2,168 research outputs found
Optimal frequency conversion in the nonlinear stage of modulation instability
We investigate multi-wave mixing associated with the strongly pump depleted
regime of induced modulation instability (MI) in optical fibers. For a complete
transfer of pump power into the sideband modes, we theoretically and
experimentally demonstrate that it is necessary to use a much lower seeding
modulation frequency than the peak MI gain value. Our analysis shows that a
record 95 % of the input pump power is frequency converted into the comb of
sidebands, in good quantitative agreement with analytical predictions based on
the simplest exact breather solution of the nonlinear Schr\"odinger equation
Nonautonomous Hamiltonians
We present a theory of resonances for a class of non-autonomous Hamiltonians
to treat the structural instability of spatially localized and time-periodic
solutions associated with an unperturbed autonomous Hamiltonian.
The mechanism of instability is radiative decay, due to resonant coupling of
the discrete modes to the continuum modes by the time-dependent perturbation.
This results in a slow transfer of energy from the discrete modes to the
continuum. The rate of decay of solutions is slow and hence the decaying bound
states can be viewed as metastable. The ideas are closely related to the
authors' work on (i) a time dependent approach to the instability of
eigenvalues embedded in the continuous spectra, and (ii) resonances, radiation
damping and instability in Hamiltonian nonlinear wave equations. The theory is
applied to a general class of Schr\"odinger equations. The phenomenon of
ionization may be viewed as a resonance problem of the type we consider and we
apply our theory to find the rate of ionization, spectral line shift and local
decay estimates for such Hamiltonians.Comment: To appear in Journal of Statistical Physic
Fundamentals and applications of spatial dissipative solitons in photonic devices : [Chapter 6]
We review the properties of optical spatial dissipative solitons (SDS). These are stable, self‐localized optical excitations sitting on a uniform, or quasi‐uniform, background in a dissipative environment like a nonlinear optical cavity. Indeed, in optics they are often termed “cavity solitons.” We discuss their dynamics and interactions in both ideal and imperfect systems, making comparison with experiments. SDS in lasers offer important advantages for applications. We review candidate schemes and the tremendous recent progress in semiconductor‐based cavity soliton lasers. We examine SDS in periodic structures, and we show how SDS can be quantitatively related to the locking of fronts. We conclude with an assessment of potential applications of SDS in photonics, arguing that best use of their particular features is made by exploiting their mobility, for example in all‐optical delay lines
Laser cooling and control of excitations in superfluid helium
Superfluidity is an emergent quantum phenomenon which arises due to strong
interactions between elementary excitations in liquid helium. These excitations
have been probed with great success using techniques such as neutron and light
scattering. However measurements to-date have been limited, quite generally, to
average properties of bulk superfluid or the driven response far out of thermal
equilibrium. Here, we use cavity optomechanics to probe the thermodynamics of
superfluid excitations in real-time. Furthermore, strong light-matter
interactions allow both laser cooling and amplification of the thermal motion.
This provides a new tool to understand and control the microscopic behaviour of
superfluids, including phonon-phonon interactions, quantised vortices and
two-dimensional quantum phenomena such as the Berezinskii-Kosterlitz-Thouless
transition. The third sound modes studied here also offer a pathway towards
quantum optomechanics with thin superfluid films, including femtogram effective
masses, high mechanical quality factors, strong phonon-phonon and phonon-vortex
interactions, and self-assembly into complex geometries with sub-nanometre
feature size.Comment: 6 pages, 4 figures. Supplementary information attache
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