiates between product-based, product development-based and issues/systems-based GPPPs and describes a number of examples of each type in the health sector. The benefits of these initiatives, not least the major resources which they harness for specific health problems, are identified. The final section of the paper explores the implications and dilemmas posed by GPPPs. It discusses whether or not shared goals can transcend conflicting values and mandates and how governance of partnership arrangements may transform and undermine certain attributes of multilateral organizations. The paper concludes that the current climate of goodwill between public and private sectors offers an opportunity that should not be missed: it can be used not only to foster new partnership but to ensure that partnership is truly in the interests of international public health. Keywords: world health, trends; intersectoral cooperation, history; public sector; private sector; United Nations; developing countries., Voir page 708 le resume francais. En la pagina 708 figura un resumen en espanol. Introduction In Part I of this article, which appeared in the last issue of the [...]

Voir page 558 le resume en francais. En la pagina 559 figura un resumen en espanol. Introduction The latter half of the 1990s witnessed a burgeoning number of initiatives involving [...], The proliferation of public-private partnerships is rapidly reconfiguring the international health landscape. This article (part I of two on the subject) traces the changing nature of partnership, and discusses the definitional and conceptual ambiguities surrounding the term. After defining global public-private partnerships (GPPPs) for health development, we analyse the factors which have led to the convergence of public and private actors and discuss the consequences of the trend toward partnership between UN agencies (including the World Bank) and commercial entities in the health sector. Generic factors such as globalization and disillusionment with the UN, and factors specific to the health sector, such as market failure in product development for orphan diseases, are examined. Reviewed are the interests, policies, practices and concerns of the UN, the private-for-profit sector, bilateral organizations, and governments of low-income countries with respect to public-private partnership. While GPPPs bring much needed resources to problems of international health, we highlight concerns regarding this new organizational format. Part II, which will be published in the May issue of the Bulletin, presents a conceptual framework for analysing health GPPPs and explores the issues raised. Keywords: world health, trends; intersectoral cooperation, history; public sector; private sector; United Nations; public policy.