Light carries both linear momentum and angular momentum. The interactions between light and matter lead to momentum transfer/conversion that not only change the propagation of light but also induce forces on matter. These photon momentum effects can give rise to counterintuitive phenomena in artificial microstructures (i.e. man-made structures with desired properties). In this talk, I will discuss several phenomena that deepen our understanding of the fundamental properties of photon momentum. I will report that the light-induced force on a metamaterial boundary can be either pushing or pulling depending on the symmetry of microstructures [1,2]. I will also report that photonic spin-orbit interactions enabled by artificial microstructures can induce chirality-dependent lateral optical forces [3] and arbitrary-order non-Hermitian exceptional points [4]. Interpretations of these phenomena could help to resolve a century-old debate about photon momentum in media and generate novel applications such as ultra-sensitive optical sensors and sorting chiral molecules using light-induced forces.

References:

[1]   S. Wang, J. Ng, M. Xiao, and C. T. Chan, “Electromagnetic stress at the boundary: Photon pressure or tension?”, Science Advances 2, e1501485 (2016).

[2]   W. J. Sun, S. Wang, J. Ng, L. Zhou, and C. T. Chan, "Analytic derivation of electrostrictive tensors and their application to optical force density calculations", Physical Review B 91, 235439 (2015).

[3]   S. Wang and C. T. Chan, "Lateral optical force on chiral particles near a surface", Nature Communications 5, 3307 (2014).

[4]   S. Wang, B. Hou, W. Lu, Y. Chen, Z. Q. Zhang, and C. T. Chan, "Arbitrary order exceptional point induced by photonic spin-orbit interaction in coupled resonators", Nature Communications 10, 832 (2019).