Continuous-wave terahertz phase imaging using a far-infrared laser interferometer.

Terahertz phase imaging can reveal the depth information of an optically opaque object and provide much better contrast for weak-absorption materials. We demonstrate a continuous-wave terahertz interferometric imaging method in which a far-infrared laser interferometer is used to measure the phase distribution with diffraction-limited lateral resolution and subwavelength axial resolution. An improved four-step phase-shifting algorithm is introduced to retrieve the phase map with very high accuracy and low distortion. The relative depth profiles of two transparent samples are successfully extracted by using this method. Experimental results verify that terahertz interferometric imaging in combination with the phase-shifting technique enables effective reconstruction of the phase image of the object under test.