Gain-induced large optical torque in optical twist settings

Li Genyan^{1, 2, 3}, Li Xiao⁴, Zhang Lei^{2, 3, 5}, Chen Jun^{1, 2, 3, †}

(a) The configuration of a double-layer cluster. (b) The structure of each layer in the double-layer cluster or a single layer. The separation between adjacent spheres is D = 2a+0.002 μm. Optical torques of the upper glass layer (n_glass = 1.33) and the lower gain layer (n_gain = 2 – 0.005i) in the gain–glass double-layer cluster are shown in panel (c), and the inset exhibits optical twist at resonances. Optical torques exerted on a single glass layer and that on the upper glass layer in a Ag–glass double-layer cluster are shown in panel (d) compared to the partial view of the black line in panel (c).