Schematic of optically levitating a nanoparticle with a metalens in a vacuum. The metalens focuses a laser beam to produce chip-based optical tweezers. Credit: Kunhong Shen, Purdue University
Metalens-based style diminishes footprint, making optical traps practical for precision picking up and measurements.
Researchers have actually produced small chip-based optical tweezers that can be used to optically levitate nanoparticles in a vacuum. Optical tweezers– which utilize a firmly focused laser beam to hold living cells, nanoparticles, and other items– can be used for a variety of precision measurements and picking up applications. These optical traps are usually produced with bulky optical parts.
” By using an ultrathin metalens, we reduced the diameter of the focusing lens from about 25 mm to about 0.4 mm,” stated research study group leader Tongcang Li from Purdue University. “The chip-based style can be used to produce an incorporated and flexible optical system for studying near-surface forces by trapping an item less than 1 micrometer far from a surface area. It may likewise work for trapping cold atoms in a vacuum to study quantum processes.”
The metalens focuses a laser beam to create chip-based optical tweezers. These optical traps are normally produced with bulky optical components.
Researchers used a metalens to create chip-based optical tweezers that can optically levitate nanoparticles in a vacuum. An optical image of the metalens is revealed. To evaluate their brand-new optical style, the scientists assisted an intense laser beam onto the metalens to generate trapping forces.
Researchers used a metalens to develop chip-based optical tweezers that can optically levitate nanoparticles in a vacuum. An optical image of the metalens is shown.
In Optica, Optica Publishing Groups journal for high-impact research study, scientists at Purdue University and Pennsylvania State University report the very first awareness of on-chip optical levitation in a vacuum with an ultrathin metalens. Accomplishing this feat in a vacuum helps enhance the level of sensitivity of the system.
” Optically levitated particles can be used to develop accelerometers and gyroscopes that could potentially be utilized in navigation,” said Li. “Scientists are also utilizing optically levitated particles to look for dark matter and dark energy and to study gravity at short distances, which will deepen our understanding of nature.”
Toward a portable trap
This brand-new research grows out of previous work in which the scientists utilized optical levitation in a vacuum to produce the fastest human-made rotor and the most sensitive torque detector ever reported.
” As a next step, we wanted to make optical levitation technology more practical by reducing the system sufficient to make it portable,” said Li. “We started by reducing the size of the focusing lens by utilizing a metalens, a type of flat lens that uses nanostructures to focus light.”
In the new work, the scientists created a metalens consisting of thousands of silicon nanopillars. The diameter of the metalens had to do with 50 times smaller sized than that of the standard objective lens that they used prior to.
” Other research study groups have actually just recently shown metalens-based optical trapping in liquids,” said Kunhong Shen, the very first author of this work. “Although carrying out optical trapping in a vacuum helps minimize sound from liquid or air, it is likewise much more difficult to do.”
The scientists showed that a levitating nanoparticle might be moved between two different optical traps. Credit: Kunhong Shen, Purdue University
Levitating with a flat lens
To test their brand-new optical design, the scientists directed an intense laser beam onto the metalens to produce trapping forces. They then sprayed a watered down nanoparticle solution into the trapping location. When a nanoparticle becomes caught, it will look like an intense area that can be observed with an electronic camera. Photon detectors measured the nanoparticles movement in real time.
They revealed that the metalens could levitate a nanoparticle in a vacuum at a pressure of 2 × 10-4 Torr– about 1/4,000,000 air pressure– without requiring any feedback stabilization. They were likewise able to transfer a levitating nanoparticle between two different optical traps.
” Our metalens is a nanostructure layer with a thickness of merely 500 nm and a big mathematical aperture of about 0.9. It offers similar performance as a conventional bulky lens,” said research group leader Xingjie Ni from the Pennsylvania State University. “The metalens is totally vacuum-compatible. And more remarkably, we can flexibly design it to perform additional functions, for example, filtering out low-spatial-frequency elements from the focusing light, which we have actually proven to be beneficial for optical levitation of nanoparticles.”
The researchers are now working to improve the tiny levitation devices by focusing and improving the transmission performance of the metalens. They likewise want to make the diameter of the metalens even smaller to make optical levitation more useful for real-world applications.
Reference: “On-chip optical levitation with a metalens in vacuum” by Kunhong Shen, Yao Duan, Peng Ju, Zhujing Xu, XI CHEN, Lidan Zhang, Jonghoon Ahn, Xingjie Ni, and Tongcang Li, 21 October 2021, Optica.DOI: 10.1364/ OPTICA.438410.
