Spectrum of the volume integral operator of the three-dimensional electromagnetic scattering is analyzed. The operator has both continuous essential spectrum, which dominates at lower frequencies, and discrete eigenvalues, which spread out at higher ones. The explicit expression of the operator's symbol provides exact outline of the essential spectrum for any inhomogeneous anisotropic scatterer with Hölder continuous constitutive parameters. Geometrical bounds on the location of discrete eigenvalues are derived for various physical scenarios. Numerical experiments demonstrate good agreement between the predicted spectrum of the operator and the eigenvalues of its discretized version.
By placing, in vacuum, a stack of transmission dynodes (tynodes) on top of a CMOS pixel chip, a single free electron detector could be made with outstanding performance in terms of spatial and time resolution. The essential object is the tynode: an ultra thin membrane, which emits, at the impact of an energetic electron on one side, a multiple of electrons at the other side. The electron yields of tynodes have been calculated by means of GEANT-4 Monte Carlo simulations, applying special lowenergy extensions. The results are in line with another simulation based on a continuous charge-diffusion model. By means of Micro Electro Mechanical System (MEMS) technology, tynodes and test samples have been realised. The secondary electron yield of several samples has been measured in three different setups. Finally, several possibilities to improve the yield are presented.
We present a simple and unified classification of macroscopic electromagnetic resonances in finite arbitrarily inhomogeneous isotropic dielectric 3D structures situated in free space. By observing the complex-plane dynamics of the spatial spectrum of the volume integral operator as a function of angular frequency and constitutive parameters, we identify and generalize all the usual resonances, including complex plasmons, real laser resonances in media with gain, and real quasistatic resonances in media with negative permittivity and gain. DOI: 10.1103/PhysRevLett.96.023904 PACS numbers: 41.20.ÿq, 42.25.ÿp It is hard to overestimate the role played by macroscopic electromagnetic resonances in physics. Phenomena and technologies such as lasers, photonic band-gap materials, plasma waves and instabilities, microwave devices, and a great deal of electronics are all related or even entirely based on some kind of electromagnetic resonance. The usual way of analysis consists of deriving the so-called dispersion equation, which relates the wave vector k or the propagation constant jkj of a plane electromagnetic wave to the angular frequency !. The solutions of this equation may be real or complex. In the first case we talk about a real resonance, i.e., such that can be attained for some real angular frequency and therefore, in principle, results in unbounded fields. In reality, however, amplification of the fields is bounded by other physical mechanisms, e.g., nonlinear saturation. If the solution is complex, then we have a complex resonance and, depending on the sign of the imaginary part, the associated fields are either decaying or growing with time. This common approach is rather limited and does not include all pertaining phenomena. Indeed, more or less explicit dispersion equations can be obtained only for infinite (unbounded) homogeneous and periodic media, as often done in plasma and photonic studies. Other approaches impose explicit boundary conditions and can handle resonators and waveguides with perfectly conducting walls, and idealistic piecewise homogeneous objects (e.g., plane layered medium, circular cylinders, a sphere). On the other hand, very little can be said in the general case of a finite inhomogeneous dielectric object situated in free space. Because of the absence of an explicit dispersion equation and explicit boundary conditions, even the existence and classification of resonances in such objects is still an open problem.We describe here an alternative, mathematically rigorous approach to electromagnetic resonances, based on the volume integral formulation of the electromagnetic scattering, also known as the Green's function method and the domain integral equation method. This formulation is equivalent to the Maxwell's equations and is perfectly suited for bounded inhomogeneous objects in free space. Despite its generality, nowadays the volume integral equation is mostly used as a numerical tool, for instance, in near-field optics and geophysics. The main limitation seems to be the implicit ...
Since the 1983 definition of the speed of light in vacuum as a fundamental constant with the exact value of 299792458 m/s the question remains as to what apart from the wavefront travels at that speed. It is commonly assumed that the entire wave-packet or an impulse of the electromagnetic radiation in free space does. Here it is shown, both theoretically and experimentally, that there exists a region close to the source, where, while the wave-front travels at the speed of light, the individual impulses comprising the body of the wave-packet appear to slow down and even go backwards in time. This three-dimensional near-field late-time effect may also explain some of the free-space superluminal measurements.
Analytical solutions are presented for the electromagnetic radiation by an arbitrary pulsed source into a homogeneous time-varying background medium. In the constant-impedance case an explicit radiation formula is obtained for the synchronous permittivity and permeability described by any positive function of time. As might be expected, such a medium introduces significant spectral shifts and spatiotemporal modulation, which are analyzed here for the linear and exponential time variations of the medium parameters. In the varyingimpedance case the solution is obtained for the fourth-order polynomial time dependence of the permittivity. In addition to the spectral shifts and modulation this spatially homogeneous medium scatters the field introducing causal echoes at the receiver location.
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