Optical Funneling and Trapping of Gold Colloids in Convergent Laser Beams

The simultaneous trapping of a large number of sedimenting Au colloids by optical radiation forces has been studied in detail. The particles are collected by a convergent laser beam and compressed against gravity and osmotic pressure at the upper window of the cell, thereby forming a dense colloidal...

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Bibliographic Details
Published in:ACS nano 2012-05, Vol.6 (5), p.4400-4409
Main Authors: Koniger, Andreas, Kohler, Werner
Format: Article
Language:English
Subjects:
Clouds
Colloids
Gold
Laser beams
Lasers
Mathematical analysis
Mathematical models
Three dimensional
Trapping
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Summary:The simultaneous trapping of a large number of sedimenting Au colloids by optical radiation forces has been studied in detail. The particles are collected by a convergent laser beam and compressed against gravity and osmotic pressure at the upper window of the cell, thereby forming a dense colloidal gas. A minimum critical laser power is required to transport colloids into the trap. In contrast to conventional optical tweezers, the trap cannot be described by a 3D potential. Once the trap is sufficiently filled, the laser power can be reduced below the critical value, thereby stabilizing the trap population. Some characteristic properties of the trap, like the critical laser power and the transit time, are readily understood from a simple deterministic model. A detailed description that is capable of quantitatively accounting for the time dependence of the trap population, the finite leak rate at low power levels, or hysteresis effects requires the incorporation of fluctuations by means of a proper Langevin equation. Multiple independent traps are realized by time multiplexing of the laser beam, which allows for splitting up, independent manipulation, and subsequent recombination of a trapped colloidal cloud.
ISSN:1936-0851
1936-086X
DOI:10.1021/nn301080a