Spatial solitons and light-induced instabilities in colloidal media

Abstract

We study nonlinear light propagation in colloidal nanosuspensions. We introduce a novel model for the nonlinear response of colloids which describes consistently the system in the regimes of low and high light intensities and low/large concentrations of colloidal particles. We employ this model to study the light-induced instabilities and demonstrate the formation of stable spatial solitons as well as the existence of a bistability regime.

Nonlinear self-action of light through biological suspensions

“…Meanwhile, V represents the volume of an individual particle and n p its refractive index, n b stands for the refractive index of the background medium, and ρ denotes the intensity-dependent particle concentration. The spatial variation of ρ was, contrary to previous models [8][9][10][11][12][15][16][17]28], assumed to be driven not only by an optical gradient force but also by a scattering force in the forward direction of propagation. The temporal evolution of the particle concentration was modeled by a diffusionconvection equation,…”

“…Recently, there has been an increasing interest in light controlled motion of microorganisms and their hosting flows [6,7], but these controls are based on phototaxis in bacterial suspensions rather than optical nonlinearity. To efficiently propagate light through highly scattering media, it is important to study the nonlinear optical properties of soft-matter systems [8][9][10][11][12]. In particular, an optical nonlinearity can lead to stable low-loss propagation and deep penetration of light in scattering media such as nanoparticle suspensions, which could be employed to noninvasively initiate and control chemical or mesoscopic kinetic processes, as well as to study living organisms with high-resolution depth-resolved optical imaging [13,14].…”

Steering and guiding light with light in a nanosuspension

“…The main reason that permits these new observations is that the self-focused pump beam is allowed to propagate a considerably longer distance (at least one-order of magnitude longer) than previous experiments of the same kind [1,3,10]. It even exceeds distances reported in theoretical studies [7][8][9]. One especially relevant observation is the appearance of an annular structure around the main core of the self-trapped beam.…”

“…This fact renewed the interest on the subject and motivated the development of several theoretical models intended to elucidate the right kind of nonlinearity produced by the nanosuspensions. The general idea is to consider the medium as a gas of particles [6][7][8][9], where diffusion is driven by the optical gradient force until reaching equilibrium conditions. This leads to diverse expressions for the position-dependent particle density ρr, determined by the incident light spatial distribution and the characteristics of the nonlinear response of the medium.…”

“…(1). In order to explain the observation of stable propagation of OSS in 2 1D, different considerations and assumptions have been made, including for example, the presence of nonlinear Rayleigh losses [7], hard-sphere potential interactions [8], or screened Coulomb repulsions ("van der Waals" gas) [9], which lead to different kinds of nonlinearities, from Kerr to exponential. With the aim of testing the different theoretical approaches, new experiments were conducted recently [10].…”