Optical force-induced nonlinearity and self-guiding of light in human red blood cell suspensions

Abstract

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.

Optical spatial shock waves in nonlocal nonlinear media

“…The study of optical effects in light propagation through chemical and biological solutions is a field of growing interest [34,40,54,[86][87][88][89], both from a linear and a nonlinear perspective. However, although observations of nonlinear optical phenomena in chemical and soft-matter systems can be found in a large literature [27,30,32,33,36,38,46,54,[90][91][92][93], and new experiments in chemical media are useful only if the material owns very specific properties, little is known about nonlinearity in biological fluids and the related literature is very recent [40,88]. Bio-materials can be very interesting, because both chemical and biological compounds can be excellent tunable thermal media, and DSWs were already observed [27,34,40].…”

“…in M-Cresol/Nylon, a chemical solution that exhibits an isotropic giant self-defocusing nonlocal nonlinearity, tunable by varying the nylon concentration [34]. The second one in human red blood cell suspensions, where the concentration of hemoglobin (Hb) and the input laser beam power make the nonlinearity change from self-focusing to nonlocal defocusing [40]. Figure 12 shows transverse profiles of output beam intensity after a propagation of 2mm in M-Cresol/Nylon.…”

“…The input laser power was varied ranging from 2µW to 20mW and, when it reached 5mW, the wave-breaking occured. Figure 13 reports a part of the results obtained in lysed human red blood cells aged samples, where free Hb determines sign and nonlocality of the optical nonlinearity from self-focusing (and self-trapping) to strong thermal defocusing effects, regime in which DSWs occur [40]. Beyond the biological issues related to human red blood cells, holding uncountable applications to life sciences and medicine, red blood cells refractive index tunability makes this medium be incredibly interesting also from a physical point of view [94][95][96][97].…”

“…Dispersive shock waves (DSWs) are rapidly oscillating solutions of hyperbolic partial differential equations that contrast the generation of multivalued regions through the formation of undular bores [1][2][3][4][5][6][7][8][9][10][11]. This class of phenomena was investigated in several physical fields, initially in shallow water waves [12] and ion-acoustic waves [13], then in oceanography [14], pulses propagation in photonic fibers [15,16], Bose-Einstein condensates [17][18][19][20][21][22], quantum liquids [23], photorefractive media [24], plasma physics [25], viscous fluids [26], and diffracting optical beams [5,[27][28][29][30][31][32][33][34][35][36][37][38][39][40].…”

“…There, observations in Rhodamine with silica spheres [30] and in silica aerogel [33] exhibit the competition between randomness and nonlocal Kerr effect. DSW generation processes in chemical [34] and biological solutions [40] are illustrated in Sec. 3.3.…”