Physicists push microscopes beyond limits

Ever since Antony van Leeuwenhoek discovered the world of bacteria through the microscope in the late 17th century, humans have tried to peer deeper into the world of the infinitesimal.

However, there are physical limits to how accurately the body can be examined using traditional visual methods. This is known as the diffraction limit and is determined by the fact that light appears as a wave. This means that the focused image cannot be smaller than half the wavelength of light used to observe an object.

Attempts to break this limit with “super lenses” have all run into the obstacles of severe vision loss, making the lenses opaque. Now physicists at the University of Sydney have demonstrated a new way to achieve superlensing with minimal losses, breaching the diffraction limit by a factor of almost four times. The key to their success was to completely remove the superlens.

The research is published in Nature Communications.

The researchers say this work should allow scientists to further improve super-resolution microscopy. This could lead to the development of imaging in fields as diverse as cancer diagnosis, medical imaging, or archaeology and forensics.

Lead author of the research, Dr Alessandro Toñez from the University of Sydney’s School of Physics and Nano Institute, said: “We have now developed a practical way to implement superlensing, without a superlensing. To do this, we position our optical probe farther away from the object and collect both high-resolution and low-resolution information.” “By measuring far away, the probe does not interfere with the high-resolution data, which is a feature of previous methods.”

Previous attempts have attempted to create superior lenses using new materials. However, most materials absorb so much light that a superlens is useful.

“We overcame this by performing the hyperlensing process as a post-processing step on the computer, after the measurement itself,” said Dr. Tönnies. “This produces a ‘true’ image of the object by selectively amplifying the vanishing (or evanescent) light.” waves.”

Co-author Professor Boris Kuhlme, also from the School of Physics and Sydney Nano, said: “Our method could be applied to determine the moisture content of leaves more precisely, or be useful in advanced microfabrication techniques, such as non-destructive assessment” of the integrity of microchips. “This method can be used to reveal hidden layers in works of art, and may be useful in detecting artistic forgeries or hidden works.”

Typically, superlensing attempts have sought close access to high-resolution information. This is because this useful data decays dramatically with distance, and is quickly overwhelmed by lower-resolution data, which does not decay very quickly. However, moving the probe too close to an object distorts the image.

“By moving our probe further away, we can preserve the integrity of the high-resolution information and use post-observation technology to filter out the low-resolution data,” Associate Professor Kolme said.

The research was conducted using terahertz light at millimeter wavelength, in the region of the spectrum between visible and microwave.

“This is a very difficult bandwidth to work with, but it is very interesting, because in this range we can obtain important information about biological samples, such as protein structure, hydration dynamics, or for use in cancer imaging,” Associate Professor Kolme said. “.

“This technology is a first step in allowing high-resolution images while remaining a safe distance from the object without distorting what you see,” said Dr. Tonnies. “Our technology can be used in other frequency ranges. We expect anyone who performs high-resolution optical microscopy will find this technology interesting.” ”