28 May 2002 Photoacoustic tweezers
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Proceedings Volume 4622, Optical Diagnostics of Living Cells V; (2002); doi: 10.1117/12.468341
Event: International Symposium on Biomedical Optics, 2002, San Jose, CA, United States
Abstract
The goal of this study was to develop a new approach to manipulating biological and nonbiological objects in liquid or gas, with a focus on living cells in liquid. This approach is based on laser-generated thermal and pressure gradients in the medium surrounding an object, which create forces of different origins acting on the object. In general, depending on the spatial geometry of these forces, particles can be trapped (symmetrical forces) or moved in desired directions (asymmetrical forces). Comparison of the different mechanisms for creating photothermal (PT) and photoacoustic (PA) gradients and their roles in manipulating particles are considered, including heating through absorption, optical breakdown, and plasma and bubble formation. The PA and PT gradients lead in turn to the formation of many physical phenomena, some of which may be important for particle movement, separation, sorting, and trapping. Among these phenomena are fast thermal expansion, acoustic radiation pressure, directed thermal convection, acoustic streamers, laser-induced jets, laser-generated high-frequency focused ultrasound, radiometric forces, nonisotropic Brownian motion, and asymmetry in thermal effects of irradiated particles, including thermal expansion, evaporation, ablation, and infrared (IR) radiation. Different phenomena are shown to play dominant roles in the manipulation of particles, depending on the particle or cell type, parameters of the surrounding medium, laser energy, and the beam's shape or geometry. The optical systems for particle manipulation using different laser spot shapes and geometry (i.e., circular, linear, crescent, or multispot and ring configurations) are presented. The advantages and limitations of this new member of the family of different 'tweezers' are discussed.
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Vladimir P. Zharov, "Photoacoustic tweezers", Proc. SPIE 4622, Optical Diagnostics of Living Cells V, (28 May 2002); doi: 10.1117/12.468341; https://doi.org/10.1117/12.468341
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KEYWORDS
Particles

Acoustics

Liquids

Optical tweezers

Pulsed laser operation

Absorption

Thermal effects

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