# Full-Field Super-Resolution Terahertz Imaging Based on Rotating Coherent Scattering Microscopy
###### Abstract  
For decades, terahertz (THz) microscopic imaging has been limited by the resolution of the system due to the larger wavelength, the power of the source, and the equivalent noise power of the detector, so a lot of research has focused on single-point scanning imaging. With the development of hardware, full-field THz imaging based on high-power continuous-wave THz sources have been developed such as the direct intensity imaging method and lensless coherent imaging. In particular, the THz direct intensity imaging method requires no complicated computational reconstruction, while the high resolution, as a key issue, still needs to be improved. In this paper, the rotating coherent scattering microscopy was applied to THz imaging for the first time. Here, we designed and fabricated a hemisphere lens with high-resistance silicon. The tilted hemisphere lens transformed the incident divergent beam into a plane wave, and the total internal reflection occurred in the planar surface within the hemispherical lens, and generated evanescent waves in the rare medium. At the same time, the sample was placed very close to the plane of the hemispherical lens, so that the sample was illuminated by the evanescent waves. The scattered waves carried high frequency information to the far field, and thus through an objective, the super-resolution imaging was achieved along a single direction. Then, the hemispherical lens was rotated to obtain coherent scattering microscopic images under different evanescent wave illumination angles. Finally, the full-field super-resolution imaging results were obtained through incoherent superposition. t 1 20232002331 1 98220023 12 98220023 12 9820023 12  
used to form a focused spot with a subwavelength size. For PW THz, scattering media are used in wavefront shading to spatio-temporal focusing for THz optical correction systems [15] and ghost imaging [16]. Then, super-resolution imaging can be achieved by scanning the sample point by point by using the focused spot as the illumination beam. Because of the high transmittance and high refractive index of silicon and high resistivity float zone silicon (HRZF-Si) in the THz band, the solid immersion lens is used for point-scanning imaging [17; 18; 19]. When a dielectric particle of wavelength magnitude is placed in the terahertz wave focus position, a terajet beyond the diffraction limit can be generated, significantly improving the spatial resolution of the terahertz imaging system [20]. In particular, it is easy to generate photonic hooks due to the asymmetry of mesoscale dielectric particle structures such as cylinder, half-cylinder, and cubic particle [21]. In addition to the factor of the imaging resolution, the main reason preventing the wide application of THz imaging is the slow acquisition time of the conventional point-scanning method, and the high-power requirement of the source for the THz full-field imaging. With the development of high-power CW and PW THz sources such as gas lasers, cavity-based photoconductive sources [22], and high-sensitivity area array detectors such as pyroelectric detectors and microbolometers, full-field imaging has become possible. However, the problem of low imaging resolution caused by the long wavelength still exists. In recent years, the full-field CW-THz imaging technology includes the phase-contrast imaging methods [1; 23] and the direct intensity imaging methods. The former is represented by digital holography [24; 25], ptychography [26; 27; 28], and transport-of-intensity equation (TIE) imaging [29]. In these methods, two-dimensional (2D) photosensitive elements are used to record the interference or diffraction pattern of the samples under the THz illumination, and various reconstruction algorithms have been proposed to retrieve the distribution of the complex electromagnetic field in the sample plane. The latter makes use of the parabolic reflectors/spherical lenses or the lens sets.