Optimization and applications of air-plasma dynamic aperture-based terahertz microscopy

Terahertz (THz) microscopy has become an important far-infrared inspection method because it possesses a high spatial resolution and retains THz spectral information. For further exploiting applications of THz microscopy, we propose an air-plasma dynamic aperture-based THz near-field technique to achieve sub-wavelength THz imaging without approaching a sample surface. In this work, the measurement mode of the technique was improved and a corresponding data processing method was applied to upgrade the system performances. By utilizing the proposed method, the measurement time was reduced about 4 times and the signal-to-noise ratio of the system was enhanced more than 6 times compared to the previous one. Utilizing the superiorities of the system, three unique application functions were demonstrated, including imaging of isolated objects, identifying semifluid chemicals, and characterizing a semifluid surface. The work effectively promoted the maturation of the imaging technique and greatly broadened the applications of THz microscopy in fundamental research and industrial inspection.