Narrow Results

We investigate the propagation of light rays and evolution of optical scalars in gauge theories of gravity where torsion is present. Recently, the modified Raychaudhuri equation in the presence of torsion has been derived. We use this result to derive the basic equations of geometric optics for several different interesting solutions of the Poincaré gauge theory of gravity. The results show that the focusing effects for neighboring light rays will be different than general relativity. This in turn has practical consequences in the study of gravitational lensing effects and also in determining the angular diameter distance for cosmological objects.

The genesis of special relativity is intimately related to the development of the theory of light propagation. When optical phenomena were described, there are typically two kinds of theories: (i) One based on light rays and light particles and (ii) one considering the light as waves. When diffraction and refraction were experimentally discovered, light propagation became more often described in terms of waves. Nevertheless, when attempts were made to explain how light was propagated, it was nearly always in terms of a corpuscular theory combined with an ether, a subtle medium supporting the waves. Consequently, most of the theories from Newton's to those developed in the 19th century were dual and required the existence of an ether. We therefore used the ether as our Ariadne thread for explaining how the principle of relativity became generalized to the so-called Maxwell equations around the 1900's. Our aim is more to describe how the successive ideas were developed and interconnected than framing the context in which these ideas arose.

Light propagation in a medium is sensitively dependent on the shape and intensity of the optical pulse as well as on the electronic and vibrational structure of the basic molecular units. We review in this paper the results of systematic studies of this problem for isotropic media. Our theoretical approach—the quantum mechanical–electrodynamical (QMED) approach—is based on a quantum mechanical account of the many-level electron-nuclear medium coupled to a numerical solution of the density matrix and Maxwell's equations. This allows us to accommodate a variety of nonlinear effects which accomplish the propagation of strong light pulses. Particular attention is paid to the understanding of the role of coherent and sequential excitations of electron-nuclear degrees of freedom. The QMED combination of quantum chemistry with classical pulse propagation enables us to estimate the optical transmission from cross sections of multi-photon absorption processes and from considerations of propagation effects, saturation and pulse effects. Results of the theory suggest that in the nonlinear regime, it is often necessary to simultaneously account for coherent one-step and incoherent step-wise multi-photon absorption, as well as for off-resonant excitations even when resonance conditions prevail. The dynamic theory of nonlinear propagation of a few interacting intense light pulses is highlighted here in a study of the optical power limiting with platinum-organic molecular compounds.

Light has been clinically utilized as a stimulation in medical treatment, such as Low-level laser therapy and photodynamic therapy, which has been more and more widely accepted in public. The penetration depth of the treatment light is important for precision treatment and safety control. The issue of light penetration has been highlighted in biomedical optics field for decades. However, quantitative research is sparse and even there are conflicts of view on the capability of near-infrared light penetration into brain tissue. This study attempts to quantitatively revisit this issue by innovative high-realistic 3D Monte Carlo modeling of stimulated light penetration within high-precision Visible Chinese human head. The properties of light, such as its wavelength, illumination profile and size are concern in this study. We made straightforward and quantitative comparisons among the effects by the light properties (i.e., wavelengths: 660, 810 and 980nm; beam types: Gaussian and flat beam; beam diameters: 0, 2, 4 and 6cm) which are in the range of light treatment. The findings include about 3% of light dosage within brain tissue; the combination of Gaussian beam and 810nm light make the maximum light penetration ($>5$cm), which allows light to cross through gray matter into white mater. This study offered us, the first time as we know, quantitative guide for light stimulation parameter optimization in medical treatment.

We discuss numerical investigations of the effects of cosmological inhomogeneities on light propagation. A new algorithm directly integrating the geodesics equations has been developed and has been run on very large scale cosmological simulations up to a redshift of z = 30. Comparisons have been made for several dark energy models and for several observers, revealing percent-level discrepancies between the angular diameter distance interpreted in a friedmannian background, and the angular diameter distance computed from geodesics integration. Here, we focus on the methodology that has been deployed to obtain quantitative results in cosmological simulations.

This contribution presents the analytical solution of the inverse ray tracing problem for photons emitted by a star and collected by an observer located in the gravitational field of the Solar System. This solution has been conceived to suit the accuracy achievable by the ESA Gaia satellite (launched on December 19, 2013) consistently with the measurement protocol in General Relativity adopted within the RAMOD framework. Aim of this study is to provide a general relativistic tool for the science exploitation of such a revolutionary mission, whose main goal is to trace back star directions from within our local curved space-time, therefore providing a three-dimensional map of our Galaxy. The calculations are performed assuming that the massive bodies of the Solar System move uniformly and have monopole and quadrupole structures. The results are useful for a thorough comparison and cross-checking validation of what already exists in the field of Relativistic Astrometry. Moreover, such an analytical solutions can be extended to model other measurements that require the same order of accuracy as that expected for Gaia.

Coherent control of light propagation in atomic and nuclear media is discussed. The main focus is on light propagation through so-called closed-loop media. We present a calculation technique which allows to evaluate and interpret the light propagation dynamics in closed-loop media. As an application, we discuss the realization of a so-called white-light cavity with artificially enhanced bandwidth. We further study light propagation in media which realize a cross-coupling of the electric and the magnetic probe field component. Finally, we discuss coherent control of nuclear forward scattering, as an example for light propagation in nuclear media.

While the radiosity method gradually established itself as a main rendering technique, there are still some fundamental problems regarding the radiosity method that remain unsolved. In this paper, we present a new radisosity approach for realistic image synthesis. Unlike the conventional radiosity method, the evaluation of light energy transfer is divided into two parts. In the first part, we establish the spatial light energy distribution of the source patch. In the second part, we subdivide the receiving surfaces accordingly and perform illumination calculation. The source patch and its receiving patches are related with each other through a global cube which acts as a light energy distributor. As no form—factors are involved, the conventional constraints on both the shooting patch and the receiving patch have been removed. Illumination coherence is exploited by performing dynamic subdivision of the receiving surface with respect to each current light source and by adaptive formation of the active light source. Accurate rendering of curved surfaces, anisotropic surfaces as well as the generation of high frequency details such as shadow edges, caustic borders and bump textures are supported efficiently. Experimental results show great potentials of the new approach.

The genesis of special relativity is intimately related to the development of the theory of light propagation. When optical phenomena were described, there are typically two kinds of theories: (i) One based on light rays and light particles and (ii) one considering the light as waves. When diffraction and refraction were experimentally discovered, light propagation became more often described in terms of waves. Nevertheless, when attempts were made to explain how light was propagated, it was nearly always in terms of a corpuscular theory combined with an ether, a subtle medium supporting the waves. Consequently, most of the theories from Newton’s to those developed in the 19th century were dual and required the existence of an ether. We therefore used the ether as our Ariadne thread for explaining how the principle of relativity became generalized to the so-called Maxwell equations around the 1900’s. Our aim is more to describe how the successive ideas were developed and interconnected than framing the context in which these ideas arose.