Artistic representation of a microdrone with two active light-driven nanomotors between red cell. Credit: Thorsten Feichtner
A hand-held laser pointer produces no visible recoil forces when it is “fired”– despite the fact that it releases a directed stream of light particles. The factor for this is just due to the fact that of its relatively huge mass compared to the very tiny recoil impulses that the light particles cause when they leave the laser guideline.
It has long been clear that optical recoil forces can certainly have a substantial effect on likewise little particles. For example, the tails of comets point away from the Sun partly due to light pressure. The propulsion of light spacecraft by means of light sails has actually likewise been talked about consistently, most recently in connection with the “starshot” task, in which a fleet of mini spacecraft is to be sent to Alpha Centauri.
Regular quadcopter drones as designs
In the journal Nature Nanotechnology, Würzburg physicists led by Professor Bert Hecht (Chair of Experimental Physics 5, Nano-Optics Group) have actually now revealed for the first time that it is possible to not just effectively propel micrometer-sized things in a liquid environment with light, however likewise manage them specifically on a surface area with all three degrees of freedom (two translational plus one rotational).
The tails of comets point away from the Sun partly due to light pressure. The propulsion of light spacecraft via light sails has likewise been gone over repeatedly, most just recently in connection with the “starshot” job, in which a fleet of miniature spacecraft is to be sent to Alpha Centauri.
” These motors are based on optical antennas established in Würzburg,– that is, tiny metallic structures with measurements less than the wavelength of light,” states Xiaofei Wu, a postdoc in the Hecht research group. “These antennas were particularly enhanced for getting circularly polarised light. In a more step, the received light energy is then produced by the motor in a particular instructions to create optical recoil force, which depends on the sense of rotation of the polarisation (counterclockwise or clockwise) and on either of 2 various wavelengths of light.”
Size comparison in between quadrocopter and microdrone. Credit: Xiaofei Wu
In doing so, they were inspired by regular quadcopter drones, where 4 independent rotors enable complete control of the motions. Such control possibilities use totally new alternatives for the normally very hard handling of nano- and micro-objects, for example, for the assembly of nanostructures, for the analysis of surface areas with nanometre precision, or in the field of reproductive medication.
Polymer discs with as much as four light-driven nanomotors
The Würzburg microdrones consist of a transparent polymer disc determining 2.5 micrometers in size. Approximately four separately addressable nanomotors made of gold are embedded in this disc.
” These motors are based on optical antennas established in Würzburg,– that is, small metal structures with measurements less than the wavelength of light,” states Xiaofei Wu, a postdoc in the Hecht research study group. In an additional step, the gotten light energy is then emitted by the motor in a specific direction to create optical recoil force, which depends on the sense of rotation of the polarisation (counterclockwise or clockwise) and on either of two various wavelengths of light.”
It was only with this concept that the researchers were able to control their microdrones efficiently and specifically. Due to the very small mass of the drones, severe velocities can be achieved.
The development of the microdrones was challenging. It started back in 2016 with a research study grant by the VW Foundation dedicated to dangerous tasks.
Precise fabrication based on single-crystal gold
The incredibly accurate fabrication of the nanomotors is essential for the function of the microdrones. Making use of accelerated Helium ions as a method to cut nanostructures from monocrystalline gold has actually ended up being a video game changer. In more steps, the drone body is produced using electron beam lithography. Finally, the drones need to be separated from the substrate and brought into service.
In further experiments, a feedback loop is being executed to automatically correct external impacts on the microdrones to manage them more exactly. Moreover, the research study group strives to complete the control options so that the height of the drones above the surface can likewise be controlled. And obviously, another goal is to attach practical tools to the microdrones.
Reference: “Light-driven microdrones” by Xiaofei Wu, Raphael Ehehalt, Gary Razinskas, Thorsten Feichtner, Jin Qin and Bert Hecht, 21 April 2022, Nature Nanotechnology.DOI: 10.1038/ s41565-022-01099-z.