Printing special surface components for THz 2D and 3D imaging

Bo Yan,Lie Lin,Xing Zhao,Xiaolei Wang,Weiwei Liu,Zhigang Wang,Cheng Gong

doi:10.1038/s41598-020-77998-9

Bo Yan, Lie Lin + Show 5 more

Open Access

https://doi.org/10.1038/s41598-020-77998-9

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Abstract

The paper reports an off-axis large focal depth THz imaging system which consists of three 3D printed special surface components (two aspherical mirrors and an axicon). Firstly, the optical design software is used to design and optimize the aspherical parabolic mirror. Secondly, the optimized mirror is prepared by a 3D printing and metal cladding method. Thirdly, a THz axicon is designed for generation of quasi-Bessel Beam and a new geometric theoretical model of oblique incident light for axicon is established. Finally, the imaging system based on the special surface components is constructed. Its maximum diffraction-free distance is about 60 mm, which is 6 times higher than the traditional system. To verify the effectiveness, THz two-dimensional imaging experiments and three-dimensional computed tomography experiment are carried out. The results are consistent with the design and calculations.

Highlights

Recent years, terahertz (THz) wave shows tremendous potential in the fields of nondestructive testing, imaging and communications due to its excellent properties
Since transverse intensity distribution does not change with propagation distance, the Bessel beams exhibit non-diffracting property in free space, which can be utilized to extend the focal depth of imaging systems
In this paper, aiming at the off-axis large focal depth THz imaging based on printed special surface components, the design and fabrication of aspherical parabolic mirror and axicon are introduced

Summary

Design and theory

The proposed THz imaging system consists of an axicon and two aspherical mirrors. According to the design principle from simple to complex, we first introduce the simplified aspherical imaging system without axicons. The parabolic mirror 1 is the same as the mirror 2 Their initial design parameters are as follows: The wavelength is 3173um, the diameter is 50 mm, and the light turning angle is 60 degrees. It can be seen that the geometric radius of the focusing spot of aspheric surface can reach 2838.18 μm after optimization, while that of standard surface is about 3861.42 μm. Comparison of focusing effect after optimization: aspheric surface and standard surface. According to the law of refraction and geometric relation, the angle α between the light passing through the axicon and the horizontal line can be calculated by:.

Experiments and results

Conclusion

Method