A new nanometre-scale distance measurement system, a kind of nanometric “optical ruler,” was developed by a research group at the Nanyang University of Technology in Singapore (NTU).
Currently there is a limit, called a “diffraction limit,” for which optical devices can only display a certain distance from the wavelength of the light used, more or less half of it, in a way that is considered to be reliable.
The diffraction limit is therefore higher than 400 nanometers, taking into account half of the wavelength of near-infrared light. We are talking about a very small distance, measurable in 100 microns and 250 times smaller than the width of a human hair.
However, this resolution is not sufficient to measure objects such as viruses and nanoparticles, which have a size of 100 to 10 nanometres. Therefore, indirect and non-optical methods are used to carry out measurements at the nanometre scale. These methods are not only complicated and very expensive, but are not always reliable.
Researchers Nikolay Zheludev and Guanghui Yuan describe in the new study a new optical mode to measure these distances. The new method can measure the smallest distance ever measured directly using near-infrared light.
With this method, according to the theoretical calculations they have done, it would be possible to measure distances up to the size of a single atom. They created a device with a 100 nanometer thick gold film characterized by 10,000 small slits to obtain diffraction of the laser light and to exploit an optical phenomenon known as “super-oscillation.”
“What makes it work is the precise pattern in which the cracks are arranged. There are two types of slits in the model, perpendicular to each other. When the polarized laser light hits the gold film, it creates an interference pattern with extremely small characteristics, much smaller than the wavelength of light,” explains Yuan himself.
It is not the first attempt to use super-oscillation for measurements of the optical type, but according to Zheludev, this technique is “an important improvement.”
Any applications? According to the researchers, such a method could be applied in various areas, from precision control in electronics to monitoring the integrity of nano-devices.
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