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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 16: Poster: Colloids and Complex Liquids

CPP 16.14: Poster

Dienstag, 27. März 2012, 18:15–20:45, Poster A

Optical trapping of gold colloids — •Andreas Königer and Werner Köhler — Physikalisches Institut, Universität Bayreuth

Using a strongly focused laser beam to trap and manipulate single colloidal particles is a well known procedure in life science and micro rheology. We have extended this technique using a convergent laser beam, with its focus well above a thin sample layer, to be able to manipulate many colloids simultaneously. Operating with an inverted microscope we have shown, how sedimented gold colloids can be lifted against gravity and collected in an almost 2-dimensional cage by radiation forces that act against the osmotic pressure of the compressed colloidal gas. Once collected, the cloud of colloids can be manipulated in a number of ways. It can freely be moved to arbitrary positions, where e.g. specific chemical reactions could take place. By time-multiplexing of the laser beam it is even possible to split the cloud into subensembles, which can than be manipulated independently and later be recombined by contact free purely optical means. We present a detailed analysis of the particle dynamics in the convergent light field and compare it to experimental data.