Vortex beams have received considerable research interests both in optical and millimeter-wave domain since its potential to be utilized in the wireless communications and novel imaging systems. Many well-known optical beams have been demonstrated to carry orbital angular momentum (OAM), such as Laguerre-Gaussian beams and high-order Bessel beams. Recently, the radially symmetric Airy beams that exhibit an abruptly autofocusing feature are also demonstrated to be capable of carrying OAM in the optical domain. However, due to the lack of efficient devices to manipulate terahertz (THz) beams, it could be a challenge to demonstrate the radially symmetric Airy beams in the THz domain. Here we demonstrate the THz circular Airy vortex beams (CAVBs) with a 0.3-THz continuous wave through 3D printing technology. Assisted by the rapidly 3D-printed phase plates, individual OAM states with topological charge l ranging from l = 0 to l = 3 and a multiplexed OAM state are successfully imposed into the radially symmetric Airy beams. We both numerically and experimentally investigate the propagation dynamics of the generated THz CAVBs, and the simulations agree well with the observations.

We present a method to design and fabricate a kind of converters based on flexible metasurfaces which can change the polarization state of an incident terahertz beam. The metasurface consists of a two-dimensional array of rectangular metallic antennas that can abruptly change the phase of the incoming terahertz beam. Experimentally demonstrated half-wave plates generate 0.1 THz beam with a π/2 polarization rotation. By slightly changing the structure of the converter, an elliptically or circularly polarized beam is expected to be obtained. These flexible terahertz converters may have many potential applications in terahertz technology.

We demonstrate a 3D printed diffractive mode transformer to discriminate orbital angular momentum (OAM) modes of terahertz (THz) vortex beam via an optical geometrical transformation method. THz vortex beams with the integer quantum number l ranging from -3 to +3 are detected.

为了研究太赫兹无损检测技术对复合材料与金属板黏合面粘接质量的检测能力,在隔热板上制造了不同特征的人工缺陷,并使用德国SynViewScan 300连续太赫兹波成像系统对样件进行了检测.结果表明,太赫兹波能够穿透复合材料,并获得复合材料与金属板的黏合面处的2维太赫兹图像,从图像中能够清晰地分辨出不同特征的缺陷.该研究结果为检测复合材料黏合质量及脱黏状况提供了有效的办法.

We design a plano-convex lens working in the terahertz (THz) frequency range and fabricate it using three-dimensional (3D) printing technology. A 3D field scanner is used to measure its focal properties, and the results agree well with the numerical simulations. The refractive index and absorption coefficient measurements via THz time-domain spectroscopy (THz-TDS) reveal that the lens material is highly transparent at THz frequencies. It is expected that this inexpensive and rapid 3D printing technology holds promise for making various THz optical elements.

We present the generation of arbitrary order Bessel beams at 0.3 THz through the implementation of suitably designed axicons based on 3D printing technology. The helical axicons, which possess thickness gradients in both radial and azimuthal directions, can convert the incident Gaussian beam into a high-order Bessel beam with spiral phase structure. The evolution of the generated Bessel beams are characterized experimentally with a three-dimensional field scanner. Moreover, the topological charges carried by the high-order Bessel beams are determined by the fork-like interferograms. This 3D-printing-based Bessel beam generation technique is useful not only for THz imaging systems with zero-order Bessel beams but also for future orbital-angular-momentum-based THz free-space communication with higher-order Bessel beams.

By designing and fabricating 3D printed spiral phase plates (SPPs), we demonstrate basic functionalities for terahertz (THz) orbital angular momentum (OAM) communications, including the generation, detection, conversion, multicasting and manipulation of OAM at 0.1 THz.

Terahertz (THz) imaging technology shows great advantage in nondestructive detection (NDT), since many optical opaque materials are transparent to THz waves. In this paper, we design and fabricate dielectric axicons to generate zeroth order-Bessel beams by 3D printing technology. We further present an all-electric THz imaging system using the generated Bessel beams in 100GHz. Resolution targets made of printed circuit board are imaged, and the results clearly show the extended depth of focus of Bessel beam, indicating the promise of Bessel beam for the THz NDT.

Transformation thermodynamics, as one of the important branches among the extensions of transformation optics, has attracted plentiful attentions and interests recently. The result of transformation thermodynamics, or called as "thermal cloak", can realize isothermal region and hide objects from heat. In this paper, we presented the concept of "reverse thermal cloak" to correspond to the thermal cloak and made a simple engineering definition to identify them. By full-wave simulations, we verified that the reverse thermal cloak can concentrate heat and realize local heating. The performance of local heating depends on the anisotropic dispersion of the cloaking layer's thermal conductivity. Three-dimensional finite element simulations demonstrated that the reverse thermal cloak can be used to heat up objects. Besides pre-engineered metamaterials, such reverse thermal cloak can even be realized with homogenous materials by alternating spoke-like structure or Hashin coated-sphere structure.

Terahertz wave carrying OAM would boost the capacity of free-space communication with a high carrier frequency and additional degrees of freedom. In this work, we present a experimental demonstration of THz orbital angular momentum (OAM) encoding via 3D printed spiral phase plates(SPPs). By using four "coding" spps with toplogical values -2,-1,+1,+ 2, we can encode OAM information onto THz waves and generate temporal varying OAM states with controlled sequences (i.e., 2-bit coding). By using interference between OAM beam and a reference gaussian beam, the OAM information can be detected from the interference fork pattern.

We present a proof of concept demonstration of THz free-space communication employing orbital angular momentum (OAM) multiplexing. Two different OAM modes are multiplexed and de-multiplexed in experiment via 3D printed spiral phase plates.