76,526 research outputs found
Ultrafast and octave-spanning optical nonlinearities from strongly phase-mismatched cascaded interactions
Cascaded nonlinearities have attracted much interest, but ultrafast
applications have been seriously hampered by the simultaneous requirements of
being near phase-matching and having ultrafast femtosecond response times. Here
we show that in strongly phase-mismatched nonlinear frequency conversion
crystals the pump pulse can experience a large and extremely broadband
self-defocusing cascaded Kerr-like nonlinearity. The large cascaded
nonlinearity is ensured through interaction with the largest quadratic tensor
element in the crystal, and the strong phase-mismatch ensures an ultrafast
nonlinear response with an octave-spanning bandwidth. We verify this
experimentally by showing few-cycle soliton compression with noncritical
cascaded second-harmonic generation: Energetic 47 fs infrared pulses are
compressed in a just 1-mm long bulk lithium niobate crystal to 17 fs (under 4
optical cycles) with 80% efficiency, and upon further propagation an
octave-spanning supercontinuum is observed. Such ultrafast cascading is
expected to occur for a broad range of pump wavelengths spanning the near- and
mid-IR using standard nonlinear crystals.Comment: resubmitted, revised version, accepted for Phys. Rev. Let
Money, moral transgressions, and blame
Two experiments tested participants' attributions for others' immoral behaviors when conducted for more versus less money. We hypothesized and found that observers would blame wrongdoers more when seeing a transgression enacted for little rather than a lot of money, and that this would be evident in observers' hand-washing behavior. Experiment 1 used a cognitive dissonance paradigm. Participants (N = 160) observed a confederate lie in exchange for either a relatively large or a small monetary payment. Participants blamed the liar more in the small (versus large) money condition. Participants (N = 184) in Experiment 2 saw images of someone knocking over another to obtain a small, medium, or large monetary sum. In the small (versus large) money condition, participants blamed the perpetrator (money) more. Hence, participants assigned less blame to moral wrong-doers, if the latter enacted their deed to obtain relatively large sums of money. Small amounts of money accentuate the immorality of others' transgressions
Finite dimensional integrable Hamiltonian systems associated with DSI equation by Bargmann constraints
The Davey-Stewartson I equation is a typical integrable equation in 2+1
dimensions. Its Lax system being essentially in 1+1 dimensional form has been
found through nonlinearization from 2+1 dimensions to 1+1 dimensions. In the
present paper, this essentially 1+1 dimensional Lax system is further
nonlinearized into 1+0 dimensional Hamiltonian systems by taking the Bargmann
constraints. It is shown that the resulting 1+0 dimensional Hamiltonian systems
are completely integrable in Liouville sense by finding a full set of integrals
of motion and proving their functional independence.Comment: 10 pages, in LaTeX, to be published in J. Phys. Soc. Jpn. 70 (2001
Melt-growth dynamics in CdTe crystals
We use a new, quantum-mechanics-based bond-order potential (BOP) to reveal
melt-growth dynamics and fine-scale defect formation mechanisms in CdTe
crystals. Previous molecular dynamics simulations of semiconductors have shown
qualitatively incorrect behavior due to the lack of an interatomic potential
capable of predicting both crystalline growth and property trends of many
transitional structures encountered during the melt crystal
transformation. Here we demonstrate successful molecular dynamics simulations
of melt-growth in CdTe using a BOP that significantly improves over other
potentials on property trends of different phases. Our simulations result in a
detailed understanding of defect formation during the melt-growth process.
Equally important, we show that the new BOP enables defect formation mechanisms
to be studied at a scale level comparable to empirical molecular dynamics
simulation methods with a fidelity level approaching quantum-mechanical method
Finite-dimensional integrable systems associated with Davey-Stewartson I equation
For the Davey-Stewartson I equation, which is an integrable equation in 1+2
dimensions, we have already found its Lax pair in 1+1 dimensional form by
nonlinear constraints. This paper deals with the second nonlinearization of
this 1+1 dimensional system to get three 1+0 dimensional Hamiltonian systems
with a constraint of Neumann type. The full set of involutive conserved
integrals is obtained and their functional independence is proved. Therefore,
the Hamiltonian systems are completely integrable in Liouville sense. A
periodic solution of the Davey-Stewartson I equation is obtained by solving
these classical Hamiltonian systems as an example.Comment: 18 pages, LaTe
Dynamics of photoexcited carriers in graphene
The nonequilibrium dynamics of carriers and phonons in graphene is
investigated by solving the microscopic kinetic equations with the
carrier-phonon and carrier-carrier Coulomb scatterings explicitly included. The
Fermi distribution of hot carriers are found to be established within 100 fs
and the temperatures of electrons in the conduction and valence bands are very
close to each other, even when the excitation density and the equilibrium
density are comparable, thanks to the strong inter-band Coulomb scattering.
Moreover, the temporal evolutions of the differential transmission obtained
from our calculations agree with the experiments by Wang et al. [Appl. Phys.
Lett. 96, 081917 (2010)] and Hale et al. [Phys. Rev. B 83, 121404 (2011)] very
well, with two distinct differential transmission relaxations presented. We
show that the fast relaxation is due to the rapid carrier-phonon thermalization
and the slow one is mainly because of the slow decay of hot phonons. In
addition, it is found that the temperatures of the hot phonons in different
branches are different and the temperature of hot carriers can be even lower
than that of the hottest phonons. Finally, we show that the slow relaxation
rate exhibits a mild valley in the excitation density dependence and is
linearly dependent on the probe-photon energy.Comment: 9 pages, 4 figure
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