We report a transverse optical torque exerted on a conventional isotropic spherical particle in a direction perpendicular to that of the illuminating wave propagation. By using full-wave simulations and deriving an analytical expression of the transverse optical torque for particle of arbitrary size, the origin of this transverse optical torque is traced exclusively to the magnetic part of the spin angular momentum, regardless of the size and composition of the illuminated particle. To our surprise, for a non-magnetic dielectric particle, the transverse optical torque is found to originate mainly from the magnetic response of the particle, even when the particle size is much smaller than the illuminating wavelength. This is contrary to the general intuition that the electric response of a non-magnetic dielectric particle dominates its magnetic response in the mechanical effect of light, especially in the Rayleigh limit.

中文翻译：

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来自磁自旋角动量的横向光扭矩


我们报告了在垂直于照明波传播方向的常规各向同性球形粒子上的横向光扭矩。通过使用全波模拟并推导出任意大小粒子的横向光矩的解析表达式，该横向光矩的来源完全追溯到自旋角动量的磁性部分，而不管被照亮粒子的大小和组成如何。令我们惊讶的是，对于非磁性介电粒子，即使粒子尺寸远小于照射波长，也发现横向光扭矩主要来自粒子的磁响应。这与一般的直觉相反，即非磁性介电粒子的电响应在光的机械效应中主导其磁响应，尤其是在瑞利极限下。