Research On Rotation Characteristics Of Absorbing Particles Based On Δα-type Photopheresis

Optical trapping and manipulation of micro-sized and nano-sized particles with lasers has attracted extensive attention since the pioneering experiments of Ashkin and co-workers.Optical tweezers can be used to trap,stretch,cool,levitate,transport and rotate all kinds of particles.Due to micro motor has controlled movement performance,as a mobile platform,has been successfully used in drug transport,capture and sequester the cancer cells,DNA testing,Ion-Recognition,biochemical reagent degradation,oil processing and other aspects.Two themes in the biological medicine,environmental governance on the forefront of scientific problems has made outstanding achievements.Therefore,Light-induced rotation of objects trapped in optical tweezers has long been studied with great interest and it is essential.So far many mechanisms to generate the torque needed for the rotation were shown.In summary,two main basic classes have been proposed.In one,Light carrying the angular momentum itself interacts with the trapped particles to make them spin and plenty of possibilities were reported.The experimental apparatus of the first method is complex in structure,difficult in operation.In the other scheme,light with no angular momentum is scattered by an object in a helical manner.In this case the process is physically analogous to the rotation of a windmill:the torque of the rotation originates from the light deflected by the trapped particle.The second method makes it difficult to prepare rotors in light-induced rotation structures.In this paper,the method we proposed that trap and rotate light-absorbing particles by optical-fiber tweezers in the liquid is more convenient than that of using the traditional optical tweezers in structure and operation.The photophoretic forces caused by different thermal adaptation coefficients is used to trap and rotate the absorption micro particles in the liquid,and the motion mechanism caused by the photophoretic forces is analyzed.In addition,the performance of current light-induced micromotor devices is unsatisfactory,the conversion efficiency of the light-to-work is only 10^-15-10^-12.In this paper,we propose and demonstrate a laser-induced rotary micromotor operated byΔα-type photopheresis in the pure liquid glycerol,whose energy conversion ratio researches to as high as 10^-9,which is 3-6 orders of magnitude higher than previous light-induced micromotor devices.This article has done the following theoretical and experimental studies on the phenomenon of light-induced rotation based on the Δα-type photophoretic,which is mainly divided into the following works:First,the fiber probe with a section of annular-core fiber and a silica glass microsphere is configured.The output light field from the fiber probe is conical-shaped.And perform light-induced rotation on a graphite sheet.The torque of the light-induced rotation phenomenon is analyzed,and the force on this particle and torque expressions are deduced and simulated.Second,the fiber with the outer diameter and the inner diameter in order to fabricate the fiber probe with a different vertex angle is changed.The relationship between the vertex angle of the optical fiber probe and the light-induced rotation of the graphite sheet when the light vertex angles are 64°and 84°is studied respectively.The vertex angle of the fiber probe affects the relationship between the rotating rate and the incident laser power is concluded.The larger the vertex angle,the larger the maximum rotating rate.Finally,the relationship between the output power of the light source and the light-induced rotation speed of the graphite sheet by changing the output power of the light source is explored.In the experiment,the speed of the graphite microchip is 818.2 rpm when the light source output power is 14.9 m W.The conclusion that the speed of the light-induced rotation of graphite sheet increases with the output power of the light source is obtained.The energy conversion formula have been achieved,and its energy conversion rate is as high as10^-9.Light-induced micro motor has excellent in biological medicine and environmental application prospect.Using the light efficiently drive micro motor and programming tasks in the micro complex system is the ultimate goal of the micro motor.Light-induced rotation of absorbing microscopic particles by photophoretic forces in the liquid raises the possibility of optically driven micro machines.