Progress In Optics 45

EDITORIAL ADVISORY BOARD G.S. Agarwal Ahmedabad, India G. Agrawal Rochester, USA T. Asakura Sapporo, Japan A. Aspect Orsay, France M.V Berry Bristol, England A.T. Friberg Stockholm, Sweden VL. Ginzburg Moscow, Russia F. Gori Rome, Italy L.M. Narducci Philadelphia, USA J. Pefina Olomouc, Czech Republic R.M. Sillitto Edinburgh, Scotland H. Walther Garching, Germany Preface This volume contains six review articles on diverse topics that have become of particular interest to optical scientists and optical engineers in recent years. The first article, by N. Davidson and N. Bokor, reviews researches on the anamorphic shaping of laser beams and of diffuse light whose input or output is substantially elongated along one direction. Such elongated beams have come to be of special interest in recent years with the appearance of high-power laser diode bars, whose excellent properties are offset by their poor beam quality and by the fact that the output beam profile is highly anamorphic (with typical aspect ratio 1000:1) and hence unsuitable for many applications. Several techniques have been developed to collimate and shape the output beams of such laser diode bars into symmetric spots. Anamorphic beam shaping has also been used to concentrate symmetrical fields such as solar radiation into very narrow lines, for use in heating water pipes, for side-pumping solar lasers, and in optical metrology (e.g. for improving resolution in surface profile measurement and high-resolution spectrometry). The article presents a review of the main reflective, refractive, diffractive, and adiabatic techniques for anamorphic beam characterization. The second article, by I. Glesk, B.C. Wang, L. Xu, V Baby and P.R. Prucnal, presents a review of recent progress in the development of ultra-fast alloptical switching devices with various applications for future optical networks. The operation principle and performance of different all-optical switches based on nonlinearities in optical fiber semiconductor optical amplifiers (SOA) and passive waveguides are discussed. Special attention is paid to interferometric SOA-based all-optical switches. Several testbed demonstrations are described. The next article, by J. Yin, W. Gao and Y. Zhu, is concerned with the generation of dark hollow beams and their applications. Such beams have been used to form optical pipes, optical tweezers, atomic pipes, atomic tweezers, atomic refrigerators, and atomic motors. They can be applied in the accurate, non-contact manipulation and control of microscopic particles, such as biological cells, neutral atoms and molecules. The principles and experimental methods for generating various types of dark hollow beams are discussed. Applications of such beams in optical traps for microscopic particles including biological cells vi Preface are also discussed, as are recent studies of dark hollow beams in atom optics and coherent matter-wave optics. The fourth article, by D.J. Gauthier, presents a review of a new type of quantum oscillator known as two-photon laser. Such devices are based on twophoton stimulated emission processes whereby two photons incident on an atom induce it to drop to a lower energy state and four photons are scattered. This kind of laser has been realized only relatively recently by combining cavity quantum electrodynamics exper