分类: 光学 >> 量子光学 提交时间: 2023-02-19
摘要: The low-frequency collective excitations, which often occur in the terahertz or multi-terahertz spectral region, play an essential role in many novel emergent phenomena. Despite numerous studies in the bulk, detection of such excitations at interfaces remains challenging owing to the lack of feasible experimental techniques. Here, we show that interfacial low-frequency modes can be characterized using surface-specific nonlinear terahertz spectroscopy. This technique uses intra-pulse difference frequency mixing (DFM) process that can extend the second-order optical spectroscopy to the terahertz range. As a demonstration, the surface phonon of SrTiO3(001) at 2.8 THz was successfully measured. This surface polarization originates from the excess of oxygen vacancies or charge transfer at the interface. We have also developed an analytical procedure for remote measurement of the interfacial potential of complex oxides in a practical environment. Our method offers new opportunities for in situ studies of the low-frequency excitations at interfaces in broad disciplines.
分类: 光学 >> 量子光学 提交时间: 2023-02-19
摘要: Searching multiple types of terahertz (THz) irradiation source is crucial for the THz technology. Here, by utilizing a two-dimensional (2D) ferromagnetic Cr2Ge2Te6 crystal, we firstly demonstrate a magneto-tunable monochromatic THz irradiation source. With a low-photonic-energy broadband THz pump, a strong THz irradiation with frequency ~0.9 THz and bandwidth ~0.25 THz can be generated and its conversion efficiency could even reach 2.1% at 160 K. Moreover, it is intriguing to find that such monochromatic THz irradiation can be efficiently modulated by the magnetic field below 160 K. According to both experimental and theoretical analyses, the emergent THz irradiation is identified as the emission from the phonon-polariton and its temperature and magnetic field dependent behaviors confirmed the large spin-lattice coupling in this 2D ferromagnetic crystal. These observations provide a new route for the creation of tunable monochromatic THz source which may have great practical interests in future applications in photonic and spintronic devices.