Superresolution THz pulsed solid immersion microscopy

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A reflection-mode THz pulsed solid immersion (SI) microscope is developed to combine the superresolution capabilities of SI optics and the advanced information content offered by THz pulsed imaging. It uses a wide-aperture silicon SI lens and a pair of photoconductive antennas (PCAs—i.e., an emitter and a detector of broadband THz pulses) to perform superresolution THz spectral imaging. By raster scanning of a sample, the 3D image is collected that can be represented in the time or frequency domains, with diverse opportunities for the THz signal analysis. The microscope resolution δ depends on the THz data presentation. When analyzed in the time domain, the resolution is 0.136λc–0.20λc (the wavelength λc≈360 μm corresponds to the carrier frequency νc≈0.83 THz). In the spectral domain (the 0.5–1.7 THz frequency range), it is 0.147λ–0.304λ and 0.047λ–0.156λ in the amplitude and phase detection modes, respectively. The superior phase-domain resolution is attributed to the nonlinearity of the phase image formation procedure. The ability of THz pulsed SI microscopy to resolve subwavelength features of an object and collect the related local spectral data makes it suitable for various applications where THz spectral imaging on the ∼10–100 μm scale is required.