Solving inverse problem of terahertz solid immersion microscopy for biomedical applications

Abstract

During the past decades, optical systems based on Solid Immersion (SI) effect have found numerous applications [1,2]. However, in most cases, images obtained by the SI microscopes represent only the back-scattered field intensity distributions over the object plane, with no attempts to access its physical properties, such as a complex refractive index. We propose a novel method for resolving the SI microscopy inverse problem, aimed at quantitative estimation of distributions (over the image plane) of the object optical properties and related physical quantities via minimization of an error functional, that minimizes a discrepancy between experimental data and a theoretical model of the electromagnetic beam focusing by a SI lens [3,4]. This model considers polarization state of the incident electromagnetic wave, as well as an interplay between the ordinary-propagating waves and evanescent waves that originate at the SI lens – object interface thanks to the total internal reflection phenomenon. The developed model was verified numerically and implemented experimentally using an in-house continuous-wave reflection-mode terahertz (THz) SI microscope [5,6]. The obtained results demonstrate the potential of applying the developed method for quantitative evaluation of the object optical properties in different branches of THz science and technology, with an emphasis on THz biophotonics.

[1] Applied Physics Letters 110 (22), 221109 (2017).
[2] Applied Physics Letters 113 (11), 111102 (2018).
[3] IEEE Transactions on Terahertz Science and Technology 5 (5), 817–827 (2015).
[4] Optica (under consideration in 2021).
[5] Optical Engineering 59 (6), 061605 (2019).
[6] Optics Express 29 (3), 3553 (2021).

Speaker

Nikita V. Chernomyrdin
Prokhorov General Physics Institute of the Russian Academy of Sciences
Russia

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