Li Xiao, Chen Jun, Lin Zhifang, Ng Jack
Department of Physics, Hong Kong Baptist University, Hong Kong, China.
Institute of Theoretical Physics and Collaborative Innovation Center of Extreme Optics, Shanxi University, Shanxi, China.
Sci Adv. 2019 Mar 29;5(3):eaau7814. doi: 10.1126/sciadv.aau7814. eCollection 2019 Mar.
Optical tractor beams, proposed in 2011 and experimentally demonstrated soon after, offer the ability to pull particles against light propagation. It has attracted much research and public interest. Yet, its limited microscopic-scale range severely restricts its applicability. The dilemma is that a long-range Bessel beam, the most accessible beam for optical traction, has a small half-cone angle, θ, making pulling difficult. Here, by simultaneously using several novel and compatible mechanisms, including transverse isotropy, Snell's law, antireflection coatings (or impedance-matched metamaterials), and light interference, we overcome this dilemma and achieve long-range optical pulling at θ ≈ 1°. The range is estimated to be 14 cm when using ~1 W of laser power. Thus, macroscopic optical pulling can be realized in a medium or in a vacuum, with good tolerance of the half-cone angle and the frequency of the light.
光学牵引光束于2011年被提出，随后不久便通过实验得到了验证，它能够使粒子逆着光的传播方向移动。这引起了大量的研究以及公众的兴趣。然而，其有限的微观尺度范围严重限制了它的适用性。困境在于，对于光学牵引而言最容易获得的光束——长程贝塞尔光束，其半锥角θ很小，使得牵引变得困难。在此，我们通过同时运用几种新颖且相互兼容的机制，包括横向各向同性、斯涅尔定律、抗反射涂层（或阻抗匹配超材料）以及光干涉，克服了这一困境，并在θ≈1°时实现了长程光学牵引。当使用约1W的激光功率时，该范围估计为14厘米。因此，可以在介质或真空中实现宏观光学牵引，并且对光的半锥角和频率具有良好的耐受性。
