The world-leading super-lens technology based on nanoparticles
"We have experimentally realized a 100-nanometer optical focus. However, from a theoretical point of view, it is possible to obtain an optical focus of 10 nanometers or less. Furthermore, it is possible to make several optical foci or completed patterns at the same time. Since there is no part that moves like the probe used by the near-field scanning optical microscope, it is possible to use it in such fields as biology. If the technology we have realized is used between the optical communication and the direct circuit, it will be possible to deliver the optical information through an extremely small waveguide. As a result, we believe that it will be possible to provide a new approach to realize and utilize the optical information."
Resolution nearly three times higher than that shown by conventional optical lenses
The principle of conventional lens is based on the refraction of light, which means that it creates an optical focus by refracting light on the surface curve made of such a transparent material as glass. However, the smallest focus that be achieved by a conventional lens is the half of light wavelength used, that is, about 200 to 300 nanometers. Human beings have used lenses for more than 3,000 years; however, the basic principle used in making an optical focus by using the refraction of light has not changed. As a result, limitations are still inevitable when we follow such a principle. However, if lenses are made based on the scattering of light rather than the refraction of light, it is possible to overcome the fundamental limitation shown by the previous lenses and to make an optical focus that is smaller than the wavelength of light.
The research team led by Professor YongKeun Park has carried out research for over two years to develop a new super-lens technology based on the nanoparticles whose level of resolution is about three times higher than that of the previous optical lens. The idea related to such development was originally brought up by Professor YongKeun Park in 2010. During the whole R&D process, the research team went through numerous trials and errors to turn this idea into a reality.
First, the team focused on the application of the near-field scanning optical microscope (NSOM), which is a certified way of checking the existence of an acute focus. The experiment was carried out by forming a joint research team with Professor Yong-hun Cho from the Department of Physics, KAIST and Doctor Chung-hyeon Park, both of whom are experts in the field. While carrying out the research, the team found the problem related to the leakage of light from the scattering layer. It took about a year for the team to solve this problem.
To date, it has been impossible for conventional lenses to overcome their limitations for diffraction because of the loss of the near-field light. The near-field light can be regarded as light trapped within an object and light that is found in the vicinity of an object. When scattering occurs, it results in near-field light formation around the scattering object. Even if the near-field light itself disappears over propagation, the presence of the near-field can be detected by the scattering of nanoparticles because the scattered light from near fields can generate light information that can propagate to a distant place.
The research team led by Professor YongKeun Park exploited multiple light scattering resulting from randomly distributed nanoparticles in order to convert optical near-field information into far-field propagating light. To observe small objects, it is necessary to have a great deal of information on the near-field light. However, it is necessary to transform the near-field light that is not transmitted in the air into far-field light that can propagate in the air and, thus, can be detected at a distance. For this purpose, the concept of ‘scattering’ can be used to make light collide with the particle, which could lead to the transformation of the near-field light contained by an object into the remote-field light.
In order to develop the scattering super-lens technology, the research team led by Professor YongKeun Park used ordinary spray-paint sold in the market. Since the highly scattering nanoparticles can be concentrated in paint, each near-field light can be scattered to create another near-field and far-field light. In other words, instead of being eliminated, the subject information contained in near-field light is transformed into another form based on the sequential scattering process. In order to use the near-field light in such a way, it is necessary to follow the process of arranging the light information given by the remote-field light joining the layer of nanoparticles from the outside. Since it is possible to use such a type of lens by gathering light, the strength and direction of light can be controlled by using a device called the spatial light modulator, which can systematically control the optical wavefront. Through such a process, the scattering super-lens has been developed.
The resolution shown by the scattering super-lens is three times higher than the one shown by the previous optical lens. Since the previous optical lens relies on the refraction of light, it is impossible to adjust the focus to 1/3000 millimeter or less, which is smaller than the wavelength of light. However, by painting the particles that scatter light on the lens and adjusting the scattering light to become sharper, it is possible to adjust the focus to 100 nanometers or 1/10,000 millimeter. It may be possible to directly view live subcellular organelles or viruses through the scattering super-lens, which was impossible through the optical lenses of the past. By using the process of multiple scattering, the scattering super-lens makes it possible to deliver the optical information that cannot be transmitted through the previous type of lens to the destination by using a thin paint layer. The research team made such a discovery for the first time in the world and received a great deal of attention.
The research carried out by Professor YongKeun Park and his team is quite important since it provided a high level of resolution by merely using a thin paint film and the spatial light modulator. It can be regarded as a case of controlling the near-field light occurring through the scattering process. The research challenges the conventional notion of the necessity of using a medium with a high refractive index or to use a light source with a short wavelength such as ultraviolet rays of X-rays. The scientific journal Nature Photonics evaluated the research to be quite innovative, as it changed the idea of generating a light focus light by using the refraction of light, a concept that has been utilized by humankind for 3,000 years.
In the future, the scattering super-lens technology could be applied to various fields including bioimaging and lithography. Moreover, it could contribute greatly various fields by connecting light and electronic devices.
Prof. Park, YongKeun
2013 Annual Report