Single optical element to generate a meter-scale THz diffraction-free beam

• Published in: Optics express Vol. 30; no. 22; pp. 39976 - 39984
• Main Authors: Tu, Siyu, Peng, Jinyu, Yang, Zhengang, Liu, Jinsong, Wang, Kejia
• Format: Journal Article
• Language: English
• Published: 24.10.2022
• ISSN: 1094-4087; 1094-4087
• DOI: 10.1364/OE.471070

Diffraction-free electromagnetic beam propagates in free space without change in its two-dimensional transverse profile. Elongating diffraction-free length can benefit the practical application of this beam. Here, we demonstrate that a THz diffraction-free beam with meter-scale length can be achieved by using only one optical element. By circumscribing the line-shape of spherical harmonic function on a traditional axicon, such optical element is designed, and then can be fabricated by 3D-printing technique. Simulated, experimental, and theoretical results all show that the diffraction-free length of generated beam is over 1000 mm. Further analysis based on Fourier optics theory indicates that the spatial frequency of this beam has a comb distribution, which plays a key role during the beam generation process. Moreover, such distribution also demonstrates the beam generated by our invented optical element is not the Bessel beam, but a new diffraction-free beam. It is believed that this meter-scale THz diffraction-free beam can be useful in a non-contact and non-destructive THz imaging system for large objects.