Phase-sensitive terahertz imaging using room-temperature near-field nanodetectors

Maria C Giordano,Oleg Mitrofanov,Miriam S Vitiello,Leonardo Viti

doi:10.1364/optica.5.000651

Maria C Giordano, Oleg Mitrofanov + Show 2 more

Open Access

https://doi.org/10.1364/optica.5.000651

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Abstract

Imaging applications in the terahertz (THz) frequency range are severely restricted by diffraction. Near-field scanning probe microscopy is commonly employed to enable mapping of the THz electromagnetic fields with sub-wavelength spatial resolution, allowing intriguing scientific phenomena to be explored, such as charge carrier dynamics in nanostructures and THz plasmon-polaritons in novel 2D materials and devices. High-resolution THz imaging, so far, has relied predominantly on THz detection techniques that require either an ultrafast laser or a cryogenically cooled THz detector. Here, we demonstrate coherent near-field imaging in the THz frequency range using a room-temperature nanodetector embedded in the aperture of a near-field probe, and an interferometric optical setup driven by a THz quantum cascade laser. By performing phase-sensitive imaging of strongly confined THz fields created by plasmonic focusing, we demonstrate the potential of our novel architecture for high-sensitivity coherent THz imaging with sub-wavelength spatial resolution.

Highlights

Sub-wavelength resolution near-field imaging techniques in the infrared (IR) and terahertz (THz) ranges have recently shown incredible potential in a variety of application fields ranging from fundamental light–matter interaction studies in nanostructures [1,2,3,4,5] to biological and chemical sciences [6,7,8,9], where highsensitivity combined with non-invasive sub-wavelength probing is required
In aperture-type microscopy, spatial resolution is determined by the aperture size, a; the possibility to achieve resolution smaller than 1/100 of the wavelength is practically limited by strong suppression of aperture transmission T, which follows the power law T ∼ a6 [32,33]
We demonstrated interferometric THz near-field imaging with sub-wavelength spatial resolution using a THz a-SNOM probe with a monolithically embedded coherent detector

Summary

Introduction

Sub-wavelength resolution near-field imaging techniques in the infrared (IR) and terahertz (THz) ranges have recently shown incredible potential in a variety of application fields ranging from fundamental light–matter interaction studies in nanostructures [1,2,3,4,5] to biological and chemical sciences [6,7,8,9], where highsensitivity combined with non-invasive sub-wavelength probing is required. Different near-field probing schemes have been developed and implemented for imaging systems [13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28], exploiting either scattering tip probes (known as apertureless probes) [23,24,25,26,27,28] for achieving nanometer-level resolution, or sub-wavelength size metallic aperture probes (a-SNOM) [14,15,16,22], electro-optic probes [18,20], and miniaturized photoconductive detectors [13,19] The latter approaches are highly versatile and robust for large-scale (100 μm–3 mm scale) near-field sub-wavelength resolution THz microscopy and spectroscopy, and they have enabled investigations of macroscopic THz devices The same interferometric setup enables spectral analysis of the THz field

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