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A. A. Stahlhofen

Publications and source records attributed to A. A. Stahlhofen.

11 recordsLinked to original sources
arXiv2008

Resonance-like Goss-Haenchen Shift induced by nano-metal films

The influence of nano-metal films on the Goos-Haenchen shift (GHS) is investigated. The films deposited at the total reflecting surface of a perspex prism/air have a sheet resistance varying between Z = 25 and 3 000 Ohm. A resonance-like enhancement of the shift and of the absorption is found for TE polarized waves, when the sheet resistance approaches the value of the vacuum impedance. For TM waves the influence of the metal films on the GHS is comparatively weak. The experiments are carried out with microwaves. Keywords: Goos-Haenchen shift; nano-metallic films, microwaves PACS: 42.25.Bs, 42.25.Gy, 42.50.-p, 73.40.Gk

physics.optics↗
arXiv2008

How Long Is a Photon?

An interpretation of an electromagnetic quantum as a single pulse is suggested. In this context the Planck formula is shown to be equivalent to the Heisenberg time-energy uncertainty relation. This allows to treat the photon frequency as an inverse time of emission. Such an ansatz avoids the inherent problems of the conventional approach.

physics.gen-ph↗
arXiv2007

Comment on: Direct space-time observation of pulse tunneling in an electromagnetic band gap, S.Doiron,A.Hache,H.Winful

The title of this article is misleading. The authors have investigated a resonator but not a tunneling barrier see also Refs.\cite{Winful2} The measured superluminal group velocity and discussed is that studied on a Lorentz-Lorenz oscillator by Sommerfeld and Brillouin a hundred years ago \cite{Brillouin}. It is similar to the faster than light experiment by Wang et al. based also on anomalous dispersion with a complex refractive index of a resonator \cite{Wang}. Tunneling, however, is understood and performed by electromagnetic evanescent modes or by tunneling solutions of the Schrödinger equation, which have purely imaginary wave numbers. The latter includes a purely imaginary refractive index. Signals with purely evanescent frequency components can travel at a superluminal velocity \cite{NimtzH,Nimtz1}. Inside the barrier tunneling proceeds even instantaneously, i.e.by a process described by virtual photons \cite{Stahlhofen}.

quant-ph↗
arXiv2007

Universal tunneling time for all fields

Tunneling is an important physical process. The observation that particles surmount a high mountain in spite of the fact that they don't have the necessary energy cannot be explained by classical physics. However, this so called tunneling became allowed by quantum mechanics. Experimental tunneling studies with different photonic barriers from microwave frequencies up to ultraviolet frequencies pointed towards a universal tunneling time (Haibel,Esposito). Experiments and calculations have shown that the tunneling time of opaque photonic barriers (optical mirrors, e.g.) equals approximately the reciprocal frequency of the corresponding electromagnetic wave. The tunneling process is described by virtual photons. Virtual particles like photons or electrons are not observable. However, from the theoretical point of view, they represent necessary intermediate states between observable real states. In the case of tunneling there is a virtual particle between the incident and the transmitted particle. Tunneling modes have a purely imaginary wave number. They represent solutions of the Schroedinger equation and of the classical Helmholtz equation. Recent experimental and theoretical data of electron and sound tunneling confirmed the conjecture that the tunneling process is characterized by a universal tunneling time independent of the kind of field. Tunneling proceeds at a time of the order of the reciprocal frequency of the wave.

quant-ph↗
arXiv2007

Macroscopic violation of special relativity

Feynman one of the founders of Quantum Electronic Dynamics (QED) introduced in his diagrams virtual particles as intermediate states of an interaction process. Such virtual particles are not observable, however, from the theoretical point of view they represent necessary intermediate states between observable real states. Such virtual particles were introduced for describing the interaction process between an electron and a positron and for much more complicated interaction processes. Other candidates for virtual photons are evanescent modes known from optics. Evanescent modes have a purely imaginary wave number, they represent the mathematical analogy of the tunneling solutions of the Schrödinger equation. Evanescent modes are present in the optical processes of total reflection and in undersized wave guides for instance. The most prominent example of the occurrence of evanescent modes is frustrated total internal reflection at double prisms. In 1949 Sommerfeld \cite{Sommerfeld} pointed out that this optical phenomenon represents the analogy of quantum mechanical tunneling. The evanescent modes and tunneling violate the theory of special relativity, obviously, they represent the exception which proves the special theory of relativity. We demonstrate the quantum mechanical behavior of evanescent modes \textbf{with digital microwave} signals at a macroscopic scale of the order of a meter and show that evanescent modes are well described by virtual photons as predicted by former QED calculations.

quant-ph↗
arXiv2007

Local Energy Velocity of Classical Fields

It is proposed to apply a recently developed concept of local wave velocities to the dynamical field characteristics, especially for the canonical field energy density. It is shown that local energy velocities can be derived from the lagrangian directly. The local velocities of zero- and first- order for energy propagation has been obtained for special cases of scalar and vector fields. Some important special cases of these results are discussed.

physics.gen-ph↗
arXiv2007

A Local Concept of Wave Velocities

The classical characterization of \wp, as a typical concept for far field phenomena, has been successfully applied to many \w phenomena in past decades. The recent reports of superluminal tunnelling times and negative group velocities challenged this concept. A new local approach for the definition of \wvs avoiding these difficulties while including the classical definitions as particular cases is proposed here. This generalisation of the conventional non-local approach can be applied to arbitrary \w forms and propagation media. Some applications of the formalism are presented and basic properties of the concept are summarized.

math-ph↗
arXiv2006

On a Local Concept of Wave Velocities

The classical far field concept of wave velocities has its merits while exibiting intrinsic difficulties. A general local approach for the definition of velocities and especially phase velocities for waves avoiding these difficulties is proposed. It includes the classical definitions as particular cases and can be applied to waves of an arbitrary structure, and to arbitrary propagation media as well. Applications of the formalism are elucidated and some basic properties of the local concept defined here are discussed.

math-ph↗
arXiv2000

From Superluminal Velocity To Time Machines?

Various experiments have shown superluminal group and signal velocities recently. Experiments were essentials carried out with microwave tunnelling, with frustrated total internal reflection, and with gain-assisted anomalous dispersion. According to text books a superluminal signal velocity violates Einstein causality implying that cause and effect can be changed and time machines known from science fiction could be constructed. This naive analysis, however, assumes a signal to be a point in the time dimension neglecting its finite duration. A signal is not presented by a point nor by its front, but by its total length. On the other hand a signal energy is finite thus its frequency band is limited, the latter is a fundamental physical property in consequence of field quantization with quantum $h ν$. All superluminal experiments have been carried out with rather narrow frequency bands. The narrow band width is a condition sine qua non to avoid pulse reshaping of the signal due to the dispersion relation of the tunnelling barrier or of the excited gas, respectively. In consequence of the narrow frequency band width the time duration of the signal is long so that causality is preserved. However, superluminal signal velocity shortens the otherwise luminal time span between cause and effect.

physics.class-ph↗