期刊
MACROMOLECULAR RESEARCH
卷 25, 期 3, 页码 282-289出版社
SPRINGER
DOI: 10.1007/s13233-017-5027-7
关键词
polymer microsphere; optical trap; colloid; drag calibration; ray optics approximation
资金
- Kyung Hee University [KHU-20141582]
- Engineering Research Center of Excellence Program of the Korea Ministry of Science, ICT & Future Planning (MSIP)/National Research Foundation of Korea [NRF-2014R1A5A1009799]
We present analytical calculations of optical forces for drag calibrations via the geometrical optics approximation (GOA) for the case in which a single laser beam is strongly focused on a polystyrene microsphere dispersed in an aqueous phase. When the beam focus is mismatched with the particle center owing to the presence of vertical forces, such as gravity, buoyancy, and the radiation force caused by the laser beam, the trapped particle would be displaced in a radial direction when the lateral drag force is applied. Based on the analytical calculations of optical trapping forces and the force balance upon dragging, we found that the critical laser power at which the beam focus matches the particle center exhibits a power-law relationship with the particle radius a according to the empirical expression log( P-crit ( mW)) = 2.899 log(2a (mu m)) - 2.316. We also found an empirical expression for the mechanical equilibrium position of the vertical displacement Delta z(eq)(0)(Delta y= 0) as functions of the laser power P and the particle radius,Delta z(eq)(0) =[F(gb)pN)-0.068p(mW)][2.7(mu m)-0.052]/p(mW),where F-gb is the sum of the gravitational and buoyant forces.
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