A terahertz confocal microscope for far-field thermal radiation detection and near-field sub-wavelength imaging

Qianchun Weng; Le Yang; Jie Xu; Qingbai Qian; Haochi Yu; Bo Zhang; Zhenghua An; Ziqiang Zhu; Wei Lu

doi:10.1117/12.2212029

5 November 2015 A terahertz confocal microscope for far-field thermal radiation detection and near-field sub-wavelength imaging

Qianchun Weng, Le Yang, Jie Xu, Qingbai Qian, Haochi Yu, Bo Zhang, Zhenghua An, Ziqiang Zhu, Wei Lu

Author Affiliations +

Proceedings Volume 9795, Selected Papers of the Photoelectronic Technology Committee Conferences held June–July 2015; 97950U (2015) https://doi.org/10.1117/12.2212029
Event: Selected Proceedings of the Photoelectronic Technology Committee Conferences held June-July 2015, 2015, Hefei, Suzhou, and Harbin, China

Abstract

We present a novel scattering-type scanning near-field optical microscope (s-SNOM) operating in the terahertz (THz) wavelength. A home-made ultra-high sensitive detector named charge sensitive infrared phototransistor (CSIP, detection wavelength ~15 μm) is equipped for spontaneous thermal radiation detection (external illumination should be avoided). Thermal emission from room-temperature objects is collected by a cassegrain objective lens placed above the sample, and focused to a pinhole (d=250 μm) which is kept in liquid-helium (LHe) temperature(4.2 K). With the background radiation from environment efficiently blocked by the low-temperature pinhole, the detector is only sensitive to the THz radiation from a small spot (~λ) on sample surface (the confocal point). As a result, thermal radiation spontaneously emitted by object itself is measured with an excellent spatial resolution of ~14 μm (diffraction-limit). For overcoming the diffraction limit by detecting the near-field evanescent waves, this THz microscope is combined with a home-built atomic-force microscope (AFM). With sharp AFM tip (<100 nm) scattering the evanescent waves with an improved tip-modulation method, we successfully obtained thermal near-field images with a spatial resolution of ~100 nm, which is already less than 1% of the detection wavelength (15 μm). This THz s-SNOM should be a powerful tool for various material research down to the nanometer scale.

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Qianchun Weng, Le Yang, Jie Xu, Qingbai Qian, Haochi Yu, Bo Zhang, Zhenghua An, Ziqiang Zhu, and Wei Lu "A terahertz confocal microscope for far-field thermal radiation detection and near-field sub-wavelength imaging", Proc. SPIE 9795, Selected Papers of the Photoelectronic Technology Committee Conferences held June–July 2015, 97950U (5 November 2015); https://doi.org/10.1117/12.2212029

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KEYWORDS

Terahertz radiation

Near field

Microscopes

Sensors

Confocal microscopy

Spatial resolution

Modulation

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