Scientists Generate Light's "Spin" from a Gold Nanorod
A research team from Tokyo University of Science and the Institute for Molecular Science in Japan has demonstrated a method to generate circularly polarized light, also known as light's "spin," from a gold nanorod. The technique involves exciting the nanorod with an electron beam at a point away from its center. The findings were published in the journal Nano Letters.
Research Overview and Key Finding
The study demonstrated that striking a gold nanorod approximately 150 nanometers long with an electron beam at an off-center position causes the emitted light to take on a rotating, circularly polarized character. The strength of this polarization effect was found to increase the farther the beam struck from the nanorod's center.
Scientific Background
Light polarization describes the oscillation pattern of its electric field. Linearly polarized light oscillates along a fixed axis, while circularly polarized light rotates, creating a helical pattern.
Controlling this "spin" at the nanoscale is a recognized challenge in photonics, as the geometry of a material often dictates the polarization of emitted light.
Elongated nanostructures like nanorods typically produce light that is linearly polarized along their long axis.
Methodology and Verification
The research team, led by Professor Mark Sadgrove with co-first authors Dr. Yining Xuan and Master's student Daito Miyazaki, placed the gold nanorod on an ultra-thin optical fiber to confirm the circular polarization. This type of fiber has a property where the direction light travels through it depends on whether the nearby light is spinning clockwise or counterclockwise. By measuring which end of the fiber the light emerged from, the researchers confirmed the generation of circularly polarized light.
Professor Sadgrove provided an analogy for the principle:
"If you have ever flicked one end of a pen lying on a table, you will be familiar with the fact that as well as moving forward, the pen also tends to rotate."
He noted that while the principle of light generation is different, the concept of introducing an imbalance to produce spin is applicable.
Regarding the measurement technique, Professor Sadgrove stated, "Although the effect seems simple, it was only our familiarity with the properties of optical fibers, which allowed us to actually measure it."
The experimental results matched prior simulation predictions. Shifting the electron beam's point of impact from one side of the nanorod to the other caused the direction of light travel through the fiber to reverse, indicating a switch in the light's rotation direction.
Publication Details
The related research paper was made available online on February 9, 2026, and published in Volume 26, Issue 6 of the journal Nano Letters on February 18, 2026.
Potential Applications
The study presents a method to control the spin of light using a simple nanostructure. Potential applications identified by the research include:
- Integrated Optical Circuits: Where compact and efficient light control is needed.
- Information Processing: Enabling new methods for encoding, routing, and processing information with light.
- Advanced Technologies: Supporting research in areas such as quantum communication and photonic technologies. The method could be applied to control the spin of single photons.