Laser-induced rotary micromotor with high energy conversion efficiency

Light is a precious resource that nature has given to human beings. Converting green, recyclable light energy into the mechanical energy of a micromotor is undoubtedly an exciting challenge. However, the performance of current light-induced micromotor devices is unsatisfactory, as the light-to-work conversion efficiency is only10-15–10-12. In this paper, we propose and demonstrate a laser-induced rotary micromotor operated byΔα-type photopheresis in pure liquid glycerol, whose energy conversion ratio reaches as high as 10-9, which is 3–6 orders of magnitude higher than that of previous light-induced micromotor devices. In addition, we operate the micromotor neither with a light field carrying angular momentum nor with a rotor with a special rotating symmetrical shape. We just employ an annular-core fiber to configure a conical-shaped light field and select a piece of graphite sheet （with an irregular shape） as the micro-rotor. TheΔα-type photophoretic force introduced by the conicalshaped light field drives the rotation of the graphite sheet. We achieve a rotation rate up to 818.2 r/min, which can be controlled by tuning the incident laser power. This optical rotary micromotor is available for twisting macromolecules or generating vortex and shear force in a medium at the nanoscale.