A type of a random laser with a feedback organized by a number of randomly distributed fiber Bragg gratings (FBG) can demonstrate single-mode, or low threshold operation. Nevertheless, the spectrum of such lasers can be unstable. Here we study temporal variations of the spectra of random fiber laser with a set of Bragg gratings and show that they depend on the level of surrounding noise.
In this work, we report the experimental and numerical study of second harmonic generation (SHG) from Si-surface with randomly distributed Au-nanorods. The dependence of plasmonic resonance frequency was studied numerically for the gold nanorod-silicon dioxide-silicon substrate system as a function of nanorod sizes and dioxide film thickness. The numerical results demonstrate a high sensitivity of plasmonic resonance on the silicon dioxide thickness at the range up to 6 nm. We measured experimentally the dependencies of second harmonic signal as functions of the polarization angle of the pump beam from randomly distributed Au-nanorods on the Si-surface.
An approach to inverting experimental light scattering data for obtaining the normalized surface height autocorrelation function of a two-dimensional randomly rough dielectric surface, and its rms height is presented. It is based on the expression for the contribution to the mean differential reflection coefficient from the in-plane, co-polarized, light of s-polarization scattered diffusely from such a surface, obtained by phase perturbation theory. For weakly rough surfaces the reconstructions obtained by this approach are quite accurate.
This paper presents results of experimental and theoretical studies of light transmission through optical fibers with
disorder generated in its germanium-doped core via UV radiation transmitted through a diffuser. The experimental
results on transmission of the radiation of 543 nm wavelength demonstrate the presence of the disorder in the core
of the optical fiber - beyond a certain characteristic length, the transmitted power is observed to be distributed over
all modes of the fiber. A theoretical model based on coupled mode theory is developed. An analytical expression
for the mixing length is obtained and agrees well with the experiment. For long sections of disordered fiber, the
experimentally measured distribution of the near-field intensity at the output surface of the fiber is well described by
the Rayleigh negative exponential function. This suggests a statistically uniform distribution of the transmitted
power over all modes, that agrees with the prediction of the theoretical model. The reported technique provides an
easy way to fabricate different configurations of controlled disorder in optical fibers suitable for such applications
as random fiber lasers.
We present an experimental and theoretical investigation of the statistical properties of the light transmitted through a waveguide with a randomly rough section.
We present a new formulation of the self-energy and phase perturbation theories to calculate the reflectivities of randomly rough surfaces. The reflectivities calculated on the basis of our approach are compared with the results of rigorous numerical simulations of the problem and with the results of well controlled laboratory experiments.
We present an experimental and theoretical study of light scattering and propagation in multimode optical fibers with rough surfaces. In the experiments, performed at λ=655 nm, we used multimode 200 μm diameter silica glass fibers with an etched rough section. As the guided light reaches the rough part of the fiber it is scattered, feeding other modes and leaking out into the surrounding space. After some distance, however, the leakage decreases and the light within the fiber is carried primarily by the modes with low transverse wavenumbers. The light then propagates with a relatively narrow (half-width of about 0.15 rad) and slowly reducing angular spread. To understand this behavior, we develop a diffusion model for the intermode power transfer. The model predicts the formation of a narrow central maximum with a stable propagating angular profile, and relates parameters of the fiber and the surface roughness to the characterstic decay lengths.
In this work we present experimental and theoretical studies of the scattering of light propagating along a waveguide, a finite part of whose surface is randomly rough. We study the angular distribution of the intensity of the scattered light emerging from different parts of the rough surface. The angular distributions show a strong dependence on the distance of the radiating section from the front edge of the rough part of the waveguide. The experimental results are supported by theoretical studies of the problem. The angular distribution of the intensity of the light scattered into vacuum were calculated by means of a solution of the corresponding reduced Rayleigh equations.
We present an experimental study of the reflectivity of 2D randomly rough well-characterized, isotopic metallic surfaces. We proceed by comparing the experimental data with theoretical approaches of three perturbation theories and the Kirchhoff approximation. The samples were fabricated in photoresist, and their metallized surface profiles constitute good approximations to Gaussian-correlated, Gaussian random processes. The correlation lengths of these surfaces range form approximately one fifth to two times the IR wavelength employed.
An experimental investigation of the hemispherical distribution of the light scattered by randomly rough isotropic dielectric surfaces is presented. The surfaces, whose profiles constitute good approximations to Gaussian random processes with Gaussian correlation functions are fabricated in photoresist. The substrates employed in the fabrication of the samples consist of thick parallel plates of filter glass that absorb the incident light and whose refractive index is close to that of photoresist. This allows us to approximate experimentally a situation in which the light is scattered by a randomly rough interface separating two semi-infinite dielectric media. The results display features that can be attributed to multiple scattering. In particular, a well-defined enhanced backscattering peak is observed in both, the co- and cross-polarized scattering measurements.
An experimental investigation of the angular distribution of the light scattered by randomly rough, two-dimensional, isotropic dielectric surfaces is presented. The surfaces, whose profiles constitute good approximations to Gaussian random processes with Gaussian correlation functions are fabricated in photoresist and characterized by means of a mechanical profilometer. The substrates employed in the fabrication of the samples consist of thick parallel plates of filter glass that absorb the incident light and whose refractive index is close to that of photoresist. This allows us to approximate experimentally a situation in which the light is scattered by a randomly rough interface separating two semi-infinite dielectric media, illuminated from the air side. With the rougher surfaces, we have observed enhanced backscattering effects in both, the s and p cases of incident polarization. Small but important cross-polarized components of the scattered light have also been observed.
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