Vasily Astratov Develops New Approach to Achieve Optical Super-resolution

Optical super-resolution is an extremely important and popular direction of research inthe areas of materials characterization and in life sciences. The resolution of conventional microscope systems has a fundamental limitation determined by the diffraction of light, typically half the wavelength of light. Increasing the resolution beyond the diffraction limit enables imaging the nanoscale world with visible light. The results may have dramatic consequences for industry, technology and research. It would allow visualization of the internal structure of metamaterials, biological cells, viruses and circuitry.

In this project CfM Professor Vasily Astratov developed a new approach to achieve optical super-resolution based on micron-scale dielectric microspheres placed in contact with investigated structures. His work shows that high-index microspheres immersed in a liquid are capable of picking up optical near-fields of nanoscale objects and projecting these fields into propagating far-fields. Thus, conventional microscopies can view the extraordinary fine features of nanoscale objects. The goals of his research are to understand the mechanisms of super-resolution imaging and to develop novel optical components that can boost the resolution of conventional microscopy systems.

 

The main result of this CfM study is that nanoplasmonic arrays can be visualized using high-index microspheres with ~l/7 resolution [1,2], where lis the wavelength of light. Microsphere-assisted imaging offers a series of advantages over conventional and solid immersion lens microscopies [3]. These advantages include improvements over diffraction-limited resolution, higher magnification, and smaller apertures.

 

Professor Astratov also performed fundamental studies of the optical and transport properties of an array of microspheres and observed novel polarization effects [4] and unusual waveguiding properties [5] which can be useful for developing various focusing, imaging, and waveguiding devices with polarization capability.

 

The key property for developing applications of super-resolution imaging by microspheres is an ability to controllably move the microspheres and align them with different surface nanostructures. CfM has developed a novel technology of embedding high-index microspheres in transparent thin-film matrices that can be easily translated along the surface of investigated structures. The thin film with embedded microspheres plays the part of a "magnifying glass" allowing one to see extraordinary small features with the resolution approaching ~l/7.

 

One more direction of our research is related to using tightly focused light beams produced by high-index microspheres, termed "photonic nanojets", for improving the pixel efficiency of mid-infrared imaging systems. We experimentally proved higher light sensitivity of the strained-layer superlattice infrared photodetectors integrated with microspheres on an order of magnitude. We developed techniques to align microspheres in device structures based on super-resolution imaging. The results are important for increasing detectivity, reducing dark currents and increasing the speed of mid-IR photodetector arrays.

 

 

[1]  V. N. Astratov and A. Darafsheh, Methods and systems for super-resolution optical imaging using high-index of refraction microspheres and microcylinders, US patent application 14042834 filed on 10/01/2013 with priority from original application on 06/07/2012.

[2]  A. Darafsheh, G. F. Walsh, L. Dal Negro, and V. N. Astratov, Optical super-resolution by high-index liquid-immersed microspheres, Appl. Phys. Lett101, 141128 (2012).

[3]  A. Darafsheh, N. I. Limberopoulos, J. S. Derov, D. E. Walker Jr., and V. N. Astratov, Advantages of microsphere-assisted super-resolution imaging technique over solid immersion lens and confocal microscopies, Appl. Phys. Lett104, 061117 (2013).

[4] A. Darafsheh, N. Mojaverian, N. I. Limberopoulos, K. W. Allen, A. Lupu, and V. N. Astratov, Formation of polarized beams in chains of dielectric spheres and cylinders,Opt. Lett38, 4208-4211 (2013).

  [5] K. W. Allen,A. Darafsheh,F. Abolmaali, N. Mojaverian, N. I. Limberopoulos, A. Lupu,and V. N. Astratov, Microsphere-chain waveguides: Focusing and transport  properties, accepted to Appl. Phys. Lett. (2014).

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