Over the past decade, terahertz electromagnetic waves with sub-millimeter wavelength (30 µm to 3 mm) have attracted much attention due to the wide range of applications in medical and industrial fields. Magnetic thin film heterostructures (spintronic emitters) consisting of ferromagnet and nonmagnetic metal layers have recently emerged as broadband THz sources that may have advantages over conventional sources such as photoconductive antennas (PCA) and nonlinear crystals. Here, we demonstrate how to use spintronic emitters patterned into microstructures of different geometries and dimensions to modify the characteristic electromagnetic spectrum of the emitted THz waves. Furthermore, we theoretically explore the possibility of combining emergent spintronic emitters with conventional PCA as hybrid emitters for THz pulse shaping and controlling the handedness of the polarization of THz waves. This new method takes advantage of the broad bandwidth of spintronic emitters and high-intensity THz emission at the low frequency of PCAs. These modelings are confirmed by preliminary experiments. Our results are beneficial to the production of functional THz devices with tunable parameters.
Strain engineering of the two-dimensional semiconductor gallium selenide has recently revealed exciting nanophotonic effects such as localized bandgap tuning, exciton funneling, and the creation of site-specific single photon emitters. We investigate the reversible local strain engineering of suspended gallium selenide flakes by using a novel micromechanical spring with nanoscale probes for inducing symmetry-controlled localized strain. By performing strain engineering measurements on suspended gallium selenide flakes as opposed to using patterned substrates, unintended strain originating from the surrounding environment is avoided. Our results show that gallium selenide undergoes a reversible bandgap redshift of >6 meV. The presented research establishes a new platform for streamlining the quantitative understanding of material properties as a function of complex local strain in two-dimensional materials for quantum photonics applications.
Dynamic THz modulations with adaptive metamaterials have been demonstrated. By utilizing the significant volume shrinkage during the phase-transition of phase-transition materials, a specially designed chiral structure performs drastically structural deformation. The rapid geometrical change modulating the polarization of the incident THz wave is fully designable, continuously tunable, and reversible. Large azimuth rotation angle and ellipticity angle changes have been observed. The metamaterials are actuated by either global heating or Joule heating, providing an efficient way to modulate THz waves with high modulation depth. This brings us a prosperous future of broader THz applications such as radar, communications, and imaging systems.
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