Soliton dynamics and self-induced transparency in nonlinear nanosuspensions

Abstract

We study spatial soliton dynamics in nano-particle suspensions. Starting from the Nernst-Planck and Smoluchowski equations, we demonstrate that in these systems the underlying nonlinearities as well as the nonlinear Rayleigh losses depend exponentially on optical intensity. Two different nonlinear regimes are identified depending on the refractive index contrast of the nanoparticles involved and the interesting prospect of self-induced transparency is demonstrated. Soliton stability is systematically analyzed for both 1D and 2D configurations and their propagation dynamics in the presence of Rayleigh losses is examined. The possibility of synthesizing artificial nonlinearities using mixtures of nanosuspensions is also considered.

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].…”

“…Like particles, the cells in a positive polarizability environment tend to be attracted against the diffusive Brownian motion towards the center of the light beam due to the optical gradient force [10,26,27]. This attraction leads to an increase in cell density along the beam path, which in turn creates an effective waveguide due to the higher index of the cyanobacteria compared to the host environment.…”

“…The particles are driven not only by an optical gradient force, but also by a scattering force in the forward direction, which is pivotal to the beam dynamics. The modified nonlinear Schrödinger equation used to simulate the beam propagation through the nonlinear medium can be written as [10,16] …”

“…Without the scattering force, the model reduces to the exponential nonlinearity in a steady state previously used to model dielectric nanosuspensions [10]. The model was solved numerically using a ð2 þ 1ÞD split-step algorithm that also included additional scattering effects modeled by random fluctuations of the refractive index.…”