Superluminal behavior and the Minkowski space-time

Bessel X-waves, or Bessel beams, have been extensively studied in last years, especially with regard to the topic of superluminality in the propagation of a signal. However, in spite of many efforts devoted to this subject, no definite answer has been found, mainly for lack of an exact definition of signal velocity. The purpose of the present work is to investigate the field of existence of Bessel beams in order to overcome the specific question related to the definition of signal velocity. Quite surprisingly, this field of existence can be represented in the Minkowski space-time by a Super-Light Cone which wraps itself around the well-known Light Cone. So, the change in the upper limit of the light velocity does not modify the fundamental low of the relativity and the causal principle.Comment: 3 pages, 2 figure

Radially Self-Accelerating Beams

We report on optical non-paraxial beams that exhibit a self-accelerating behavior in radial direction. Our theory shows that those beams are solutions to the full scalar Helmholtz equation and that they continuously evolve on spiraling trajectories. We provide a detailed insight into the theoretical origin of the beams and verify our findings on an experimental basis

Hypergeometric-Gaussian Modes

We studied a novel family of paraxial laser beams forming an overcomplete yet nonorthogonal set of modes. These modes have a singular phase profile and are eigenfunctions of the photon orbital angular momentum. The intensity profile is characterized by a single brilliant ring with the singularity at its center, where the field amplitude vanishes. The complex amplitude is proportional to the degenerate (confluent) hypergeometric function, and therefore we term such beams hypergeometric gaussian (HyGG) modes. Unlike the recently introduced hypergeometric modes (Opt. Lett. {\textbf 32}, 742 (2007)), the HyGG modes carry a finite power and have been generated in this work with a liquid-crystal spatial light modulator. We briefly consider some sub-families of the HyGG modes as the modified Bessel Gaussian modes, the modified exponential Gaussian modes and the modified Laguerre-Gaussian modes

Characterization of vector diffraction-free beams

It is observed that a constant unit vector denoted by $\mathbf I$ is needed to characterize a complete orthonormal set of vector diffraction-free beams. The previously found diffraction-free beams are shown to be included as special cases. The $\mathbf I$-dependence of the longitudinal component of diffraction-free beams is also discussed.Comment: 8 pages and 2 figure

Characterization and modelling of the hollow beam produced by a real conical lens

The properties of the hollow beam produced by a conical lens are studied in detail. In particular, the impact of a rounded vertex is examined. It is shown that it could lead to drastic changes in the transverse distribution of the hollow beam, determined by the ratio between the transverse size of the incident beam and the size of the blunt area. An adequate choice for this ratio allows us to either minimize the losses or optimize the distribution symmetry.Comment: 13 pages, 10 figures, submitted to Optics Communication

For Piety, Virtue and Useful Knowledge: Maine’s Eighteenth-Century Academies

The article discussed the history of the first private academies in Maine in the later 17th and early 18th centuries

The Professional Air Traffic Controllers Strike: A Retrospective Analysis

The purpose of this study was to assess the opinions, beliefs, and perspectives of former air traffic controllers who were terminated from employment with the Federal Aviation Administration for participating in the Professional Air Traffic Controllers Organization (PATCO) strike of 1981. The study examines the perceptions of the former controllers to determine their feelings toward the justification for going on strike over 13 years ago. This is relevant in light of recent events including the lifting of the ban against rehiring PATCO controllers by the Clinton Administration. The data collected for this study were obtained with an opinionnaire mailed via a newsletter to former controllers who were members of the PATCO union. It was expected that a majority of the controllers would feel their actions of 1981 were justified. This feeling, however, would be mitigated by the fact that the controllers were terminated for their actions and sacrificed their careers with the decision to strike

Diffraction characteristics of optical elements designed as phase layers with cosine-profiled periodicity in azimuthal direction

The article concerns an investigation of the Fresnel diffraction characteristics of two types of phase optical elements, under Gaussian laser beam illumination. Both elements provide an azimuthal periodicity of the phase retardation. The first element possess azimuthal cosine-profiled phase changes deposited on a plane base. The second element is a combination of the first element and a thin phase axicon. The cosine profile of the phase retardation, of both diffractive elements, produces an azimuthal cosine-profiled modulation on their diffractograms. It destroys the vortex characteristics of their diffraction fields.Comment: 20 pages, submitted for publishin

China’s Antiship Ballistic Missile—Developments and Missing Links

That China is interested in an antiship ballistic missile seems a logical and natural outgrowth of its history of robust missile development. At what stage is its development? How near to operational readiness are its key components and technologies? What would be its implications for the U.S. Navy and the naval strategic balance between the United States and China