The optical spatial solitons with ellipse-shaped spots have generally been considered to be a result of either linear or nonlinear anisotropy. In this paper, we introduce a class of spiraling elliptic solitons in the nonlocal nonlinear media without both linear and nonlinear anisotropy. The spiraling elliptic solitons carry the orbital angular momentum, which plays a key role in the formation of such solitons, and are stable for any degree of nonlocality except the local case when the response function of the material is Gaussian function. The formation of such solitons can be attributable to the effective anisotropic diffraction (linear anisotropy) resulting from the orbital angular momentum. Our variational analytical result is confirmed by direct numerical simulation of the nonlocal nonlinear Schrödinger equation.
Osmotic conditions play an important role in the cell properties of human red blood cells (RBCs), which are crucial for the pathological analysis of some blood diseases such as malaria. Over the past decades, numerous efforts have mainly focused on the study of the RBC biomechanical properties that arise from the unique deformability of erythrocytes. Here, we demonstrate nonlinear optical effects from human RBCs suspended in different osmotic solutions. Specifically, we observe self-trapping and scattering-resistant nonlinear propagation of a laser beam through RBC suspensions under all three osmotic conditions, where the strength of the optical nonlinearity increases with osmotic pressure on the cells. This tunable nonlinearity is attributed to optical forces, particularly the forward-scattering and gradient forces. Interestingly, in aged blood samples (with lysed cells), a notably different nonlinear behavior is observed due to the presence of free hemoglobin. We use a theoretical model with an optical force-mediated nonlocal nonlinearity to explain the experimental observations. Our work on light self-guiding through scattering bio-soft-matter may introduce new photonic tools for noninvasive biomedical imaging and medical diagnosis.
It is demonstrated that the orbital angular momentum (OAM) carried by the elliptic beam without the phase-singularity can induce the anisotropic diffraction (AD). The quantitative relation between the OAM and its induced AD is analytically obtained by a comparison of two different kinds of (1+2)-dimensional beam propagations: the linear propagations of the elliptic beam without the OAM in an anisotropic medium and that with the OAM in an isotropic one. In the former case, the optical beam evolves as the fundamental mode of the eigenmodes when its ellipticity is the square root of the anisotropic parameter defined in the paper; while in the latter case, the fundamental mode exists only when the OAM carried by the optical beam equals a specific one called a critical OAM. The OAM always enhances the beam-expanding in the major-axis direction and weakens that in the minor-axis direction no matter the sign of the OAM, and the larger the OAM, the stronger the AD induced by it. Besides, the OAM can also make the elliptic beam rotate, and the absolute value of the rotation angle is no larger than π/2 during the propagation.
In nonlocal nonlinear media with a sine-oscillation response function, two kinds of spatial solitons with complicated structure, in-phase and out-of-phase bound-state solitons, are obtained numerically in the case of the weak nonlocality. The in-phase bound-state soliton exhibits the symmetrical profile and the nonzero central value, and the out-of-phase bound-state soliton has the antisymmetrical profile and the zero central value. The two kinds of bound-state solitons form the degenerate modes subject to the same dependance of soliton power on the propagation constant. For those solitons there exist two abnormal properties: both the soliton propagation constants and the slope of the power versus propagation constants are negative. Both the in-phase and the out-of-phase bound-state solitons are stable by the linear stability analysis, and the stability of the two kinds of solitons obey an inverted Vakhitov-Kolokolov stability criterion. We also discuss the way how to obtain a set of the soliton solutions from one numerical soliton solution via the transform invariance of the nonlocal nonlinear Schrödinger equation and the nonlinear Schrödinger equation.
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