Novel optical trapping geometries based on complex light fields

Valeria Bobkova, Westfälische Wilhelms-Universität Münster

Nowadays scientists go deeper and deeper trying to find out how the world around us functions and which forces play role on the basic interaction between atoms and molecules. Since objects of study became smaller researchers need an instrument to control and manipulate them. It is possible to trap tiny particles without touching them using light. It is also possible to investigate various properties of a small particles or even atoms and cooperation effects between them by observing their interaction with complex light fields.

Schematic of object sorting and trapping in complex engineered light fields

The main aim of the project is a comprehensive investigation of light-matter interaction and complex spatio-temporal optomechanical organization of colloidal suspensions, controlled by tailored light. The project includes on the one hand the design and fabrication of complex light structures as e.g. 3D orbital angular momentum (OAM)-carrying light fields for advanced optical trapping. We also realized a complex dynamic optical geometry based on Laguerre-Gaussian beams, which enables a “milling” scenario as proposed theoretically by the team of G.L. Oppo in the University of Strathclyde. It results in spatial particle sorting by size, which we applied to biomedical questions as e.g. sorting yeast cells from different sized silica spheres.

On the other hand, we investigate light-induced optomechanical self-organization of colloidal particles by combining the concept of single feedback with optical trapping by collective light-matter interaction and nonlinear coupling of a high number of these particles, leading to pattern formation within a colloidal suspension. It was shown in a number of nonlinear optical experiments that highly concentrated solutions of polystyrene beads with 100..200 nm diameters show nonlinear responses, namely self-focusing, four wave mixing and modulation instability were experimentally observed. Being influenced by the optical gradient force, particles are dragged in the direction of maximum intensity in the transversal plane, whereas the scattering force is compensated by the backward propagating beam. The density redistribution of the suspension in turn initiates a spatial modulation of the refractive index granting therefore the optical response.

Overall, we employ complex spatio-dynamically tailored light fields as well as self-organized pattern formation of light to create novel optical trapping schemes for dielectric nanoparticles as well as colloidal suspensions or biomedical cell cultures.

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ColOpt website poster_Bobkova