Influence of object dielectric properties on spatial resolution of a terahertz solid immersion microscope

Abstract

Terahertz (THz) solid immersion (SI) microscopy is an imaging technique that provides subwavelength spatial resolution that has found many applications in recent decades [1-3]. One of the features of SI optical systems is the dependence of its spatial resolution on the optical properties of the object. In our work we have carried out a numerical analysis using the finite-difference time-domain method to reveal the object-dependent spatial resolution of this approach [4]. Obtained results have shown that the system resolution remains strongly sub-wavelength 0.15–0.4λ for the wide range of sample refractive indices n=1.0–5.0 and absorption coefficients α=0–400 cm−1 by power. We also implemented experimental study using original continuous-wave THz microscope based on solid immersion effect and a set of objects with distinct refractive indexes. We noted two different modes of operation of the SI microscope. The first is the total internal reflection mode, which is achieved when the refractive index of the object is low and evanescent waves are excited. And the second is the ordinary reflection mode, which occurs when the refractive index of the object is high and total internal reflection was not obtained. Results are general and can be applied for the analysis of solid immersion lens operating in other spectral ranges.

[1] N.V. Chernomyrdin et al., Applied Physics Letters 110(22), 221109 (2017).
[2] N.V. Chernomyrdin et al., Applied Physics Letters 113(11), 111102 (2018).
[3] N.V. Chernomyrdin et al., Optical Engineering 59(6) 061605 (2020).
[4] V.A. Zhelnov et al., Optics Express 29(3), 3553-3566 (2020).


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Vladislav Zhelnov
Bauman Moscow State Technical University, General Physics Institute of the Russian Academy of Sciences
Russian Federation

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