1,254 research outputs found
Controlled lasing from active optomechanical resonators
Planar microcavities with distributed Bragg reflectors (DBRs) host, besides
confined optical modes, also mechanical resonances due to stop bands in the
phonon dispersion relation of the DBRs. These resonances have frequencies in
the sub-terahertz (10E10-10E11 Hz) range with quality factors exceeding 1000.
The interaction of photons and phonons in such optomechanical systems can be
drastically enhanced, opening a new route toward manipulation of light. Here we
implemented active semiconducting layers into the microcavity to obtain a
vertical-cavity surface-emitting laser (VCSEL). Thereby three resonant
excitations -photons, phonons, and electrons- can interact strongly with each
other providing control of the VCSEL laser emission: a picosecond strain pulse
injected into the VCSEL excites long-living mechanical resonances therein. As a
result, modulation of the lasing intensity at frequencies up to 40 GHz is
observed. From these findings prospective applications such as THz laser
control and stimulated phonon emission may emerge
Nuo Hans Gross iki lazerinio skenavimo – nusikaltimo vietos fiksavimo principai dabar ir tada
Hans Gross created with the first print of his book “Handbuch für Untersuchungsrichter,
Polizeibeamte, Gendarmen, usw.“ a standard volume for the
work at crime scenes in 1893. This book was published in several editions over
a time period of decades.
Throughout the time the technology, which is used for crime scene documentation,
has changed, correlated to the then actual available technology.
This article gives an overview about the changes in the technologies used at
crimes scenes for documentation between 1893 and 2022. It describes the way
from sketching and modelling to photography, Infrared-photography, spherical
panoramic photography and laser scanning. Many modern technologies are
based upon scientific principles which were described decades ago, although
people think, that they are new.
This article also takes a look upon what principles for the work at crime
scenes, postulated by Hans Gross, are still valid today
Observation of the transition from lasing driven by a bosonic to a fermionic reservoir in a GaAs quantum well microcavity
We show that by monitoring the free carrier reservoir in a GaAs-based quantum well microcavity under non-resonant pulsed optical pumping, lasing supported by a fermionic reservoir (photon lasing) can be distinguished from lasing supported by a reservoir of bosons (polariton lasing). Carrier densities are probed by measuring the photocurrent between lateral contacts deposited directly on the quantum wells of a microcavity that are partially exposed by wet chemical etching. We identify two clear thresholds in the input-output characteristic of the photoluminescence signal which can be attributed to polariton and photon lasing, respectively. The power dependence of the probed photocurrent shows a distinct kink at the threshold power for photon lasing due to increased radiative recombination of free carriers as stimulated emission into the cavity mode sets in. At the polariton lasing threshold on the other hand, the nonlinear increase of the luminescence is caused by stimulated scattering of exciton-polaritons to the ground state which do not contribute directly to the photocurrent.PostprintPeer reviewe
Rotating Hairy Black Holes
We construct stationary black holes in SU(2) Einstein-Yang-Mills theory,
which carry angular momentum and electric charge. Possessing non-trivial
non-abelian magnetic fields outside their regular event horizon, they represent
non-perturbative rotating hairy black holes.Comment: 13 pages, including 4 eps figures, LaTex forma
Prototype of a bistable polariton field-effect transistor switch
This work has been supported by the State of Bavaria.Microcavity exciton polaritons are promising candidates to build a new generation of highly nonlinear and integrated optoelectronic devices. Such devices range from novel coherent light emitters to reconfigurable potential landscapes for electrooptical polariton-lattice based quantum simulators as well as building blocks of optical logic architectures. Especially for the latter, the strongly interacting nature of the light-matter hybrid particles has been used to facilitate fast and efficient switching of light by light, something which is very hard to achieve with weakly interacting photons. We demonstrate here that polariton transistor switches can be fully integrated in electro-optical schemes by implementing a one-dimensional polariton channel which is operated by an electrical gate rather than by a control laser beam. The operation of the device, which is the polariton equivalent to a field-effect transistor, relies on combining electro-optical potential landscape engineering with local exciton ionization to control the scattering dynamics underneath the gate. We furthermore demonstrate that our device has a region of negative differential resistance and features a completely new way to create bistable behavior.Publisher PDFPeer reviewe
Pulsation of Spherically Symmetric Systems in General Relativity
The pulsation equations for spherically symmetric black hole and soliton
solutions are brought into a standard form. The formulae apply to a large class
of field theoretical matter models and can easily be worked out for specific
examples. The close relation to the energy principle in terms of the second
variation of the Schwarzschild mass is also established. The use of the general
expressions is illustrated for the Einstein-Yang-Mills and the Einstein-Skyrme
system.Comment: 21 pages, latex, no figure
Existence of spinning solitons in gauge field theory
We study the existence of classical soliton solutions with intrinsic angular
momentum in Yang-Mills-Higgs theory with a compact gauge group in
(3+1)-dimensional Minkowski space. We show that for \textit{symmetric} gauge
fields the Noether charges corresponding to \textit{rigid} spatial symmetries,
as the angular momentum, can be expressed in terms of \textit{surface}
integrals. Using this result, we demonstrate in the case of
the nonexistence of stationary and axially symmetric spinning excitations for
all known topological solitons in the one-soliton sector, that is, for 't
Hooft--Polyakov monopoles, Julia-Zee dyons, sphalerons, and also vortices.Comment: 21 pages, to appear in Phys.Rev.
Influence of Vitis xylem fluid and xylem fluid plus cecropin on growth of Xylella fastidiosa
Colony growth of Xylella fastidiosa (UCLA PD and STL PD strains) was quantified after incubation for 48 h in xylem fluid of Vitis rotundifolia Michx. cv. Noble and Vitis vinifera L. cv. Chardonnay. Xylem fluid was collected from grapevines in the field (dormant and growing season) and from container-grown plants in a screen house (growing season). Colony forming units·ml-1 (cfu·ml-1) were counted 15 d after plating on periwinkle wilt (PW+) medium. Colony growth was promoted or inhibited compared to PW+ medium, and was dependent on X. fastidiosa strain, plant species and source of xylem fluid. The efficacy of cecropin A and B was tested against this bacterium. Colony growth of X. fastidiosa was greatly inhibited after a 1-h-exposure to cecropin A or B. The minimum inhibitory concentration (MIC) of cecropin A or B for 100 % inhibition of X. fastidiosa was < 1 μM. The activity of cecropin B in xylem fluid of V. rotundifolia cv. Noble was progressively reduced over time from 0.2 to 24 h. When 2 and 10 μM concentrations of cecropin A and cecropin B were mixed with xylem fluid for 24 h, a substantial amount of bacterial growth occurred after subsequent plating; shorter time intervals did not degrade the cecropins and did not prevent colony growth. Cecropin B (1 μM) added to xylem fluid of V. rotundifolia cv. Noble and V. vinifera cv. Chardonnay for 24, 48, 72 and 96 h did not prevent subsequent colony growth. Colony number tended to be higher for V. rotundifolia cv. Noble than V. vinifera cv. Chardonnay. Tricine-sodium dodecyl sulphate polyacrylamide gel electrophoresis (Tricine-SDS-PAGE) of cecropin B in xylem fluid showed that cecropin B degraded completely (V. vinifera cv. Chardonnay) or almost completely (V. rotundifolia cv. Noble) after 96 h
On rotational excitations and axial deformations of BPS monopoles and Julia-Zee dyons
It is shown that Julia-Zee dyons do not admit slowly rotating excitations.
This is achieved by investigating the complete set of stationary excitations
which can give rise to non-vanishing angular momentum. The relevant zero modes
are parametrized in a gauge invariant way and analyzed by means of a harmonic
decomposition. Since general arguments show that the solutions to the
linearized Bogomol'nyi equations cannot contribute to the angular momentum, the
relevant modes are governed by a set of electric and a set of non self-dual
magnetic perturbation equations. The absence of axial dipole deformations is
also established.Comment: 22 pages, Revtex, no figure
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