Light and tiny bubbles have been used to propel microparticles at forces many times greater than previously achieved in an innovative technique, which could have significant implications in the development of micromotors and optical devices for use in solar cells.
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Ben-Gurion University of the Negev Researchers demonstrate a light-generated bubble for microparticle propulsion. Panel (a) shows the 42 μm diameter spherical particle and the 405 nm laser beam as the respective dark and bright patches. Panel (b) shows that 40 milliseconds later the microsphere has traversed a distance roughly 10 times its size. (Credit: Ben-Gurion U.)
What we ultimately hope to achieve is a highly accurate, passive technology for use in a concentrated solar device that would follow the sun without the need for a mechanical tracking method.
Dr Avi Niv, Ben-Gurion University of the Negev, Israel
The current way for using light to manipulate micro and nano objects is based on momentum transfer from the light beam to the solid object, explains Niv. The fact that light has a momentum was known back in the late 19th century but it was only in the 1970s that a way to actually put it to work was found. This paved the way for optical tweezers, as well as optical cooling. However, the momentum of light is only feeble and so the forces from optical tweezers are no more than a few pico-Newton at best.
While light beams deliver only little momentum, it is not so for its energy. Indeed light is the most proficient energy carrier in the known universe, the solar flux that feeds the earth and optical communication networks are examples of this.
Dr Avi Niv, Ben-Gurion University of the Negev, Israel
With this in mind, the Researchers plan to use the energy of light rather than its momentum to inflict motion. Their work, published in Scientific Reports, shows that the Researchers were able to convert energy created from light into kinetic motion using nano-sized, laser-generated bubbles. As the bubble grows, its acts as a propulsion mechanism for the surrounding microparticles. Mechanical manipulation of micro and nano-scaled objects is significant in biology, surface science and microfluidics, and also for micro machines.
A micron-sized object was propelled at unprecedented speeds of close to one meter-per-second – much faster than in present devices – while still maintaining motion direction control. Once the bubble initiates movement and bursts, there is no trace of the vapour and the system returns to the original state, meaning the action can be initiated repeatedly.
“What the article shows is that this change in paradigm yielded in a method that demonstrated forces six orders of magnitude larger than what is common with optical tweezers,” says Niv. “There's no doubt in my mind that the paradigm change from momentum to energy transfer would prove to be profound for the technology of micro mechanics, be it with bubbles as we showed or by other ways that I, for now, cannot think of. This is to me the source of innovation in this work.”
Niv explains that the first aim of the Researchers is to use this method to make a substance with light activated optical properties – so-called reactive optics.
An example of what we have in mind is in the form of an optical device with the ability of being switched from opacity to transparency depending on the intensity of light that falls on its face. In fact, we started by thinking of such a substance and realized that a paradigm shift is needed once found that available methods are simply not powerful enough for our needs.
Dr Avi Niv, Ben-Gurion University of the Negev, Israel
The Researchers are currently addressing cost-effective renewable energy production by working on ground-breaking light management technique for solar-cells based on this approach.
“Progress is well on the way and we are hoping to share exciting results sometime soon,” states Niv. “We are also thinking of light-controlled microfluidics and micro-engines but these are only preliminary ideas at this stage. Maybe our most immediate aim is, however, to expose this work to relevant crowds hoping to foster discussion that will help us to better understand what we have and what can be done with it.”
Microparticle Bubble Propulsion
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Reference: University of the Negev - Eureka
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