%0 Generic
%A Giordano, MC
%A Viti, L
%A Mitrofanov, O
%A Scamarcio, G
%A Mastel, S
%A Hillenbrand, R
%A Ercolani, D
%A Sorba, L
%A Vitiello, MS
%C Bellingham (WA), USA
%D 2018
%E Razeghi, M
%E Brown, GJ
%E Lewis, JS
%E Leo, G
%F discovery:10060151
%I SPIE
%K Terahertz radiation, Near field, Near field optics, Quantum cascade lasers, Signal detection, Sensors, Spatial resolution
%T Sub-wavelength near field imaging techniques at terahertz frequencies
%U https://discovery.ucl.ac.uk/id/eprint/10060151/
%V 10540
%X Near-field imaging techniques at terahertz (THz) frequencies are severely restricted by diffraction. To date, different detection schemes have been developed, based either on sub-wavelength metallic apertures or on sharp metallic tips. However high-resolution THz imaging, so far, has been relying predominantly on detection techniques that require either an ultrafast laser or a cryogenically-cooled THz detector, at the expenses of a lack of sensitivity when high resolution levels are needed. Here, we demonstrate two novel near-field THz imaging techniques able to combine strongly sub-wavelength spatial resolution with highly sensitive amplitude and phase detection capability. The first technique exploits an interferometric optical setup based on a THz quantum cascade laser (QCL) and on a near-field probe nanodetector, operating at room temperature. By performing phase-sensitive imaging of THz intensity patterns we demonstrate the potential of our novel architecture for coherent imaging with sub-wavelength spatial resolution improved up to 17 μm. The second technique is a detector-less s-SNOM system, exploiting a THz QCL as source and detector simultaneously. This approach enables amplitude- and phase-sensitive imaging by self-mixing interferometry with spatial resolution of 60-70 nm.
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