236 research outputs found
Generation of unipolar half-cycle pulse via unusual reflection of a single-cycle pulse from an optically thin metallic or dielectric layer
We present a significantly different reflection process from an optically
thin flat metallic or dielectric layer and propose a strikingly simple method
to form approximately unipolar half-cycle optical pulses via reflection of a
single-cycle optical pulse. Unipolar pulses in reflection arise due to
specifics of effectively one-dimensional pulse propagation. Namely, we show
that in considered system the field emitted by a flat medium layer is
proportional to the velocity of oscillating medium charges instead of their
acceleration as it is usually the case. When the single-cycle pulse interacts
with linear optical medium, the oscillation velocity of medium charges can be
then forced to keep constant sign throughout the pulse duration. Our results
essentially differ from the direct mirror reflection and suggest a possibility
of unusual transformations of the few-cycle light pulses in linear optical
systems
Crossover from two-frequency pulse compounds to escaping solitons
The nonlinear interaction of copropagating optical solitons enables a large variety of intriguing bound-states of light. We here investigate the interaction dynamics of two initially superimposed fundamental solitons at distinctly different frequencies. Both pulses are located in distinct domains of anomalous dispersion, separated by an interjacent domain of normal dispersion, so that group velocity matching can be achieved despite a vast frequency gap. We demonstrate the existence of two regions with different dynamical behavior. For small velocity mismatch we observe a domain in which a single heteronuclear pulse compound is formed, which is distinct from the usual concept of soliton molecules. The binding mechanism is realized by the mutual cross phase modulation of the interacting pulses. For large velocity mismatch both pulses escape their mutual binding and move away from each other. The crossover phase between these two cases exhibits two localized states with different velocity, consisting of a strong trapping pulse and weak trapped pulse. We detail a simplified theoretical approach which accurately estimates the parameter range in which compound states are formed. This trapping-to-escape transition allows to study the limits of pulse-bonding as a fundamental phenomenon in nonlinear optics, opening up new perspectives for the all-optical manipulation of light by light
(Invited) Two-color soliton meta-atoms and molecules
We present a detailed overview of the physics of two-color soliton molecules in nonlinear waveguides, i.e. bound states of localized optical pulses which are held together due to an incoherent interaction mechanism. The mutual confinement, or trapping, of the subpulses, which leads to a stable propagation of the pulse compound, is enabled by the nonlinear Kerr effect. Special attention is paid to the description of the binding mechanism in terms of attractive potential wells, induced by the refractive index changes of the subpulses, exerted on one another through cross-phase modulation. Specifically, we discuss nonlinear-photonics meta atoms, given by pulse compounds consisting of a strong trapping pulse and a weak trapped pulse, for which trapped states of low intensity are determined by a Schrödinger-type eigenproblem. We discuss the rich dynamical behavior of such meta-atoms, demonstrating that an increase of the group-velocity mismatch of both subpulses leads to an ionization-like trapping-to-escape transition. We further demonstrate that if both constituent pulses are of similar amplitude, molecule-like bound-states are formed. We show that -periodic amplitude variations permit a coupling of these pulse compound to dispersive waves, resulting in the resonant emission of Kushi-comb-like multi-frequency radiation
Two-color soliton meta-atoms and molecules
We present a detailed overview of the physics of two-color soliton molecules
in nonlinear waveguides, i.e. bound states of localized optical pulses which
are held together due to an incoherent interaction mechanism. The mutual
confinement, or trapping, of the subpulses, which leads to a stable propagation
of the pulse compound, is enabled by the nonlinear Kerr effect. Special
attention is paid to the description of the binding mechanism in terms of
attractive potential wells, induced by the refractive index changes of the
subpulses, exerted on one another through cross-phase modulation. Specifically,
we discuss nonlinear-photonics meta atoms, given by pulse compounds consisting
of a strong trapping pulse and a weak trapped pulse, for which trapped states
of low intensity are determined by a Schr\"odinger-type eigenproblem. We
discuss the rich dynamical behavior of such meta-atoms, demonstrating that an
increase of the group-velocity mismatch of both subpulses leads to an
ionization-like trapping-to-escape transition. We further demonstrate that if
both constituent pulses are of similar amplitude, molecule-like bound-states
are formed. We show that z-periodic amplitude variations permit a coupling of
these pulse compound to dispersive waves, resulting in the resonant emission of
Kushi-comb-like multi-frequency radiation
All-optical attoclock: accessing exahertz dynamics of optical tunnelling through terahertz emission
The debate regarding attosecond dynamics of optical tunneling has so far been
focused on time delays associated with electron motion through the potential
barrier created by intense ionizing laser fields and the atomic core.
Compelling theoretical and experimental arguments have been put forward to
advocate the polar opposite views, confirming or refuting the presence of
tunnelling time delays. Yet, such delay, whether present or ot, is but a single
quantity characterizing the tunnelling wavepacket; the underlying dynamics are
richer. Here we propose to complement photo-electron detection with detecting
light, focusing on the so-called Brunel adiation -- the near-instantaneous
nonlinear optical response triggered by the tunnelling event. Using the
combination of single-color and two-color driving fields, we determine not only
the ionization delays, but also the re-shaping of the tunnelling wavepacket as
it emerges from the classically forbidden region. Our work introduces a new
type of attoclock for optical tunnelling, one that is based on measuring light
rather than photo-electrons. All-optical detection paves the way to
time-resolving multiphoton transitions across bandgaps in solids, on the
attosecond time-scale
Two-color pulse compounds in waveguides with a zero-nonlinearity point
We study incoherently coupled two-frequency pulse compounds in waveguides
with single zero-dispersion and zero-nonlinearity points. In such waveguides,
supported by a negative nonlinearity, soliton dynamics can be obtained even in
domains of normal dispersion. We demonstrate trapping of weak pulses by
solitary-wave wells, forming nonlinear-photonics meta-atoms, and molecule-like
bound-states of pulses. We study the impact of Raman effect on these pulse
compounds, finding that, depending on the precise subpulse configuration, they
decelerate, accelerate, or are completely unaffected. Our results extend the
range of systems in which two-frequency pulse compounds can be expected to
exist and demonstrate further unique and unexpected behavior
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