CC BY
1The 30th International Conference on Advanced Laser Technologies N-I-5
ALT'23
Controlling the polarization of THz radiation in spintron emitters
E. Mishina
MIREA - Russian Technological University, Vernadsky ave. 78, Moscow, Russia 119454
mishina_elena5 7@mail.ru
The generation of terahertz (THz) radiation is of great technological importance for many applications, such as non-destructive diagnostics, ultrafast computing, wireless communication, and direct control of material order parameters. Over the past decade, a lot of work has been done to find materials and mechanisms that provide terahertz radiation with the required characteristics. Spintron structures as terahertz emitters (SHEs) have special characteristics. First of all, this is a wide spectral range of radiation (0.5 ^ 15 THz, two orders of magnitude of the dynamic range) with a signal amplitude comparable to that of a reference emitter, a ZnTe crystal. THz radiation is excited in the SHE by a femtosecond laser pulse due to the mechanism of the inverse spin Hall effect, where the ultrafast spin new photocurrent is converted into a transverse charge current. The highest efficiency of conversion to THz radiation was achieved with SHE in bi- and three-layer structures based on Co/Pt [1]. Polarization of THz radiation in SHE is perpendicular to its magnetization.
To work with THz radiation, as well as with optical, elements of THz optics are required, in particular, polarization rotators (analogues of a half-wave plate). The obvious way to rotate the polarization of the THz wave is to rotate the magnet around the SHE, which is extremely inconvenient. In this paper, we show the ways of polarization rotation upon changing only the magnitude of the external magnetic field in the spintron emitter and the magnitude of the voltage in the spintron emitter/piezoelectric structure.
Rotation of the plane of polarization without rotation of the magnet, but only by changing the strength of the external magnetic field, is possible in materials with a spin-reorientation transition (SRT) induced by a magnetic field. To do this, the structure must have an anisotropy of the "easy axis" type. In voltage controlled systems, energy consumption is usually lower than with current control. The use of a composite mul-tiferroic is a way to combine the advantages of SHE and voltage control. The main problem of controlled spintron emitters is their low efficiency. In structures based on Co/Pt, which have the highest THz conversion efficiency, polarization control has not yet been demonstrated.
In this paper, a short review of current situation with achievments on THz emitters will be presented, both commonly used and polarization controlled ones. New results on magnetic-field controlled spintromic emitters will be shown.
The work is supported by Russian Science Foundation (Grant№ 23-19-00849).
[1] T. Seifert, S. Jaiswal, U.Martens, et al, Efficient metallic spintronic emitters of ultrabroadband terahertz radiation, Nature Phot. vol.10, pp. 483-488, (2016).
