Gain-induced large optical torque in optical twist settings
Li Genyan1, 2, 3, Li Xiao4, Zhang Lei2, 3, 5, Chen Jun1, 2, 3, †
       

(a) A double-layer cluster made of a gain (ngain = 2 – 0.005i) and a lossy (nlossy = 2+0.005i) spheres with the separation between spheres D = 2a+0.002 μm. Optical torques for the upper gain (lossy) sphere and the lower lossy (gain) sphere are shown in panels (b) [(c)], respectively.