Quantitative super-resolution solid immersion microscopy via refractive index profile reconstruction

Abstract

Solid Immersion (SI) microscopy is a modern imaging modality that overcomes the Abbe diffraction limit and offers novel applications in various branches of visible, infrared, terahertz, and millimeter-wave optics. Despite the widespread use, SI microscopy usually results in qualitative imaging. Indeed, it presents only the raw distributions (in the image plane) of the backscattered field intensity, while unlocking the information about the physical properties of an imaged object, such as its complex refractive index (RI) distribution, requires resolving the inverse problem and remains a daunting task. In this paper, a method for resolving the SI microscopy inverse problem is developed, capable of reconstructing the RI distribution at the object imaging plane with subwavelength spatial resolution, while performing only intensity measurements. The sample RI is retrieved via minimization of the error function that characterizes discrepancy between the experimental data and the predictions of analytical model. This model incorporates all the key features of the electromagnetic-wave interaction with the SI lens and an imaged object, including contributions of the evanescent and ordinary-reflected waves, as well as effects of light polarization and wide beam aperture. The model is verified numerically, using the finite-element frequency-domain method, and experimentally, using the in-house reflection-mode continuous-wave terahertz SI microscope. Spatial distributions of the terahertz RIs of different low-absorbing optical materials and highly absorbing biological objects were studied and compared to a priori known data to demonstrate the potential of the novel SI microscopy modality. Given the linear nature of the Maxwell’s equations, the developed method can be applied for subwavelength-resolution SI microscopy at other spectral ranges.

Terahertz technology in intraoperative neurodiagnostics: A review

“…Such THz systems allow to study the effective dielectric response of tissues, J o u r n a l P r e -p r o o f which is spatially-averaged over the λ 2 beam spot area of an optical system 17 . However, dimensions of some structural features of neural tissues are comparable to the THz wavelengths, and modern high-resolution THz optical systems are capable of distinguishing them 40,41 . Studying the effects of Mie scattering on such structural elements of neural tissues and development of novel approaches to describe the THz radiation transport in heterogeneous tissues containing such elements are topical problems of THz biophotonics, which still remain unaddressed 10 .…”

Frontiers in Terahertz Imaging Applications beyond Absorption Cross-Section and Diffraction Limits

“…Such THz bioimaging is further improved via reconstruction with a subwavelength resolution of the spatial distribution of the target sample. Analytical, numerical, and experimental studies of the material complex refractive index within the solid immersion (SI) microscopy paradigm were introduced (Figure B) . Using a continuous-wave THz SI microscope, the subwavelength resolution was achieved by measuring complex biological tissues ex vivo.…”

“…Markers I and II in the image are the gray matter (cortex) and white matter, respectively. Markers III and IV also indicate the accumulation of tumor cells and destroyed parts . (A) Adapted with permission from ref .…”

“…Copyright 2020 Elsevier. (B) Reprinted with permission from ref . Copyright 2021 Optical Society of America, .…”

Single-scan multiplane phase retrieval with a radiation of terahertz quantum cascade laser

“…The increasing interest in the terahertz (THz) frequency range in recent decades has given rise to a new branch of techniques and algorithms for the non-contact evaluation of surface and subsurface features of various samples and materials. In this field, THz imaging [1][2][3] represents one of the most promising approaches, since it provides spatially resolved information about the investigated objects. THz phase imaging (THz PI) [4,5], which includes pulse time-domain holography (PTDH) [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] as well as continuous wave (CW) holography [23][24][25][26][27][28][29][30], Hartmann wavefront sensing [31][32][33][34][35], shearorgaphy [36], ptychography [37][38][39][40][41], and other phase retrieval techniques [42][43][44][45]...…”