Terahertz phase imaging and biomedical applications

Terahertz frequency (THz) radiation lies in between the microwave and infrared ranges. While it is strongly absorbed by water, it is nonionizing and has low possibility of causing tissue damage as it involves low energy photons. Recent technological progress in developing THz instrumentation, means that commercial THz systems are being produced with improving performance which are easier to operate and more reliable. THz phase imaging, an advanced imaging technology which combines the benefits of THz and commonly used phase imaging techniques, has recently received significant attention. In this paper, the current state of such imaging systems is reviewed. This review deals with both pulsed and continuous-wave (CW) imaging systems. Pulsed THz phase imaging is a coherent measurement, which includes terahertz pulsed imaging (TPI) based on femtosecond laser and holographic imaging in the time domain, both allow phase and amplitude information of the electric field to be recorded. CW THz phase imaging is mainly based on digital holography, interferometry and ptychography. These systems can obtain the complex amplitude by capturing diffraction patterns and applying numerical reconstruction techniques. Biomedical applications of such THz systems are highlighted.