Imaging in the terahertz (THz) spectral range is a valuable screening tool. However, the quality of sources, detectors and refractive elements lags significantly behind their optical counterparts. Furthermore, owing to the long wavelength of THz waves, the corresponding diffraction-limited resolution extends to the sub‑millimetre scale, far exceeding that of optical and infrared systems. This leads to an unfavourable trade-off between the field of view and achievable spatial resolution of THz imaging.
In Fourier ptychographic imaging, the sample is scanned under a range of illumination angles, and the collected transmission images are digitally processed to restore the structural information beyond the diffraction limit. “The motorized kinematic mirror provides controlled angular steering of the incident THz beam, effectively generating a sequence of plane-wave illuminations from different directions. Each tilt corresponds to a shifted region in the object’s Fourier spectrum,” explained Kumar. “By precisely controlling the mirror with sub-degree angular steps, the experiment captures many illumination angles, enabling synthetic aperture formation and accurate reconstruction of high spatial frequencies.”