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BP: Fachverband Biologische Physik

BP 7: Posters I

BP 7.31: Poster

Monday, February 25, 2008, 17:00–19:30, Poster A

Linear and nonlinear laser-trapping microrheology — Daisuke Mizuno¹ and •Christoph F. Schmidt² — ¹Kyushu University, Fukuoka, Japan — ²Georg-August-Universität, Göttingen, Germany

We have developed a high-bandwidth technique for active 2-particle microrheology (AMR) with which we can probe linear and nonlinear responses of soft materials. Micron-sized colloidal probe particles are driven by an oscillating optical trap, and the resulting correlated motions of neighboring particles are detected by laser interferometry. Lock-in detection at the driving frequency and at its second harmonic makes it possible to measure the linear and the non-linear response of the embedding medium at the same time. We demonstrate the sensitivity of the method by detecting a second-harmonic response in water which is of purely geometric origin and which can be fully understood within linear hydrodynamics.