A method for local evaluation of optical properties of heterogeneous media of various nature using a pulsed terahertz solid immersion microscope
V. A. Zhelnov1, D. D. Rybnikov1, K. I. Zaytsev1, N. V. Chernomyrdin1;
1Prokhorov General Physics Institute of RAS, 38 Vaviliva str., Moscow, 119991, Russia
Abstract
A novel method of pulsed terahertz (THz) solid immersion microscopy operating in reflection mode has been developed. It combines the advantages of the resolution-enhancement approach based on solid immersion effect with those of time-domain spectroscopy to obtain comprehensive information about biological objects and condensed media. Our experimental setup is utilized a THz solid immersion imaging system and employs a pair of low-temperature GaAs-based photoconductive antennas (PCAs—i.e., an emitter and a detector of broadband THz pulses) to acquire images across a wide spectral range. A three-dimensional representation of the sample is constructed through raster scanning, generating a data array that can be analyzed both in the native time domain and the derived frequency domain, thus enabling multifaceted analysis of the THz signal for enhanced information extraction. Our results demonstrate that the microscope's resolution δ is contingent upon the domain of THz signal representation. When operating in the time domain, the resolution ranges from 0.136λc to 0.20λc, where λc ≈ 360 µm corresponds to the carrier frequency fc ≈ 0.83 THz. Analysis in the spectral domain (0.5–1.7 THz) yields resolutions of 0.147λ to 0.304λ for amplitude detection mode and a notably superior 0.047λ to 0.156λ for phase detection. This enhancement in the phase-domain resolution is directly attributable to the inherent nonlinearity of the phase image formation process. The developed THz micro-spectroscopy method could be applied in the field of biomedical science, the non-destructive testing of materials, and the physics of condensed media, where THz spectral imaging must be performed on a scale of 10 to 100 microns. Consequently, this modality represents an ideal solution that combines essential subwavelength resolution with obtaining local spectroscopic data.
Speaker
Vladislav Zhelnov
Prokhorov General Physics Institute of the Russian Academy of Sciences
Russia
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