Terahertz confocal microscopy with a quantum cascade laser source.

We report on the implementation of a confocal microscopy system based on a 2.9 THz quantum cascade laser source. Lateral and axial resolutions better than 70 µm and 400 µm, respectively, are achieved, with a large contrast enhancement compared to the non-confocal arrangement. The capability of resolving overlapping objects lying on different longitudinal planes is also clearly demonstrated.