706 research outputs found
Novel fabrication technique for planar glass waveguides
A novel technique has been developed for the deposition of low-loss planar glass waveguides by directly spin coating from the liquid, thus overcoming the problems of reproducing glass stoichiometry when depositing from the vapour
On Bogovski\u{\i} and regularized Poincar\'e integral operators for de Rham complexes on Lipschitz domains
We study integral operators related to a regularized version of the classical
Poincar\'e path integral and the adjoint class generalizing Bogovski\u{\i}'s
integral operator, acting on differential forms in . We prove that these
operators are pseudodifferential operators of order -1. The Poincar\'e-type
operators map polynomials to polynomials and can have applications in finite
element analysis. For a domain starlike with respect to a ball, the special
support properties of the operators imply regularity for the de Rham complex
without boundary conditions (using Poincar\'e-type operators) and with full
Dirichlet boundary conditions (using Bogovski\u{\i}-type operators). For
bounded Lipschitz domains, the same regularity results hold, and in addition we
show that the cohomology spaces can always be represented by
functions.Comment: 23 page
Correlated electron emission in laser-induced nonsequence double ionization of Helium
In this paper, we have investigated the correlated electron emission of the
nonsequence double ionization (NSDI) in an intense linearly polarized field.
The theoretical model we employed is the semiclassical rescattering model, the
model atom we used is the helium. We find a significant correlation between
magnitude and direction of the momentum of two emission electrons, and give a
good explanation for this striking phenomenon by observing the classical
collisional trajectories. We argue that this correlation phenomenon is
universal in NSDI process, as revealed by the recent experiment on the argon.Comment: 4 pages, 3 figures, accepted for publication in Phys. Rev.
Magnetically Stabilized Luminescent Excitations in Hexagonal Boron Nitride
Magnetically stabilized luminescence is observed in hexagonal boron nitride.
The luminescence is induced by absorption of cold neutrons and is in the
visible region. In the absence of a magnetic field, the photon emission level
is observed to decay over several hundred seconds. A fraction of this
luminescence can be suppressed if the temperature is T <~ 0.6 K and the
magnetic field is B >~ 1.0 T. Subsequent to irradiation and suppression,
luminescence can be induced by an increase in T or lowering of B. Possible
explanations include stabilization of triplet states or the localization and
stabilization of excitons.Comment: 11 pages, 7 figures, to appear in the Journal of Luminescenc
Scintillation and charge extraction from the tracks of energetic electrons in superfluid helium-4
An energetic electron passing through liquid helium causes ionization along
its track. The ionized electrons quickly recombine with the resulting positive
ions, which leads to the production of prompt scintillation light. By applying
appropriate electric fields, some of the ionized electrons can be separated
from their parent ions. The fraction of the ionized electrons extracted in a
given applied field depends on the separation distance between the electrons
and the ions. We report the determination of the mean electron-ion separation
distance for charge pairs produced along the tracks of beta particles in
superfluid helium at 1.5 K by studying the quenching of the scintillation light
under applied electric fields. Knowledge of this mean separation parameter will
aid in the design of particle detectors that use superfluid helium as a target
material.Comment: 10 pages, 8 figure
Nuttier Bubbles
We construct new explicit solutions of general relativity from double
analytic continuations of Taub-NUT spacetimes. This generalizes previous
studies of 4-dimensional nutty bubbles. One 5-dimensional locally
asymptotically AdS solution in particular has a special conformal boundary
structure of . We compute its boundary stress tensor and
relate it to the properties of the dual field theory. Interestingly enough, we
also find consistent 6-dimensional bubble solutions that have only one timelike
direction. The existence of such spacetimes with non-trivial topology is
closely related to the existence of the Taub-NUT(-AdS) solutions with more than
one NUT charge. Finally, we begin an investigation of generating new solutions
from Taub-NUT spacetimes and nuttier bubbles. Using the so-called Hopf duality,
we provide new explicit time-dependent backgrounds in six dimensions.Comment: 32 pages, 1 figure; v.3. typos corrected. Matches the published
versio
Acousto-optically Q-switched fibre laser source of high peak power and short duration pulses for fibre sensor applications
We report on a fibre laser source which emits high peak power (>0.7 kW) and short (2.8 ns) Q-switched pulses at 1.06 µm suitable for distributed fibre sensor applications using an absorbed pump power of 13 mW and miniature acousto-optic modulator
Creating diamond color centers for quantum optical applications
Nitrogen vacancy (NV) centers in diamond have distinct promise as solid-state
qubits. This is because of their large dipole moment, convenient level
structure and very long room-temperature coherence times. In general, a
combination of ion irradiation and subsequent annealing is used to create the
centers, however for the rigorous demands of quantum computing all processes
need to be optimized, and decoherence due to the residual damage caused by the
implantation process itself must be mitigated. To that end we have studied
photoluminescence (PL) from NV, NV and GR1 centers formed by ion
implantation of 2MeV He ions over a wide range of fluences. The sample was
annealed at C to minimize residual vacancy diffusion, allowing for
the concurrent analysis of PL from NV centers and irradiation induced vacancies
(GR1). We find non-monotic PL intensities with increasing ion fluence,
monotonic increasing PL in NV/NV and GR1/(NV + NV) ratios, and
increasing inhomogeneous broadening of the zero-phonon lines with increasing
ion fluence. All these results shed important light on the optimal formation
conditions for NV qubits. We apply our findings to an off-resonant photonic
quantum memory scheme using vibronic sidebands
Emergent Gravity from Noncommutative Gauge Theory
We show that the matrix-model action for noncommutative U(n) gauge theory
actually describes SU(n) gauge theory coupled to gravity. This is elaborated in
the 4-dimensional case. The SU(n) gauge fields as well as additional scalar
fields couple to an effective metric G_{ab}, which is determined by a dynamical
Poisson structure. The emergent gravity is intimately related to
noncommutativity, encoding those degrees of freedom which are usually
interpreted as U(1) gauge fields. This leads to a class of metrics which
contains the physical degrees of freedom of gravitational waves, and allows to
recover e.g. the Newtonian limit with arbitrary mass distribution. It also
suggests a consistent picture of UV/IR mixing in terms of an induced gravity
action. This should provide a suitable framework for quantizing gravity.Comment: 28 pages + 11 pages appendix. V2: references and discussion added.
V3: minor correctio
A diode-laser-pumped, Er<sup>3+</sup>-doped fibre laser operating at 1.57µm
Erbium-doped fibers show promise as stable narrow-linewidth laser sources and optical amplifiers operating in the third telecommunications window around 1.55µm Diode laser pumping is possible using the weak pump-band located at 807nm, although this band suffers severely from excited-state absorption (ESA), which reduces gain and pump efficiency. At the low pump power available from diode lasers the Er3+ behaves as a quasi four-level system. However, by codoping the core glass heavily with Yb3+, it is possible to excite the Er3+ ions indirectly using energy transfer. The Yb3+ provides an intense broad pump-band centered at 900nm, which reduces the effect of ESA. As a consequence of the resulting higher pump efficiency, the laser will oscillate at the required shorter wavelengths
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