27 research outputs found
Axion-like-particle search with high-intensity lasers
We study ALP-photon-conversion within strong inhomogeneous electromagnetic
fields as provided by contemporary high-intensity laser systems. We observe
that probe photons traversing the focal spot of a superposition of Gaussian
beams of a single high-intensity laser at fundamental and frequency-doubled
mode can experience a frequency shift due to their intermittent propagation as
axion-like-particles. This process is strongly peaked for resonant masses on
the order of the involved laser frequencies. Purely laser-based experiments in
optical setups are sensitive to ALPs in the mass range and can
thus complement ALP searches at dipole magnets.Comment: 25 pages, 2 figure
There's No Place Like Home: Crown-of-Thorns Outbreaks in the Central Pacific Are Regionally Derived and Independent Events
One of the most significant biological disturbances on a tropical coral reef is a population outbreak of the fecund, corallivorous crown-of-thorns sea star, Acanthaster planci. Although the factors that trigger an initial outbreak may vary, successive outbreaks within and across regions are assumed to spread via the planktonic larvae released from a primary outbreak. This secondary outbreak hypothesis is predominantly based on the high dispersal potential of A. planci and the assertion that outbreak populations (a rogue subset of the larger population) are genetically more similar to each other than they are to low-density non-outbreak populations. Here we use molecular techniques to evaluate the spatial scale at which A. planci outbreaks can propagate via larval dispersal in the central Pacific Ocean by inferring the location and severity of gene flow restrictions from the analysis of mtDNA control region sequence (656 specimens, 17 non-outbreak and six outbreak locations, six archipelagos, and three regions). Substantial regional, archipelagic, and subarchipelagic-scale genetic structuring of A. planci populations indicate that larvae rarely realize their dispersal potential and outbreaks in the central Pacific do not spread across the expanses of open ocean. On a finer scale, genetic partitioning was detected within two of three islands with multiple sampling sites. The finest spatial structure was detected at Pearl & Hermes Atoll, between the lagoon and forereef habitats (<10 km). Despite using a genetic marker capable of revealing subtle partitioning, we found no evidence that outbreaks were a rogue genetic subset of a greater population. Overall, outbreaks that occur at similar times across population partitions are genetically independent and likely due to nutrient inputs and similar climatic and ecological conditions that conspire to fuel plankton blooms
Unified Homogenization Theory for Magnetoinductive and Electromagnetic Waves in Split Ring Metamaterials
A unified homogenization procedure for split ring metamaterials taking into
account time and spatial dispersion is introduced. The procedure is based on
two coupled systems of equations. The first one comes from an approximation of
the metamaterial as a cubic arrangement of coupled LC circuits, giving the
relation between currents and local magnetic field. The second equation comes
from macroscopic Maxwell equations, and gives the relation between the
macroscopic magnetic field and the average magnetization of the metamaterial.
It is shown that electromagnetic and magnetoinductive waves propagating in the
metamaterial are obtained from this analysis. Therefore, the proposed time and
spatially dispersive permeability accounts for the characterization of the
complete spectrum of waves of the metamaterial. Finally, it is shown that the
proposed theory is in good quantitative and qualitative agreement with full
wave simulations.Comment: 4 pages, 3 figure
Widespread intra-specific genetic homogeneity of coastal Antarctic benthic foraminifera
Tracing the phase of focused broadband laser pulses
Precise knowledge of the behaviour of the phase of light in a focused beam is
fundamental to understanding and controlling laser-driven processes. More than
a hundred years ago an axial phase anomaly for focused monochromatic light
beams was discovered and is now commonly known as the Gouy phase. Recent
theoretical work has brought into question the validity of applying this
monochromatic phase formulation to the broadband pulses becoming ubiquitous
today. Based on electron back-scattering at sharp nanometre-scale metal tips, a
method is available to measure light fields with sub-wavelength spatial
resolution and sub-optical cycle time resolution. Here we report such a direct,
three-dimensional measurement of the spatial dependence of the optical phase of
a focused, 4-fs, near-infrared laser pulse. The observed optical phase deviates
substantially from the monochromatic Gouy phase - exhibiting a much more
complex spatial dependence, both along the propagation axis and in the radial
direction. In our measurements, these significant deviations are the rule and
not the exception for focused, broadband laser pulses. Therefore, we expect
wide ramifications for all broadband laser-matter interactions, such as in
high-harmonic and attosecond pulse generation, femtochemistry, ophthalmological
optical coherence tomography and light-wave electronics.Comment: See journal reference for supplementary materia