Splitting of femtosecond laser pulses by using a Dammann grating and compensation gratings

When a Dammann grating is used to split a beam of femtosecond laser pulses into multiple equal-intensity beams, chromatic dispersion will occur in beams of each order of diffraction and with different scale of angular dispersion because the incident ultrashort pulse contains a broad range of spectral bandwidths. We propose a novel method in which the angular dispersion can be compensated by positioning an m-time-density grating to collimate the mth-order beam that has been split, producing an array of beams that are free of angular dispersion. The increased width of the compensated output pulses and the spectral walk-off effect are discussed. We have verified this approach theoretically and validated it through experiments. It should be highly interesting in practical applications of splitting femtosecond laser pulses for pulse-width measurement, pump-probe measurement, and micromachining at multiple points. (c) 2005 Optical Society of America.

Three-dimensional superresolution by three-zone complex pupil filters

Complex pupil filters are introduced to improve the three-dimensional resolving power of an optical imaging system. Through the design of the essential parameters of such filters, the transmittance and radius of the first zone, three-dimensional superresolution is realized. The Strehl ratio and the transverse and axial gains of such filters are analyzed in detail. A series of simulation examples of such filters are also presented that prove that three-dimensional superresolution can be realized. The advantage of such filters is that it is easy to realize three-dimensional superresolution, and the disadvantage is that the sidelobes of the axial intensity distribution are too high. But this can be overcome by the application of a confocal system. (C) 2005 Optical Society of America.

High-efficiency reflective diffraction gratings in fused silica as (de)multiplexers at 1.55 mu m for dense wavelength division multiplexing application

We describe high-efficiency, high-dispersion reflection gratings fabricated in bulk fused Silica illuminated by incident lights in the C + L bands as (de)multiplexers for dense wavelength division multiplexing (DWDM) application. Based on the phenomenon of total internal reflection, gratings with optimized profile parameters exhibit diffraction efficiencies of more than 90% under TM- and TE-polarized incident lights for 101-nm spectral bandwidths (1520-1620 nm) and can reach an efficiency of greater than 97% for both polarizations at a wavelength of 1550 nm. Without loss of metal absorption, without coating of dielectric film layers, and independent of tooth shape, this new kind of grating should be of great interest for DWDM application. (C) 2005 Optical Society of America.

Polarization-dependent Talbot effect

The term "polarization-dependent Talbot effect" means that the Talbot self-imaging intensity of a high-density grating is different for TE and TM polarization modes. Numerical simulations with the finite-difference time-domain method show that the polarization dependence of the Talbot images is obvious for gratings with period d between 2 lambda and 3 lambda. Such a polarization-dependent difference for TE and TM polarization of, a high-density grating of 630 lines/mm (corresponding to d/lambda = 2.5) is verified through experiments with the scanning near-field optical microscopy technique, in which a He-Ne laser is used as its polarization is changed from the TE mode to the TM mode. The polarization-dependent Talbot effect should help us to understand more clearly the diffraction behavior of a high-density grating in nano-optics and contribute to wide application of the Talbot effect. (c) 2006 Optical Society of America.

Pulse shaping properties of volume holographic gratings in anisotropic media

Based on a modified coupled wave theory, the pulse shaping properties of volume holographic gratings (VHGs) in anisotropic media VHGs are studied systematically. Taking photorefractive LiNbO3 crystals as an example, the combined effect that the grating parameters, the dispersion and optical anisotropy of the crystal, the pulse width, and the polarization state of the input ultrashort pulsed beam (UPB) have on the pulse shaping properties are considered when the input UPB with arbitrary polarization state propagates through the VHG. Under the combined effect, the diffraction bandwidth, pulse profiles of the diffracted and transmitted pulsed beams, and the total diffraction efficiency are shown. The studies indicate that the properties of the shaping of the o and e components of the input UPB in the crystal are greatly different; this difference can be used for pulse shaping applications. (c) 2006 Optical Society of America.

Heterometallic Complexes as Models of Enzymatic Active Sites

This dissertation describes studies on two multinucleating ligand architectures: the first scaffold was designed to support tricopper complexes, while the second platform was developed to support tri- and tetrametallic clusters.

In Chapter 2, the synthesis of yttrium (and lanthanide) complexes supported by a tripodal ligand framework designed to bind three copper centers in close proximity is described. Tricopper complexes were shown to react with dioxygen in a 1:1 [Cu₃]/O₂ stoichiometry to form intermediates in which the O–O bond was fully cleaved, as characterized via UV-Vis spectroscopy and determination of the reaction stoichiometry. Pre-arrangement of the three Cu centers was pivotal to cooperative O₂ activation, as mono-copper complexes reacted differently with dioxgyen. The reactivity of the observed intermediates was studied with various substrates (reductants, O-atom acceptors, H-atom donors, Brønsted acids) to determine their properties. In Chapter 3, the reactivity of the same yttrium-tricopper complex with nitric oxide was explored. Reductive coupling to form a trans-hyponitrite complex (characterized by X-ray crystallography) was observed via cooperative reactivity by an yttrium and a copper center on two distinct tetrametallic units. The hyponitrite complex was observed to release nitrous oxide upon treatment with a Brønsted acid, supporting its viability as an intermediate in nitric oxide reduction to nitrous oxide.

In Chapter 4, a different multinucleating ligand scaffold was employed to synthesize heterometallic triiron clusters containing one oxide and one hydroxide bridges. The effects of the redox-inactive, Lewis acidic heterometals on redox potential was studied by cyclic voltammetry, unveiling a linear correlation between redox potential and heterometal Lewis acidity. Further studies on these complexes showed that the Lewis acidity of the redox-inactive metals also affected the oxygen-atom transfer reactivity of these clusters. Comparisons of this reactivity with manganese systems, collaborative efforts to reassign the structures of related manganese oxo-hydroxo clusters, and synthetic attempts to access related dioxo clusters are also described.

In Appendix A, ongoing efforts to synthesize new clusters supported by the same multinucleating ligand platform are described. Studies of novel approaches towards ligand exchange in tetrametallic clusters and incorporation of new supporting and bridging ligand motifs in trinuclear complexes are presented.

Talbot effect of a grating with different kinds of flaws

The Talbot effect of a grating with different kinds of flaws is analyzed with the finite-difference time-domain (FDTD) method. The FDTD method can show the exact near-field distribution of different flaws in a high-density grating, which is impossible to obtain with the conventional Fourier transform method. The numerical results indicate that if a grating is perfect, its Talbot imaging should also be perfect; if the grating is distorted, its Talbot imaging will also be distorted. Furthermore, we evaluate high-density gratings by detecting the near-field distribution with the scanning near-field optical microscopy technique. Experimental results are also given. (c) 2005 Optical Society of America.

Three-dimensional coupled wave study for finite-sized anisotropic volume holographic gratings under ultrashort pulsed beam readout

The three-dimensional coupled wave theory is extended to systematically investigate the diffraction properties of finite-sized anisotropic volume holographic gratings (VHGs) under ultrashort pulsed beam (UPB) readout. The effects of the grating geometrical size and the polarizations of the recording and readout beams on the diffraction properties are presented, in particular under the influence of grating material dispersion. The wavelength selectivity of the finite-sized VHG is analyzed. The wavelength selectivity determines the intensity distributions of the transmitted and diffracted pulsed beams along the output face of the VHG. The distortion and widening of the diffracted pulsed beams are different for different points on the output face, as is numerically shown for a VHG recorded in a LiNbO3 crystal. The beam quality is analyzed, and the variations of the total diffraction efficiency are shown in relation to the geometrical size of the grating and the temporal width of the readout UPB. In addition, the diffraction properties of the finite-sized and one-dimensional VHG for pulsed and continuous-wave readout are compared. The study shows the potential application of VHGs in controlling spatial and temporal features of UPBs simultaneously. (C) 2007 Optical Society of America

O bifrontismo do feminino em A Demanda do Santo Graal: Redescobrindo o substrato céltico das personagens femininas na busca do Santo Cálix

A figura da mulher ocupa significativo papel nas novelas de cavalaria do Ciclo Bretão. Emergindo como um elemento que traz liga às narrativas do lendário artúrico, constitui-se adjuvante essencial e multifacetada na construção dos episódios, numa interação constante com o masculino representado, principalmente, pelos cavaleiros. O Medievo traz à tona uma imagem matizada do feminino: a mulher socialmente vista sob clivagens diversas é refletida na literatura de cavalaria, conforme se pode verificar em A Demanda do Santo Graal. A presença feminina é importantíssima na narrativa, sobretudo na sua tensa relação com a cavalaria, agora ligada ao elemento religioso - monastizada, celibatária e ascética. O objetivo precípuo de nossos estudos é investigar de que maneira a fôrma sociocultural medieva, na qual foi moldada A Demanda do Santo Graal, se relaciona com seu substrato: as narrativas provindas da cosmovisão inerente ao imaginário céltico. Desta feita, nosso viés analítico verticaliza-se no elemento feminino presente na obra. Mais especificamente, toma-se por escopo a imagem de personagens que refletem a ideologia clerical moralístico-didatizante do século XIII, mas, sobretudo, resgata-se a imagem de personagens imbuídas de singular dualidade; ambigüidade esta que é marca não só do medievo paradoxal concernente ao feminino, mas também de personas literárias concebidas entre dois mundos, dois pólos ideológicos distintos. Em outros termos, fala-se de personagens que são seres ficcionais bifrontes: personagens localizadas entre as herdades e as identidades. Foram tomados como corpora de pesquisa os episódios em que estas damas polidimensionais aparecem e se tornam adjuvantes na ação literária, seja para cooperar, confundir ou prejudicar os cavaleiros que empreendem a sagrada, inefável e venturosa busca do Santo Cálix que dará fim às aventuras do Reino de Logres

Beam splitting of low-contrast binary gratings under second Bragg angle incidence

Beam splitting of low-contrast rectangular gratings under second Bragg angle incidence is studied. The grating period is between lambda and 2 lambda. The diffraction behaviors of the three transmitted propagating orders are illustrated by analyzing the first three propagating grating modes. From a simplified modal approach, the design conditions of gratings as a high-efficiency element with most of its energy concentrated in the -2nd transmitted order (similar to 90%) and of gratings as a 1 x 2 beam splitter with a total efficiency over 90% are derived. The grating parameters for achieving exactly the splitting pattern by use of rigorous coupled-wave analysis verified the design method. A 1 x 3 beam splitter is also demonstrated. Moreover, the polarization-dependent diffraction behaviors are investigated, which suggest the possibility of designing polarization-selective elements under such a configuration. The proposed concept of using the second Bragg angle should be helpful for developing new grating-based devices. (C) 2008 Optical Society of America.

Bragg diffraction of multilayer volume holographic gratings under ultrashort laser pulse readout

The multilayer coupled wave theory is extended to systematically investigate the diffraction properties of multilayer volume holographic gratings (MVHGs) under ultrashort laser pulse readout. Solutions for the diffracted and transmitted intensities, diffraction efficiency, and the grating bandwidth are obtained in transmission MVHGs. It is shown that the diffraction characteristics depend not only on the input pulse duration but also on the number and thickness of grating layers and the gaps between holographic layers. This analysis can be implemented as a useful tool to aid with the design of multilayer volume grating-based devices employed in optical communications, pulse shaping, and processing. (C) 2008 Optical Society of America

A agenda do desenvolvimento na promoção dos direitos humanos: uma análise da política externa brasileira no governo Lula

Os direitos humanos consolidaram um conjunto de valores ético-políticos considerados fundamentais para assegurar o respeito à dignidade do ser humano. A problemática do desenvolvimento é fundamental para as considerações de política externa de países como o Brasil. A consagração do Direito ao Desenvolvimento (DaD) como um direito humano desafia a divisão artificial dos direitos humanos e revela a evolução temática deste campo de estudo. Essa dissertação usa o instrumental dos direitos humanos para avaliar a relevância e a singularidade de algumas posições brasileiras. Após uma dissonância observada nos anos 1970, reflexo do ciclo autoritário por que passava o país, verificou-se postura cooperativa do Brasil nas proposições que versavam sobre o DaD. No mesmo sentido, observou-se que, conquanto não seja conceito recorrente no discurso oficial brasileiro, as posições do país, no que dizem respeito ao modelo de desenvolvimento defendido e aos direitos humanos, autorizam a inferência de que há uma harmonia em relação aos princípios fundamentais dispostos na Declaração sobre o DaD, de 1986. Da análise das posições brasileiras, tornou-se possível particularizar a política externa do governo Lula. Do levantamento das variáveis internas e externas que exercem influência sobre a formulação política do governo, bem como das iniciativas públicas e dos discursos oficiais, encontramos alguma evidência empírica no sentido de que a política externa brasileira para os direitos humanos, na administração de Luiz Inácio Lula da Silva, passa por um viés de promoção do desenvolvimento e de crítica à ordem internacional. A política se singulariza por incorporar uma dimensão de valores à crítica. Com isso, harmoniza-se com as posições defendidas pelo país nos plenários internacionais, onde o tema do DaD tem sido objeto de debate.

O quebra-nozes de Machado de Assis: crítica e nacionalismo

Esta tese visa a analisar três perspectivas nacionalistas oferecidas pela obra crítica de Machado de Assis. Buscamos, inicialmente, a feição intelectual do jovem Machado no interior do projeto romântico-nacionalista, com o qual estava alinhado e do qual se afastaria paulatinamente. Para tanto, foi cotejado, inicialmente, com dois militantes daquele nacionalismo defensivo: Santiago Nunes Ribeiro e Joaquim Norberto de Sousa Silva. Esse lugar de onde falava Machado ganha em definição num segundo momento, quando empreendemos a análise comparativa de seus textos com os de Macedo Soares e José de Alencar. Sobretudo entre 1859 e 1872, Machado de Assis construiria sua crítica teatral, tornando-se um paladino da comédia realista francesa. A primeira face nacionalista de sua crítica afirma-se nesse profundo envolvimento de Machado com o projeto de um teatro brasileiro pautado no potencial pedagógico da alta comédia. A segunda perspectiva nacionalista define-se à medida que se define o classicismo moderno de Machado, uma articulação muito pessoal de sua visão universalista com a já instaurada modernidade literária. Para a análise desse viés, usamos o corpus de sua crítica literária construída como gênero autônomo, oferecida convencionalmente ao público, por via da qual escritores e leitores se habilitariam a intervir na sociedade, cumprindo, patrioticamente, a missão para a qual a literatura os preparara. A partir de 1883, depois de quase cinco anos afastado da crônica, Machado a retoma, usando-a para exercitar, mais franca e assiduamente, uma particular teoria da cultura brasileira e, paralelamente, uma espécie de busca de nosso caráter nacional. Dessa forma, seu nacionalismo, numa terceira angulação, orienta-se para a experiência humana, que, entre incorporar o fundamento externo e resistir a ele, acaba por formar algo irremediavelmente brasileiro; essa crônica, portanto, carrega uma crítica de feição cultural, no sentido de Machado ter-se comprometido com significações e valores de nossa vida social. Ao examiná-lo como escritor que, inicialmente, se postou contra o colonialismo cultural; que, a seguir, se engajou num projeto civilizatório conduzido pelo teatro e pela literatura e que, por fim, investigou a sensibilidade coletiva brasileira a partir de suas representações culturais, esta tese faculta uma apreensão mais criteriosa das interseções entre os temas nacionalismo e Machado de Assis

DIFFERENTIAL GEOMETRICAL METHODS IN THE STUDY OF OPTICAL-TRANSMISSION (SCALAR THEORY) .1. STATIC TRANSMISSION CASE

Static optical transmission is restudied by postulation of the optical path as the proper element in a three-dimensional Riemannian manifold (no torsion); this postulation can be applied to describe the light-medium interactive system. On the basis of the postulation, the behaviors of light transmitting through the medium with refractive index n are investigated, the investigation covering the realms of both geometrical optics and wave optics. The wave equation of light in static transmission is studied modally, the postulation being employed to derive the exact form of the optical field equation in a medium (in which the light is viewed as a single-component field). Correspondingly, the relationships concerning the conservation of optical fluid and the dynamic properties are given, and some simple applications of the theories mentioned are presented.

DIFFERENTIAL GEOMETRICAL METHODS IN THE STUDY OF OPTICAL-TRANSMISSION (SCALAR THEORY) .2. TIME-DEPENDENT TRANSMISSION THEORY

By generalization of the methods presented in Part I of the study [J. Opt. Soc. Am. A 12, 600 (1994)] to the four-dimensional (4D) Riemannian manifold case, the time-dependent behavior of light transmitting in a medium is investigated theoretically by the geodesic equation and curvature in a 4D manifold. In addition, the field equation is restudied, and the 4D conserved current of the optical fluid and its conservation equation are derived and applied to deduce the time-dependent general refractive index. On this basis the forces acting on the fluid are dynamically analyzed and the self-consistency analysis is given.