细胞光阱刚度与折射率关系理论计算

Computation for Optical Trap Stiffness Versus Refractive Index of Biological Cell

为了探讨用光镊技术进行细胞折射率的测量方法,用几何光线理论对可作为米氏粒子模型的生物细胞（半径a=10μm,折射率n=1.35-1.70）,在单光束梯度力光阱[激光波长λ=780 nm,功率P=6 mW,焦斑半径w（0）=0.6μm、0.8μm和1.0μm]中的轴向光阱刚度与细胞折射率关系进行了数值计算。结果表明,光阱刚度随折射率的变化关系与三次多项式曲线拟合得较好;用测量光阱刚度计算细胞的折射率时,需要用折射率已知的四种标准粒子对三次多项式曲线进行标定。

In order to study the methods for measuring the refractive index of a biological cell based on optical tweezers technology, a ray-optics model has been used to predict the relationship between the trap stiffness and the refractive index of an ideal cell as a spherically symmetric Rayleigh sphere （radius a = 10 μm, refractive indices n = 1.35-1.70） in a single-beam gradient optical trapping （laser wavelength ;t= 780 nm, power P = 6 mW, beam waist radii ω（0）=0.6 μm, 0.8 μm and 1.0 μm）. Numerical simulation shows that the envelope of each curve is a cubic polynomial fitted well with the cell refractive indices. Results indicate that the calibration process for parameters of a cubic polynomial must be performed on four standard particles before the cell refractive index is obtained by measuring its trap stiffness.