Broadband Spintronic Terahertz Emitter with Magnetic‐Field Manipulated Polarizations

Abstract

0.1-30 THz) have experienced an unprecedentedly rapid progress with potential in fundamental sciences and real applications, especially under the fast development of ultrafast laser technology. [1] Recently, terahertz technologies have also been successfully employed in laboratories as powerful tools for triggering other novel related researches and applications, such as electron accelerations, [2] strong-field nonlinear phononics, [3] nonlinear terahertz photonics, [4] nonionization imaging, [5] and so on. Significantly large potential of terahertz technology could be envisaged in its real applications such as nondestructive spectroscopy [6] and ionization-free imaging, highly sensitive sensing, [7] short-range wireless communication at terahertz bit rates, [8,9] and so on. However, hindering the development of this fascinating technology from real applications lies in the lack of highly efficient terahertz sources, versatile functional devices, and sensitive detectors, as well as compact and robust systems. Among them, terahertz sources are significantly important, especially for those integrated with flexible manipulation of terahertz polarization states. As well demonstrated, when carrying with optical spin and angular momentum, [10] it enables another freedom of utilizing terahertz waves and boosts Flexible manipulation of terahertz wave polarizations during the generation process is very important for terahertz applications, especially for the next-generation on-chip functional terahertz sources. However, current terahertz emitters cannot satisfy such demand, hence calling for new mechanisms and conceptually new terahertz sources. Here an efficient and broadband terahertz source with magnetic-field-controlled flexible switching for the polarizations between linear and elliptical states in ferromagnetic heterostructures driven by femtosecond laser pulses is demonstrated. More importantly, the chirality, azimuthal angle, and ellipticity of the generated elliptical terahertz wave can be precisely manipulated by harnessing external magnetic fields via effectively tailoring the photoinduced spin currents. Such an ultrafast photomagnetic interaction-based, magnetic-field-controlled, and broadband tunable solid-state terahertz source integrated with polarization tunability functions not only provides the capability to reveal physical mechanisms of femtosecond spin dynamics, but also demonstrates the feasibility to realize novel on-chip terahertz functional devices, boosting the potential applications for controlling elementary molecular rotations, phonon vibrations, spin precessions, high-speed communications, and accelerating the development of ultrafast terahertz optospintronics. Terahertz RadiationThe ORCID identification number(s) for the author(s) of this article can be found under https://doi.

Generation and manipulation of chiral terahertz waves in the three-dimensional topological insulator Bi2Te3

“…Between the second and third parabolic mirrors, there were two terahertz polarizers inserted into the optical path to resolve the terahertz polarization. 19 The optical path from the terahertz emitter to the detector was sealed and pumped to eliminate the influence of water vapor. All of the experiments were carried out at room temperature.…”

“…Currently, there are already several such kinds of vector-manipulated polarized terahertz sources. [17][18][19][20][21] For example, femtosecond laser amplifier pumped air plasma, when intensively tuning the phase delay and the pump pulse polarization between two different pump pulse colors, can enable the opportunity to obtain arbitrarily shaped terahertz polarizations. 17 Furthermore, terahertz polarization pulse shaping with arbitrary field control has also been demonstrated by optical rectification of a laser pulse whose instantaneous intensity and polarization state are flexibly controlled by an optical pulse shaper.…”

“…18 Recently, elliptically and circularly polarized terahertz waves have been realized in W/CoFeB/Pt heterostructures through deliberately engineering the applied magnetic-field distribution and the cascade emission method, respectively. 19,20 In a NiO single crystal, double-pulse excitation has also been used to vectorially control magnetization by radiating spin-polarized terahertz waves, 21 in which an electron spin-polarized wave (magnon oscillation) has been purposely vectorially controlled and manipulated. In addition, highly efficient chiral terahertz emission with elliptical polarization states has been obtained from the fascinating topological phase matter, bulk Weyl semimetal TaAs with reflection terahertz emission geometry.…”

Active Tunable THz Metamaterial Array Implemented in CMOS Technology

“…The THz experiments were performed on a home-built THz time-domain spectrometer ( Fig. 5a) driven by a commercial Ti: sapphire laser oscillator, which is consistent with the system used in reference [14]. The center wavelength of the femtosecond laser pulses was 800 nm, the pulse duration was 70 fs, and the repetition frequency was 80 MHz.…”

“…Two other parabolic mirrors were then used to collimate and focus the transmitted THz waves onto the ZnTe crystal. The THz electric field can induce the variation of the refractive index of the detected crystal, which is coherently recorded by electro-optic sampling method through the ZnTe crystal, a /4 wave-plate, a Wollaston prism and a pair of photodiodes [14]. All the measurements were carried out under dry nitrogen gas environment to eliminate the fluence from water vapor.…”