Photoconductive Meta‐Antenna Enabling Terahertz Amplitude Spectrum Manipulation

Abstract

In recent years, as a promising new method, integrating nanostructures to improve the power of photoconductive antennas has received widespread attention. However, there are few reports on the application of artificial electromagnetic structures to regulate the spectral features of photoconductive antennas. Herein, it is demonstrated that by integrating split‐ring resonator (SRR)‐like metallic structures onto the coplanar lines of the photoconductive antenna transmitter, one can significantly manipulate the spectral feature of the generated terahertz (THz) radiation. The guided THz wave along the coplanar lines is scattered by the SRRs to the far field and interferes with the THz pulse radiated from the photoconductive antenna gap, leading to enhancement of the photoconductive antenna's energy and modulation in the spectrum. Further studies have shown that the strength, frequency, and band‐pass/band‐stop characteristics of the modulation can be altered by changing the geometry and placement of the SRRs. Water vapor absorption is also discussed to exemplify the benefit of this novel meta‐antenna over the ordinary photoconductive antenna in sensing scenario. The photoconductive antenna proposed here takes the lead in using artificial structures to manipulate the spectral domain behavior of photoconductive antennas, which is of great significance for THz spectroscopy, imaging, and sensing.

Generation of Tunable Terahertz Waves from Tailored Versatile Spintronic Meta-Antenna Arrays

“…On the contrary, the maximum amplitude of the SMA device in the bandpass band is 2.7 at 0.6 THz, which is 1.63 times higher than the amplitude maximum of the SMA–Slotline device. As demonstrated in the photoconductive meta-antenna by Shi et al, the size of the metamaterial structure has a direct impact on the peak at the resonant frequency, with the distance d (refer to Supporting Information S6) between the spintronic heterostructure and the SRR structures being the most critical parameter. As the distance d increases, the time-domain signal transitions from an initial overlapping of the sub-pulse and main pulse to the separation of the two pulses.…”

“…The sample preparation procedure is reviewed in Supporting Information S3. As pointed out in the study by Shi and Khiabani, when a femtosecond light pulse excites the spintronic films in the middle of the Au blocks, the generated THz waves are coupled not only to free space as far-field radiation but also to the coplanar metamaterials and the substrate planar waveguide. Owing to antenna effects and charge currents, the spintronic terahertz waves coupled into the metallic structure accumulate phase and amplitude in perpendicular directions.…”

“…Some of these devices achieve terahertz polarization manipulation through spin-charge currents and current confinement effects, 13,20 while others enhance terahertz pulses through antenna-coupling effects. [21][22][23][24][25]45 However, the aforementioned spintronic terahertz devices so far have only focused on implementing certain modulations, 26,27 and it still attracts a great interest to develop spintronic terahertz devices with multiple modulation modes. 28 To expand the functionality of spintronic terahertz devices, the integration of emerging terahertz metasurfaces or metamaterials with STE shows great potential for device multifunctionality and miniaturization.…”

“…These schemes can significantly enhance the emission amplitude and achieve spectral modulation; (2) patterned ferromagnetic heterostructure devices with a high design of freedom and flexible manipulation capabilities, such as stripe-patterned ferromagnetic heterostructures, − ,, subwavelength blocky patterned heterostructures, and nanolayered metallic waveguide structures. − These devices and structures that have been introduced into the spintronic terahertz sources greatly enrich the manipulation capabilities of spintronic terahertz waves. Some of these devices achieve terahertz polarization manipulation through spin-charge currents and current confinement effects, , while others enhance terahertz pulses through antenna-coupling effects. − , However, the aforementioned spintronic terahertz devices so far have only focused on implementing certain modulations, , and it still attracts a great interest to develop spintronic terahertz devices with multiple modulation modes…”

Photonics Empowered Passive Radiative Cooling

“…One particular structure we want to emphasize is metasurface‐based thermal emitters. Metasurfaces [ 37,76–82 ] show unparalleled capabilities on controlling light–mater interaction at the subwavelength scale by a simple array of meta‐atoms, greatly easing the fabrication complexity compared with their counterpart metamaterials. Structures, such as plasmonic perfect absorbers [ 83–91 ] and all‐dielectric absorbers, [ 92 ] can be optimized for achieving selective emitters by machine learning methods.…”