A Technion student has just smashed the world record for light resonance

Graduate student Jacob Kher-Alden created a floating resonator which exhibits resonant enhancement by 10 million circulations of light, compared to about 300 circulations in previous models.

By DONNA RACHEL EDMUNDS
Jacob Kher-Alden (photo credit: COURTESY TECHNION)
Jacob Kher-Alden
(photo credit: COURTESY TECHNION)
A graduate student at the Technion – Israel Institute of Technology has set a new world record in light resonance, smashing the previous record set by a Nobel Prize winner.
A resonator is a device that traps waves and enhances them by bouncing them back and forth on surfaces. Guitars, for example, resonate the sound waves made by strumming the instrument's strings, amplifying the sound made. But resonators also exist for light waves, acting in effect as a transistor within systems based on optics.
They can be made up of just two surfaces, bouncing the wave between them, but the more surfaces that are added, the more resonance is achieved. The ultimate is therefore to create a perfect sphere, creating surfaces in every direction within a three-dimensional object. At that point, the creation of a resonator moves from being a physics question to one of engineering, since even a stem holding the sphere can create distortion that reduces the impact of the resonator.
According to the Technion, the world's first micro-resonator was demonstrated in the 1970s by Arthur Ashkin, winner of the 2018 Nobel Prize in Physics, who presented a floating resonator. Yet, despite the success of his innovation, the research direction was soon abandoned.
Now graduate student Jacob Kher-Alden, under the supervision of Prof. Tal Carmon, has built upon Ashkin's work, creating a floating resonator which can exhibit resonant enhancement by ten million circulations of light, compared to about 300 circulations in Ashkin's resonator.
“If we take light that has a power of one watt, similar to the light of the flash on a cell phone, and we allow it to rotate back and forth between these mirrors, the light power will be amplified to about a million watts, equal to the electricity consumption of a large neighborhood in Haifa, Israel," Carmon said. "We can use the high light output, for example, to stimulate various light-matter interactions at the region between the mirrors.” 
Prof. Tal Carmon (Credit: Courtesy)
Prof. Tal Carmon (Credit: Courtesy)
This happens by one photon of light within the resonator making ten million circular trips as it bounces around inside, but as matter 'records' each passing of the photon as one particle of light, it reacts as though that one particle was 10 million particles passing through just once.
The resonator used by Kher-Alden is made up of a drop of highly transparent oil about the quarter of the thickness of a human hair, held in air using light. In this way, the drop is held without any material support, which eliminates distortions in the sphere. The technique is known as 'optical forceps.'
"This ingenious optical invention, the optical forceps, is used a lot in life sciences, chemistry, micro-flow devices and more, and it is precisely the optical researchers who hardly use it – a bit like the cobbler walking barefoot," Carmon said. "In the present study, we show that optical forceps have enormous potential in the field of optical engineering. It is possible, for example, to build an optical circuit using multiple optical forceps that hold many resonators and control the position of the resonators and their shape as needed."

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The microscopic proportions of the droplet also increase sphere integrity, because at that scale gravity has a minimal effect on the surface tension of the droplet. And while the droplet is held within a laser beam, it receives light from another fiber, which also receives the light back after it has passed through the resonator.
By taking readings from the light within the fiber, the researchers were able to figure out what was happening inside the droplet. The results show a world record in light amplification: 10,000,000 rotations that pass through a cross-sectional area of about a micron squared, increasing the light 10 million times.


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