Physics researchers at the University of Bath in the UK have discovered a new physical effect related to the interaction between light and twisted materials-an effect that may have an impact on emerging nanotechnology in communications, nanorobots, and ultra-thin optical components .

In the 17th and 18th centuries, the Italian master craftsman Antonio Stradivari made musical instruments of legendary quality, the most famous being his (so-called) Stradivari violin. What makes the musical output of these instruments both beautiful and unique lies in their special timbre, also known as timbre or tone quality. All instruments have timbres-when playing a note (a sound with a frequency of fs), the instrument will produce harmonics (the frequency is an integer multiple of the initial frequency, ie 2fs, 3fs, 4fs, 5fs, 6fs, etc.).

Similarly, when a certain color of light (frequency fc) shines on a material, these materials will produce harmonics (light frequency 2fc, 3fc, 4fc, 5fc, 6fc, etc.). The harmonics of light reveal complex material properties that have applications in medical imaging, communications, and laser technology.

For example, almost every green laser pointer is actually an infrared laser pointer whose light is invisible to the human eye. The green light we see is actually the second harmonic (2fc) of the infrared laser pointer, which is generated by a special crystal inside the pointer.

In musical instruments and shiny materials, some frequencies are "forbidden"—that is, they cannot be heard or seen because the musical instrument or material actively cancels them. Because the clarinet is a straight cylindrical shape, it suppresses all even harmonics (2fs, 4fs, 6fs, etc.) and only produces odd harmonics (3fs, 5fs, 7fs, etc.). In contrast, the saxophone has a tapered and curved shape, allowing all overtones and producing a richer and smoother sound. A bit similar, when a specific type of light (circularly polarized) is irradiated on metal nanoparticles dispersed in a liquid, the odd harmonics of the light cannot propagate in the direction of light travel, and the corresponding color is prohibited.

Now, an international team of scientists led by researchers from the Department of Physics at the University of Bath has found a way to reveal prohibited colors, which is equivalent to discovering a new physical effect. To achieve this result, they "bent" their experimental equipment.

Professor Ventsislav Valev, who led the research, said: “The idea that the distortion of nanoparticles or molecules can be revealed by the even harmonics of light was first proposed by the young doctoral student David Andrews 42 years ago. David thinks His theory is too elusive to be experimentally verified, but we proved this phenomenon two years ago. Now, we have found that the distortion of nanoparticles can also be observed in the odd harmonics of light. It is especially gratifying. Yes, the provider of the relevant theories is our co-author and today's well-known professor-David Andrews!

Take music as an analogy. Until now, scientists who study distorted molecules (DNA, amino acids, proteins, sugars, etc.) and nanoparticles in water (elements of life) have illuminated them at a given frequency, or observed the same frequency or Its noise (dissonant partial overtones). Our research opens the study of the harmonic characteristics of these twisted molecules. Therefore, we can appreciate their "timbre" for the first time. From a practical point of view, our results provide a direct, user-friendly experimental method to understand the interaction between light and distorted materials like never before. This interaction is at the core of emerging nanotechnology in communications, nanorobots, and ultra-thin optical components. For example, the "twist" of the nanoparticle can determine the value of the information bit (left-handed or right-handed twist). It is also present in the propeller of the nanorobot and can affect the propagation direction of the laser beam. In addition, our method is suitable for small-volume lighting and for the analysis of natural chemical products. These products are expected to be used in new medicines, but the available materials are often scarce. "

PhD student Lukas Ohnoutek also participated in the study. He said: "We almost missed this discovery. Our initial equipment was not well "tuned", so we never saw the third harmonic. I started to lose hope. But we had a meeting, identified potential problems and investigated them systematically until we found them. It is great to experience the scientific method in work, especially when it leads to scientific discoveries!"

Andrews added: “Professor Wallev led an international team to achieve a real first in the field of applied photonics. When he invited me to participate, it brought me back to theoretical work from my PhD research. After so many years, I saw It’s amazing that it blooms and bears fruit."

 -This press release was originally published on the University of Bath website

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