Real-time two-dimensional terahertz tomography of moving objects

We propose real-time two-dimensional (2D) terahertz (THz) tomography for 2D cross-sectional imaging of moving objects. The proposed method does not require mechanical scanning elements for time delay and sample position, which are essential for conventional THz tomography. For this purpose, a 2D spatiotemporal THz image is acquired at a frame rate of 10 frame/s by a combination of time-to-space conversion using non-collinear 2D free-space electro-optic sampling and line focusing of a THz beam on a sample. We demonstrate the use of real-time 2D THz tomography for real-time monitoring of the paint thickness in a moving paint sample and the drying progress in a wet paint film. The proposed method provides a powerful tool for non-ionizing and non-contact probing in the fields of nondestructive testing and biomedical diagnostics.