光学捕获的非球形双折射粒子的取向
Orientation of optically trapped nonspherical birefringent particles
摘要：
虽然在光阱中的微粒的对准和旋转最近受到越来越多的关注，但最早的例子之一几乎完全忽略了粒子相对于光束轴的对准，而不是围绕光束轴。然而，由于对齐扭矩决定了粒子在阱中如何对齐，因此它们与实际应用直接相关。溶菌酶晶体是研究非球形双折射粒子在陷阱中取向的理想模型系统。它们的尺寸和纵横比都可以通过生长参数来控制，并且它们的规则形状使得计算建模变得可行。我们表明，外部形状和内部双折射各向异性有助于对齐扭矩。三维捕获的细长物体根据其尺寸与其长轴平行或垂直于光束轴对齐。形状相关的扭矩可以超过由于双折射引起的扭矩，并且可以使负单轴粒子与它们的光轴平行于电场对准，从而允许围绕光束轴施加光学扭矩。
英文摘要：
While the alignment and rotation of microparticles in optical traps have received increased attention recently, one of the earliest examples has been almost totally neglected the alignment of particles relative to the beam axis, as opposed to about the beam axis. However, since the alignment torques determine how particles align in a trap, they are directly relevant to practical applications. Lysozyme crystals are an ideal model system to study factors determining the orientation of nonspherical birefringent particles in a trap. Both their size and their aspect ratio can be controlled by the growth parameters, and their regular shape makes computational modeling feasible. We show that both external shape and internal birefringence anisotropy contribute to the alignment torque. Three-dimensionally trapped elongated objects either align with their long axis parallel or perpendicular to the beam axis depending on their size. The shape-dependent torque can exceed the torque due to birefringence, and can align negative uniaxial particles with their optic axis parallel to the electric field, allowing an application of optical torque about the beam axis.
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