Breaking the diffraction limit and seeing "near field optics"!

"This is the only optical microscopy that does not rely on fluorescent labeling and can break the diffraction limit." Eric Betzig, winner of the Nobel Prize in Chemistry in 2014, participated in the creation of "near field optical technology", which has attracted wide attention in China in recent years.

On April 18, the 743rd symposium of the Xiangshan Science Conference, with the theme of "Multi-field condition Ultra-high resolution near-field optics", was held in Beijing.

Experts attending the meeting believed that near field optics technology has unique advantages such as wide applicability, wide spectrum compatibility, nondestructive testing and no labeling, and has great application potential in condensed matter physics, semiconductor devices, biological detection, terahertz technology and other aspects. It is necessary to gather domestic research strength of near field optics, promote the development of technology and theory in this field as soon as possible, and enhance international influence.

Centenary vision come true

Tiny objects are magnified thousands of times, and the rich details of various substances are slowly unfolded, greatly expanding human's view of the natural world -- this is the "super power" endowed by the light microscope. However, it is not possible to increase the magnification infinitely. Because of the diffraction effect of light wave, the resolution of traditional optical microscopes cannot exceed half of the wavelength of light. This is mainly because the traditional optical microscope only collects and utilizes the "far field" optical information of the object, while the "near field" hidden wave carrying more detailed surface information of the sample cannot be detected and utilized. Therefore, optical observation requires holding objects at a distant position, and "far-field" optical information is collected.

Dai Qing, one of the executive chairmen of the conference and a researcher at the National Nanoscience Center, introduced in the keynote report of the conference that scientists have realized that in order to break through the diffraction limit to achieve ultra-high resolution optical imaging, the "near-field" optical information of an object must be effectively used. In 1928, the famous physicist Albert Einstein and the British and Irish scientist Edward Hutchinson Synge proposed the design concept of two near-field optical microscope designs at almost the same time in the communication. However, the technology was not available to control object spacing and transverse scanning with nanoscale precision, so their ideas remained on paper.

"After nearly one hundred years, and the unremitting efforts of several generations of researchers over the last hundred years, with the rise of scanning probe technology microscopy, the near field optical microscopy has formed the aperture (a-SNOM) and scattering (s-SNOM), the two most important technical paths, which have turned the ideas of two scientific pioneers into reality." Dai Qing said.

From the lab to commercialization

Experts at the conference believe that the continuous progress of near field optics technology is mainly due to the development of nano science and technology.

In 1984, scientists were the first to achieve aperture near-field optical microscopy with a resolution of 20 nanometers through the invention of a chemically etched quartz crystal probe first coated with an aluminum film. A few years later, the invention of the metal film coated fiber optic probe further improved the resolution to more than 12 nanometers.

After the 1990s, the scattering near field optical microscope was developed gradually. Especially after 1998, Fritz Keilmann, a German scientist, created the infrared band scattering near field optical microscope and promoted its commercialization.

"Today, with the rapid development of nanotechnology, the development and application of near-field optics technology has also entered a fast lane," Dai said.

As a powerful characterization tool in nanoscience, near-field optical microscopy has a unique advantage in detecting the optical response of nanointerfaces. At present, its instrument form has been basically stable, and relatively successful commercial products have appeared.

These instruments have been widely used in many frontier scientific fields such as optics, condensed matter physics, chemistry, biology and materials science. For example, the team of Dong Zhenchao from the University of Science and Technology of China realized Raman spectral imaging of a single molecule by using the field enhancement effect of the scattering near-field optical probe, and the team of Dai Qing from the National Nanoscience Center discovered the optical negative refraction effect in the heterostructure of two-dimensional materials by using the scattering near-field optical microscope and realized its dynamic regulation. Li Peining's team at Huazhong University of Science and Technology has demonstrated the existence of "ghost" polarik electromagnetic waves in birefringent crystals through near-field optical microscopy.

Experts attending the meeting believed that as the research entered the atomic scale, quantum effects became more significant, and this scientific frontier put forward new requirements for near field optics technology. Efforts should be made to strengthen the integration of near field optics technology with multiple physical fields such as low temperature, strong magnetic field and strong light field, so as to meet the needs of high spatial resolution optical characterization and multi-physical field regulation in the field of quantum materials research.

Discipline development initiative

In China, near field optics started late but developed rapidly, gradually forming a young and energetic research team. In 1997, Zhu Xing, a professor at the School of Physics of Peking University, introduced the first near-field optical microscope with aperture in China, and later independently developed the first low-temperature near-field optical microscope with aperture in China.

Now, after more than 20 years of development, domestic near-field optics related research has formed a blossoming situation. A survey of the literature shows an exponential increase in the number of papers published by Chinese academics. However, experts have pointed out that there are still problems in this field, such as lack of instrument innovation, incomplete theoretical system in the stage of follow-up and less overall academic exchanges.

In view of these practical problems, the experts at this meeting put forward "three ones" initiatives for the development of near-field optics in China, including "one project", "one conference" and "one institute", that is, to try to arrange a key research and development project of near-field optics, hold an influential international academic conference on near-field optics as soon as possible, and propose the establishment of a professional association of near-field optics.

Experts at the meeting called for efforts to be made in the research and development of instruments and equipment and localization of near-field optical instruments as soon as possible, to fully tap the potential of near-field optical technology in multi-physical field conditions and ultra-high resolution, and to lay a foundation for original research in frontier science fields.