Comment on: "Electromagnetically induced left-handedness in optically excited four-level atomic media"

We discuss the recent proposal by Thommen and Mandel (Phys. Rev. Lett. {\bf 96}, 053601 (2006)) for electromagnetically induced negative refraction. Although the main conclusion of the paper -- the possibility to achieve negative refraction in an experimentally accessible atomic scheme -- remains valid, we show that the weak-excitation approximation used is invalid in the parameter regime studied and leads to quantitatively incorrect predictions. We show that negative refraction is always accompanied by absorption rather than by gain, and that the maximum value of the refraction-absorption ratio is of order unity.Comment: 1 page, one figure, comment on Phys. Rev. Lett. {\bf 96}, 053601 (2006

Dmitrij Šostakovic (1906-1975) : Teil 1: die Jahre 1929-1940

Insgesamt für 34 Filme (wenige davon mit Fortsetzungen) schrieb Dmitrij Sostakovic begleitende Filmmusik. Er galt als guter Improvisator am Klavier, was ihm zu einer Arbeit im Kinotheater der Stummfilmzeit verhalf, die er benötigte, um seine Familie zu unterstützen und sein Studium am Petrograder Konservatorium zu finanzieren, wo er Klavier, Komposition und Kontrapunkt studierte

Antiviral immune responses in lumpfish (Cyclopterus lumpus) - with emphasis on type I interferons

Masteroppgave i molekylærbiologiMOL399MAMN-MO

Tunable negative refraction without absorption via electromagnetically induced chirality

We show that negative refraction with minimal absorption can be obtained by means of quantum interference effects similar to electromagnetically induced transparency. Coupling a magnetic dipole transition coherently with an electric dipole transition leads to electromagnetically induced chirality, which can provide negative refraction without requiring negative permeability, and also suppresses absorption. This technique allows negative refraction in the optical regime at densities where the magnetic susceptibility is still small and with refraction/absorption ratios that are orders of magnitude larger than those achievable previously. Furthermore, the value of the refractive index can be fine-tuned via external laser fields, which is essential for practical realization of sub-diffraction-limit imaging.Comment: 4 pages, 5 figures (shortened version, submitted to PRL

Van der Waals interaction and spontaneous decay of an excited atom in a superlens-type geometry

Within the framework of macroscopic quantum electrodynamics, the resonant van der Waals potential experienced by an excited two-level atom near a planar magneto-electric two-layer system consisting of a slab of left-handed material and a perfect mirror is studied. It is shown that disregarding of material absorption leads to unphysical results, with divergent values for the potential away from the surface. Under appropriate conditions, the setup is found to feature a barrier near the surface which can be employed to levitate particles or used as a trapping or cooling mechanism. Finally, the problem of spontaneous decay [J. K\"{a}stel and M. Fleischhauer, Phys. Rev. A \textbf{68}, 011804(R) (2005)] is revisited. Disregarding of absorption is shown to drastically falsify the dependence on the atomic position of the decay rate.Comment: 10 Pages, 6 figure

Low-Loss Negative Refraction by Laser Induced Magneto-Electric Cross-Coupling

We discuss the feasibility of negative refraction with reduced absorption in coherently driven atomic media. Coherent coupling of an electric and a magnetic dipole transition by laser fields induces magneto-electric cross-coupling and negative refraction at dipole densities which are considerably smaller than necessary to achieve a negative permeability. At the same time the absorption gets minimized due to destructive quantum interference and the ratio of negative refraction index to absorption becomes orders of magnitude larger than in systems without coherent cross-coupling. The proposed scheme allows for a fine-tuning of the refractive index. We derive a generalized expression for the impedance of a medium with magneto-electric cross coupling and show that impedance matching to vacuum can easily be achieved. Finally we discuss the tensorial properties of the medium response and derive expressions for the dependence of the refractive index on the propagation direction.Physic

Space debris removal by non-destructive orbit modification using ground-based high-power lasers

Accelerated deterioration of ecosystems naturally expands situational awareness from sustainability efforts towards emergency response. While this holds true for, e.g., climate change, the current evolution of Earth’s orbital environment develops into a status demanding for short-term action far beyond sustainability measures for space debris mitigation. Possibly not being the most relevant option for space sustainability efforts, high-power lasers might nonetheless play a significant role in response to the increasing number of known debris objects. Lasers, however, with a perception ranging from well-known everyday life applications via technology optimism and weaponization efforts up to visionary propulsion concepts, demand for a thoughtful assessment of their beneficial as well as their destructive potential regarding thermo-mechanical interaction with space debris. In our work we present a holistic approach to realistically assess conceivable contributions of ground-based highpower laser technology for mitigation of the space debris situation in the low Earth orbit. Departing from experimental work on laser-induced momentum coupling, our simulations cover aspects of beam transmission like atmospheric extinction, turbulence compensation, and beam pointing jitter. Laser-matter interaction is computed considering different generic target shapes, various target materials as well as the dependency of thermo-mechanical coupling on the incident laser fluence. Moreover, estimates are derived on the debris remediation performance of a repetitive 100 kJ laser system for perigee lowering to achieve atmospheric burnup after multiple laser station overpasses. The related laser irradiation constraints for operational safety are explored in terms of the target’s thermo-mechanical integrity throughout the entire orbit modification maneuver