Abstract
High-speed terahertz (THz) reflection three-dimensional (3D) imaging is demonstrated using electronically-controlled optical sampling (ECOPS) and beam steering. ECOPS measurement is used for scanning an axial range of 7.8 mm in free space at 1 kHz scan rate while a transverse range of 100 × 100 mm(2) is scanned using beam steering instead of moving an imaging target. Telecentric f-θ lenses with axial and non-axial symmetry have been developed for beam steering. It is experimentally demonstrated that the non-axially symmetric lens has better characteristics than the axially symmetric lens. The total scan time depends on the number of points in a transverse range. For example, it takes 40 s for 200 × 200 points and 10 s for 100 × 100 points. To demonstrate the application of the imaging technique to nondestructive testing, THz 3D tomographic images of a glass fiber reinforced polymer sample with artificial internal defects have been acquired using the lenses for comparison.
Highlights
Terahertz (THz) tomography can be used for nondestructive testing, due to the transparency of nonconductive materials to THz radiation [1,2,3]
electronically-controlled optical sampling (ECOPS) measurement is used for scanning an axial range of 7.8 mm in free space at 1 kHz scan rate while a transverse range of 100 × 100 mm2 is scanned using beam steering instead of moving an imaging target
Telecentric f-θ lenses with axial and non-axial symmetry have been developed for beam steering
Summary
Terahertz (THz) tomography can be used for nondestructive testing, due to the transparency of nonconductive materials to THz radiation [1,2,3]. For real-time B-scan (one-dimensional transverse scan along with axial scan) imaging or fast three-dimensional (3D) imaging, reflection-mode THz tomography utilizing time-offlight information is more favorable than transmission-mode tomography because the former needs neither rotation for projection angles nor image reconstruction [11,12,13]. We demonstrated high-speed THz reflection 3D imaging by combining electronically-controlled optical sampling (ECOPS) with fast transverse moving of an imaging target using translation stages [14]. While A-scan (axial scan) data were acquired at 1 kHz scan rate using ECOPS measurement of THz time-domain waveforms [15], the total scan time for obtaining a 3D tomographic image was limited by the speed and acceleration of the translation stages. The characteristics of the lenses are demonstrated in the high-speed THz reflection 3D imaging system using beam steering. THz 3D tomographic images of a glass fiber reinforced polymer (GFRP) sample with artificial defects are shown, acquired quickly using the imaging system
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