Interference fringes are quite common in coherent imaging systems. As a kind of waves, terahertz (THz) light has such a phenomenon inherently when multiple reflections happen in focal plane imaging systems, which generally includes several mirrors. In this paper, we will demonstrate the fringe pattern in a typical reflective imaging system, which is similar to the Newton Ring phenomenon as in optics. The good point is that it might be helpful to measure the gesture of the object, while it is quite annoying in imaging since important information is hidden behind the fringes and we could even not recognize the object. To obtain a decent image, we propose three methods via tuning the frequency and location of the objects, also we can tune the illumination angle of THz waves.

This work was published on MICROWAVE AND OPTICAL TECHNOLOGY LETTERS,2018,60(10):2492-2496. Origin of interference fringes and its countermeasures in coherent terahertz imaging.