Extended depth of field in continuous-wave terahertz computed tomography based on Bessel beam

Terahertz (THz) radiation is able to penetrate many different types of nonpolar and nonmetallic materials. THz imaging can be combined with computed tomography (CT) to form THz CT, which is an effective method to visualize the sample's internal structure. Here, we report the continuous-wave (CW) THz CT imaging results using Bessel beam generated by use of axicon. In this method, the sample cross section is scanned in all translation and rotation directions. Due to the non-diffracting property of the Bessel beam, two-dimensional (2-D) cross-sectional images of the internal structure of the plastic pipe at different distances from axicon can be full reconstructed by using filtered back projection algorithm. Compared with conventional Gaussian beam, Bessel beam can extend the depth of field in CW THz CT system. Using this system, we obtained 2-D cross-sectional image of the internal structure of the clogged plastic pipe and the obstruction was accurately detected by comparing 2-D cross-sectional images at different sections. Our experimental data demonstrated a feasible application of the CW THz CT system with Bessel beam in non-destructive testing.