Terahertz confocal imaging: Polarization and sectioning characteristics

The development of high-resolution THz imaging systems is currently of great practical significance, (e.g. in the areas of security, agri-food, biomedicine etc.). Implementing and calibrating such systems is essential, as is the verification and appropriate use of models. Confocal microscopes are well known to improve resolution and provide 3D images. In this paper a novel terahertz (THz) confocal transmission scanning microscopy is implemented using a commercial 300 GHz (similar to 1 mm) electronic THz source and sensor array. In order to calibrate the system, two objects, a high contrast amplitude metallic object and a low contrast surface relief phase pattern, are produced. These simple samples are imaged to quantify the polarization and sectioning properties of the imaging system. A scalar model is shown to be appropriate and is shown to predict the measured lateral and axial resolutions. Experimental results using two more complex objects are then presented, confirming confocal operation. This paper details the implementation and calibration of a 3D THz confocal imaging system.