4,498 research outputs found
Statics and Dynamics of an Inhomogeneously-Nonlinear Lattice
We introduce an inhomogeneously-nonlinear Schr{\"o}dinger lattice, featuring
a defocusing segment, a focusing segment and a transitional interface between
the two. We illustrate that such inhomogeneous settings present vastly
different dynamical behavior than the one expected in their homogeneous
counterparts in the vicinity of the interface. We analyze the relevant
stationary states, as well as their stability by means of perturbation theory
and linear stability analysis. We find good agreement with the numerical
findings in the vicinity of the anti-continuum limit. For larger values of the
coupling, we follow the relevant branches numerically and show that they
terminate at values of the coupling strength which are larger for more extended
solutions. The dynamical development of relevant instabilities is also
monitored in the case of unstable solutions.Comment: 14 pages, 4 figure
Quadratic response theory for spin-orbit coupling in semiconductor heterostructures
This paper examines the properties of the self-energy operator in
lattice-matched semiconductor heterostructures, focusing on nonanalytic
behavior at small values of the crystal momentum, which gives rise to
long-range Coulomb potentials. A nonlinear response theory is developed for
nonlocal spin-dependent perturbing potentials. The ionic pseudopotential of the
heterostructure is treated as a perturbation of a bulk reference crystal, and
the self-energy is derived to second order in the perturbation. If spin-orbit
coupling is neglected outside the atomic cores, the problem can be analyzed as
if the perturbation were a local spin scalar, since the nonlocal spin-dependent
part of the pseudopotential merely renormalizes the results obtained from a
local perturbation. The spin-dependent terms in the self-energy therefore fall
into two classes: short-range potentials that are analytic in momentum space,
and long-range nonanalytic terms that arise from the screened Coulomb potential
multiplied by a spin-dependent vertex function. For an insulator at zero
temperature, it is shown that the electronic charge induced by a given
perturbation is exactly linearly proportional to the charge of the perturbing
potential. These results are used in a subsequent paper to develop a
first-principles effective-mass theory with generalized Rashba spin-orbit
coupling.Comment: 20 pages, no figures, RevTeX4; v2: final published versio
High power femtosecond source based on passively mode-locked 1055nm VECSEL and Yb-fibre power amplifier
We report 5 ns pulses at 160 W average power and 910 repetition rate from a passively mode-locked VECSEL source seeding an Yb-doped fibre power amplifier. The amplified pulses were compressed to 291 fs duration
Long-distance frequency transfer over an urban fiber link using optical phase stabilization
We transferred the frequency of an ultra-stable laser over 86 km of urban
fiber. The link is composed of two cascaded 43-km fibers connecting two
laboratories, LNE-SYRTE and LPL in Paris area. In an effort to realistically
demonstrate a link of 172 km without using spooled fiber extensions, we
implemented a recirculation loop to double the length of the urban fiber link.
The link is fed with a 1542-nm cavity stabilized fiber laser having a sub-Hz
linewidth. The fiber-induced phase noise is measured and cancelled with an all
fiber-based interferometer using commercial off the shelf pigtailed
telecommunication components. The compensated link shows an Allan deviation of
a few 10-16 at one second and a few 10-19 at 10,000 seconds
Long-distance remote comparison of ultrastable optical frequencies with 1e-15 instability in fractions of a second
We demonstrate a fully optical, long-distance remote comparison of
independent ultrastable optical frequencies reaching a short term stability
that is superior to any reported remote comparison of optical frequencies. We
use two ultrastable lasers, which are separated by a geographical distance of
more than 50 km, and compare them via a 73 km long phase-stabilized fiber in a
commercial telecommunication network. The remote characterization spans more
than one optical octave and reaches a fractional frequency instability between
the independent ultrastable laser systems of 3e-15 in 0.1 s. The achieved
performance at 100 ms represents an improvement by one order of magnitude to
any previously reported remote comparison of optical frequencies and enables
future remote dissemination of the stability of 100 mHz linewidth lasers within
seconds.Comment: 7 pages, 4 figure
First-principles envelope-function theory for lattice-matched semiconductor heterostructures
In this paper a multi-band envelope-function Hamiltonian for lattice-matched
semiconductor heterostructures is derived from first-principles norm-conserving
pseudopotentials. The theory is applicable to isovalent or heterovalent
heterostructures with macroscopically neutral interfaces and no spontaneous
bulk polarization. The key assumption -- proved in earlier numerical studies --
is that the heterostructure can be treated as a weak perturbation with respect
to some periodic reference crystal, with the nonlinear response small in
comparison to the linear response. Quadratic response theory is then used in
conjunction with k.p perturbation theory to develop a multi-band effective-mass
Hamiltonian (for slowly varying envelope functions) in which all interface
band-mixing effects are determined by the linear response. To within terms of
the same order as the position dependence of the effective mass, the quadratic
response contributes only a bulk band offset term and an interface dipole term,
both of which are diagonal in the effective-mass Hamiltonian. Long-range
multipole Coulomb fields arise in quantum wires or dots, but have no
qualitative effect in two-dimensional systems beyond a dipole contribution to
the band offsets.Comment: 25 pages, no figures, RevTeX4; v3: final published versio
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