We report the implementation of a one-dimensional random laser based on an Er/Ge co-doped single-mode fiber with randomly spaced Bragg gratings. The random grating array forms a complex cavity with high quality factor resonances in the range of gain wavelengths centered around 1535.5 nm. The reflection spectra of the grating array and the emission spectra of the laser are investigated for different numbers of gratings. The experimental results are compared qualitatively with numerical simulations of the light propagation in one-dimensional Bragg grating arrays based on a transfer matrix method. The system is pumped at 980 nm and the experimentally observed output radiation presents a typical laser threshold behavior as a function of the pump power. We find that the laser output contains several competing spectral modes.

Perturbation theory is used to compute the angular-intensity correlation function C(q, k|q(?), k(?)) = ?[I(q|k) - ?I(q|k)?][I(q(?)|k(?)) - ?I(q(?)|k(?))]? for p-polarized light scattered from a weakly rough, one-dimensional random metal surface. I(q|k) is the squared modulus of the scattering matrix for the system, and q , q(?) and k , k(?) are the projections on the mean scattering surface of the wave vectors of the scattered and the incident light, respectively. Contributions to C include (a) short-range memory effect and time-reversed memory effect terms, C((1)) ; (b) an additional short-range term of comparable magnitude C((10)) ; (c) a long-range term C((2)) ; (d) an infinite-range term C((3)) ; and (e) a new term C((1.5)) that along with C((2)) displays peaks associated with the excitation of surface polaritons. These new features arise when the factorization approximation is not made in calculating the correlation function C .

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By a computer simulation approach we study the scattering of p-or s-polarized light from a twodimensional, randomly rough, perfectly conducting surface. The pair of coupled inhomogeneous integral equations for two independent tangential components of the magnetic field on the surface are converted into matrix equations by the method of moments, which are then solved by the biconjugate gradient stabilized method. The solutions are used to calculate the mean differential reflection coefficient for given angles of incidence and specified polarizations of the incident and scattered fields. The full angular distribution of the intensity of the scattered light is obtained for strongly randomly rough surfaces by a rigorous computer simulation approach.

In recent years it has been demonstrated both theoretically and experimentally that it is possible to cloak a predefined region of space from interaction with external volume electromagnetic waves, rendering an arbitrary object inside this region invisible to an outside observer. The several strategies that have been developed for achieving such cloaking cannot be applied directly to the cloaking of a surface feature from surface plasmon polaritons propagating on that surface. Here we demonstrate that it is possible to generate an arrangement of two concentric rings of point scatterers on a metal surface that significantly reduces the scattering of surface plasmon polaritons from an object enclosed within this circular structure.

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An accurate and efficient numerical simulation approach to electromagnetic wave scattering from two-dimensional, randomly rough, penetrable surfaces is presented. The use of the Müller equations and an impedance boundary condition for a two-dimensional rough surface yields a pair of coupled two-dimensional integral equations for the sources on the surface in terms of which the scattered field is expressed through the Franz formulas. By this approach, we calculate the full angular intensity distribution of the scattered field that is due to a finite incident beam of p-polarized light. We specifically check the energy conservation (unitarity) of our simulations (for the non-absorbing case). Only after a detailed numerical treatment of both diagonal and close-to-diagonal matrix elements is the unitarity condition found to be well-satisfied for the non-absorbing case (U > 0.995), a result that testifies to the accuracy of our approach. PACS numbers:The scattering of electromagnetic waves from twodimensional randomly rough penetrable surfaces has been studied theoretically for more than five decades. The methods used in these studies in recent years, where attention has been directed toward multiple-scattering phenomena, have been either analytical in nature or computational. Chief among the former methods has been the small-amplitude perturbation theory [1-3], while several different computational methods have been used in solving the scattering problem. In the earliest calculation of this type [4] the system of coupled inhomogeneous integral equations for the tangential components of the total electric and magnetic fields on the rough surface obtained from scattering theory, was converted into a system of inhomogeneous matrix equations by the use of the method of moments [5], which was then solved by Neumann-Liouville iteration [6]. This is a formally exact approach but one that is computationally (and memory) intensive.In subsequent work on this problem approximate solutions of the exact integral equations have been sought. In the sparse-matrix flat-surface iterative approach [7,8] the matrix elements for two close points on the surface are treated exactly, while those connecting two widely separated points are treated approximately, in an iterative solution of the matrix equations.Soriano and Saillard [9] have combined the sparsematrix flat-surface iterative approach with an impedance approximation [10] to calculate co-polarized and crosspolarized bistatic scattering coefficients of aluminum randomly rough surfaces for comparison with results obtained from perfectly conducting surfaces.An approach that combines the fast multipole method [11] and the sparse-matrix flat-surface iterative approach has been developed by Jandhyala et. al [12].Despite these advances, the calculation of the scattering of electromagnetic waves from two-dimensional, penetrable, randomly rough surfaces, remains a computationally intensive problem, in need of further improvements in the methods used to solve it.In this paper we use the Fran...

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