525 research outputs found
50th anniversary of the laser
On July, 7, 1960 a press conference at Huyghes announced that Maiman had assembled and put into operation the first laser. It was the very pulsed ruby laser that everybody knows today. The announcement came as a bomb. Nobody expected that in an unknown laboratory, new to the race to build a laser, this result could be obtained. It was such an unexpected result that many still today mantain that the true laser was discovered at Bell by Shawlow. This result was achieved through a long story which passed by the Townes maser and many tentative experiments and discussions both in the USA and Soviet Union. In this special issue we present a collection of papers which provide further information as to what happened after Einstein introduced the concept of stimulated emission. The first paper is a short paper by Townes on the development of the physics of microwaves following the creation of the maser. When the laser came on the stage one of its properties was the inherent coherence of the emitted light. Emil Wolf's contribution enlights the early days of coherence to which he so much contributed and the very timely first Rochester Conference which was held on June 27-29, 1960 a few days before the Times announcement of the Maiman achievement. Important contributions were given by Soviet Scientists and, Svetlana Lukishova's contributions helps us understand the work of Valentin Fabrikant which was mostly unknown to western scientists. At the end of his life, Maiman went to Vancouver in Canada and Andrew H. Rawicz gives his testimoniancy of his friendship there. Coherence and the statistical properties of laser light were much studied and we have two exceptional papers by Roy Pike and Jan Perina discussing these arguments. The issue also contains three more papers presenting some earlier achievements in the construction of multiquantumwell laser (M. L. Dotor, P. Huertas, P. A. Postigo, D. Golmayo and F. Briones), the first measurements on very short pulses (H. P. Weber and R. Dandliker) and spatial coherence (D. P. Barato and M. L. Calvo)
Management of the orbital angular momentum of vortex beams in a quadratic nonlinear interaction
Light intensity control of the orbital angular momentum of the fundamental
beam in a quadratic nonlinear process is theoretically and numerically
presented. In particular we analyzed a seeded second harmonic generation
process in presence of orbital angular momentum of the interacting beams due
both to on axis and off axis optical vortices. Examples are proposed and
discussed
Random nonlinear layered structures as sources of photon pairs for quantum-information processing
Random nonlinear layered structures have been found to be a useful source of
photon pairs with perfectly indistinguishable un-entangled photons emitted into
a very narrow spectral range. Localization of the interacting optical fields
typical for random structures gives relatively high photon-pair fluxes.
Superposing photon-pair emission quantum paths at different emission angles,
several kinds of two-photon states (including states with coincident
frequencies) useful in quantum-information processing can easily be generated.Comment: 4 pages, 5 figure
Influence of pump-field scattering to nonclassical-light generation in a photonic band-gap nonlinear planar waveguide
Optical parametric process occurring in a nonlinear planar waveguide can
serve as a source of light with nonclassical properties. Properties of the
generated fields are substantially modified by scattering of the nonlinearly
interacting fields in a photonic band-gap structure inside the waveguide. A
quantum model of linear operator amplitude corrections to amplitude mean-values
provides conditions for an efficient squeezed-light generation as well as
generation of light with sub-Poissonian photon-number statistics. Destructive
influence of phase mismatch of the nonlinear interaction can fully be
compensated using a suitable photonic-band gap structure inside the waveguide.
Also an increase of signal-to-noise ratio of an incident optical field can be
reached in the waveguide.Comment: 10 pages, 12 figure
A note on the history of photoacoustic, thermal lensing, and photothermal deflection techniques
We review the history of photoacoustic, thermal lensing, and photothermal deflection techniques from early experiments to the current time. The paper also describes the main fields of application in chronological order, showing the primary advantages and listing initial technological development
Modeling the effects of variable feeding patterns of larval ticks on the transmission of Borrelia lusitaniae and Borrelia afzelii
Spirochetes belonging to the Borrelia burgdoferi sensu lato (sl) group cause
Lyme Borreliosis (LB), which is the most commonly reported vector-borne
zoonosis in Europe. B. burgdorferi sl is maintained in nature in a complex
cycle involving Ixodes ricinus ticks and several species of vertebrate hosts.
The transmission dynamics of B. burgdorferi sl is complicated by the varying
competence of animals for different genospecies of spirochetes that, in turn,
vary in their capability of causing disease. In this study, a set of difference
equations simplifying the complex interaction between vectors and their hosts
(competent and not for Borrelia) is built to gain insights into conditions
underlying the dominance of B. lusitaniae (transmitted by lizards to
susceptible ticks) and the maintenance of B. afzelii (transmitted by wild
rodents) observed in a study area in Tuscany, Italy. Findings, in agreement
with field observations, highlight the existence of a threshold for the
fraction of larvae feeding on rodents below which the persistence of B. afzelii
is not possible. Furthermore, thresholds change as nonlinear functions of the
expected number of nymph bites on mice, and the transmission and recovery
probabilities. In conclusion, our model provided an insight into mechanisms
underlying the relative frequency of different Borrelia genospecies, as
observed in field studies.Comment: 14 pages, 3 figures, to be published in Theoretical Population
Biolog
Optimization of thermochromic VO2 based structures with tunable thermal emissivity
In this paper, we design and simulate VO2/metal multilayers to obtain a large tunability of the thermal emissivity of infrared (IR) filters in the typical mid wave IR window of many infrared cameras. The multilayer structure is optimized to realise a low emissivity filter at high temperatures useful for military purposes. The values of tunability found for VO2/metal multilayers are larger than the value for a single thick layer of VO2. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4739489
Light scattering from a rough metal surface: theory and experiment
There is still great interest in the determination of microtopographic properties of rough metallic surfaces from light scattering measurements. According to Beckmann–Kirchhoff theory a clear relationship is established between the in-plane angular scattered light intensity and the statistical properties of the surface. We discuss one way to invert this relationship, and we introduce a new iterative procedure to retrieve the height autocorrelation function even for a very rough metallic surface (rms surface roughness of the same order of the optical wavelength). The procedure is eventually applied to the experimental data of a known metallic surface for validation
Properties of entangled photon pairs generated in one-dimensional nonlinear photonic-band-gap structures
We have developed a rigorous quantum model of spontaneous parametric
down-conversion in a nonlinear 1D photonic-band-gap structure based upon
expansion of the field into monochromatic plane waves. The model provides a
two-photon amplitude of a created photon pair. The spectra of the signal and
idler fields, their intensity profiles in the time domain, as well as the
coincidence-count interference pattern in a Hong-Ou-Mandel interferometer are
determined both for cw and pulsed pumping regimes in terms of the two-photon
amplitude. A broad range of parameters characterizing the emitted
down-converted fields can be used. As an example, a structure composed of 49
layers of GaN/AlN is analyzed as a suitable source of photon pairs having high
efficiency.Comment: 14 pages, 23 figure
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