Let us shed some light: CEITEC scientists develop a technique to envisage metasurfaces – the future of optics


Sunlight presents the morning to you. The light from your bedroom lamp soothes your bedtime reading. The light has become an important part of your life, day and night.


The study of the behavioral properties of light (optics) is evolving constantly making this fascinating field of science even brighter.


Scattering of light to create a precise pattern and sending the light beam to a particular direction is a sought after theme. Conventional optical lenses (eye, camera, microscope, etc.) are curved, which scatter light in a limited fashion.


In the recent past, nanotechnologists have designed a flat-thin material called ‘metasurfaces,’ armed to scatter light in attractively different processes that a traditional curved lens cannot achieve.


Meta suggests something ‘beyond’, which is not found in nature. Metasurfaces are peppered with a series of nanomaterials, arranged in a way that could scatter light unconventionally – ‘beyond-natural-means’.


The research groups of Prof. Tomáš Šikola and Prof. Radim Chmelík of CEITEC-BUT have collectively devised a method to study the metasurfaces (1).



Miniaturization brings sophisticated optical components


“The metasurfaces provide you the opportunity to assemble your device and form the light-beam in a relatively small area (e.g. ideal for optical circuits),” says Prof. Šikola, “Though, it is always difficult to harness light in a small space, due to its diffracting property; these artificial elements can reach sub-wavelengths, beyond the diffraction limit.”


Prof. Šikola asserts, “When we are in the visible range, it is impossible to achieve a resolution below 0.3 micrometer; but with metasurfaces, we can go 1 order magnitude below." 


"In Raman spectroscopy, achieving a resolution of < 0.3-0.4 micrometer is difficult but just by adding some metallic tips (nano-antennas) as the metasurface, we can acquire information from an area of 10-20 nanometres."  


Prof. Tomáš Šikola (Photography by Emil Gallík)



Can we capture the light-shaping effects of the metasurfaces?


To quantitatively study the effects of the metasurfaces and monitor their light-shaping capabilities, it is important to analyse the light scattered by them.


Quantitative Phase imaging microscopy is the answer – and hence, brings in Prof. Radim Chmelík, an expert in that technique.


“It is a progressive method in imaging, particularly important in biology. It allows us to image live cells without staining, non-invasively – observing them in a nearly natural condition”, states Prof. Chmelík.


“We are approaching the practice to develop relevant instruments (e.g. holographic microscope, developed in the Chmelík group) which could apply this imaging technique.”



Prof. Radim Chmelík (Photography by Emil Gallík)



Why is the technique so special?


In a conventional microscope, there are two paths; the signal path (light reflected from the sample) and the reference path (light reflected from a reference, e.g. a mirror). For this special case, Dr. Petr Bouchal (the lead scientist of the study) planned to combine the paths together.   



Dr. Petr Bouchal (Photography by Emil Gallík)


Dr. Bouchal revealed, “Thanks to the system, we are able to measure these metasurfaces quantitatively in high resolution. It is possible to perceive the individual nano-antenna – the building block of the metasurfaces."



Dr. Petr Dvořák



Dr. Petr Dvořák, another scientist involved in this research adds, "Only scanning near-field optical microscopy, a lengthy small-field-capturing process, has achieved this in the past. With our method, we can visualize a large field of view in a shorter time."



Imaging metasurfaces (Left - microscopy image of the metasurface, Right - phase image of the same metasurface, Inset - an array of four nanoantennas) (Image courtesy: Dr. Bouchal)



Prof. Chmelík expresses, "In the future, our microscopy technique will not only study the effect of metasurfaces but also use them to build new optical systems. The blend of Prof. Šikola’s group – an expert in fabricating metasurfaces – and our knowledge in microscopy could conjointly make this possible."



The credible applications


“We are in the age of miniaturization. Development of efficient mobile phone cameras stacking countless lenses is on the cards. Applications in life science research as biosensors [Biosensor is a device which uses a living organism or biological molecules (e.g. enzymes or antibodies), to detect the presence of chemicals] are also feasible” utters Dr. Bouchal.




The imaging module (Image courtesy: Dr. Bouchal)



Dr. Chmelík voices passionately, “Our research will augment cancer research, with an opportunity to observe the cancers cells in living conditions.”




References

  1. Bouchal, P. et al. High-Resolution Quantitative Phase Imaging of Plasmonic Metasurfaces with Sensitivity down to a Single Nanoantenna. Nano Lett. 19(2), 1242–1250

 


Written by Somsuvro Basu


Publication date: 08.07.2019