124 research outputs found
Quantum Hall Effect in Fractal Graphene: Growth and Properties of Graphlocons
Highly dendritic graphene crystals up to 0.25 mm in diameter are synthesized
by low pressure chemical vapor deposition inside a copper enclosure. With their
sixfold symmetry and fractal-like shape, the crystals resemble snowflakes. The
evolution of the dendritic growth features is investigated for different growth
conditions and surface diffusion is found to be the growth-limiting step
responsible for the formation of dendrites. The electronic properties of the
dendritic crystals are examined down to sub-Kelvin temperatures, showing a
mobility of up to 6300 cmVs and quantum Hall oscillations are
observed above 4T. These results demonstrate the high quality of the transport
properties despite their rough dendritic edges
Nonlinear mixing and mode correlations in a short Raman fiber laser
In the present paper we experimentally demonstrate a generation in a short Raman fiber laser having 10 000 different longitudinal modes only. We design the laser using 12 meters of commercially available fiber. Contrary to the recently demonstrated single longitudinal mode DFB Raman laser and short DBR Raman laser, in the laser under study the number of modes is high enough for efficient nonlinear interactions. Experimentally measured time dynamics reveals the presence of mode correlations in the radiation: the measured extreme events lasts for more than 10 round-trips
Modeling of the spectrum in a random distributed feedback fiber laser within the power balance modes
The simplest model for a description of the random distributed feedback (RDFB) Raman fiber laser is a power balance model describing the evolution of the intensities of the waves over the fiber length. The model predicts well the power performances of the RDFB fiber laser including the generation threshold, the output power and pump and generation wave intensity distributions along the fiber. In the present work, we extend the power balance model and modify equations in such a way that they describe now frequency dependent spectral power density instead of integral over the spectrum intensities. We calculate the generation spectrum by using the depleted pump wave longitudinal distribution derived from the conventional power balance model. We found the spectral balance model to be sufficient to account for the spectral narrowing in the RDFB laser above the threshold of the generation
Random distributed feedback fiber laser of ultimate efficiency
We demonstrate a random fiber laser of ultimate efficiency. More than 2 Watts are generated from 0.5W of pump excess over the generation threshold. At higher power, an optical efficiency corresponds to the quantum limit
Theory of nonlinear whispering gallery mode dynamics in a cylindrical microresonator with a radius variation
We propose a comprehensive model describing the Kerr nonlinear dynamics of an
electric field in a cylindrical microresonator with an effective radius
variation, coupled to a radiation source. The proposed system of equations for
coupled azimuthal modes takes into account full azimuthal dispersion as well as
the influence of the radiation source on the field in the microresonator with
the coupling coefficients determined experimentally. The model appears a
powerful tool to study nonlinear effects, generation axial-azimuthal modes and
optical frequency combs. We illustrate the power of the model with optimization
of the coupling point of the light source, getting two order of magnitude
improvement for the nonlinear threshold.Comment: 8 pages, 5 figure
Observation of localized modes at effective gauge field interface in synthetic mesh lattice
We predict a generic mechanism of wave localization at an interface between uniform artificial gauge fields, arising due to propagation-dependent phase accumulation similar to Aharonov-Bohm phenomenon. We realize experimentally a synthetic mesh lattice with real-time control over the vector gauge field, and observe robust localization under a broad variation of gauge strength and direction, as well as structural lattice parameters. This suggests new possibilities for confining and guiding waves in diverse physical systems through the synthetic gauge fields.This work was supported by the Russian Science Foundation (16-12-10402). A.A.S. acknowledges support by the
Australian Research Council (ARC) (DP160100619). I.D.V. acknowledges support of Ministry of Education and
Science of the Russian Federation (3.7672.2017/8.9)
Surface waves in mesh synthetic photonic lattices
Eigenmodes and dispersion curves in different configurations of synthetic photonic lattices are studied numerically. Eigenmodes localized on borders between areas with different optical potential are found. Stability of these eigenmodes against potential disturbances of different type is studied
Constructing eigenmode excitation spectrum in synthetic photonic lattices using optical heterodyning
A method based on optical heterodyning is proposed for measuring relative optical phases of pulses circulating in a synthetic photonic lattices. The knowledge of the phases can be further used for qualitative reconstruction of an eigenmode excitation spectrum in the synthetic photonic lattice
High-efficiency generation in a short random fiber laser
We demonstrate a high-efficiency random lasing in a 850 m span of a phosphosilicate fiber. Random distributed feedback owing to the Rayleigh backscattering in the fiber enables narrowband generation with output power of up to 7.3 W at the Stokes wavelength λS = 1308 nm from 11 Wof the pump power at λP = 1115 nm. The laser demonstrates unique generation efficiency. Near the generation threshold, more than 2 W of output power is generated from only 0.5 W of pump power excess over the generation threshold. At high pump power, the quantum conversion efficiency defined as a ratio of generated and pump photons at the laser output exceeds 100%. Itis explained by the fact that every pump photon is converted into the Stokes photon far from the output fiber end, while the Stokes photons have lower attenuation than the pump photons
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