Tunable optical nonlinearity and self-collimation of light in food dye solutions

Food dyes are widely used in scientific research apart from the food colorant industry. In this work, we investigate nonlinear propagation of optical beams in food dye solutions of different colors, experimentally observing tunable nonlinearity and self-collimating effects of optical beams during propagation. We discuss possible mechanisms leading to optical nonlinearity by numerical simulation and theoretical analysis of the optical forces, and show that the nonlinearity in such solutions is mainly attributed to the thermo-optic effects. In addition, with appropriately mixed food dye solutions, we observe that nonlinear response arises at otherwise inactive wavelengths, leading to coupling of two self-collimated beams of different wavelengths. These results illustrate the possibility of employing low-cost food dye solutions for optical limiting and switching applications.