Terahertz Cherenkov radiation from ultrafast magnetization in terbium gallium garnet

Abstract

We report an experimental observation of terahertz Cherenkov radiation from a moving magnetic moment produced in terbium gallium garnet by a circularly polarized femtosecond laser pulse via the inverse Faraday effect. Contrary to some existing theoretical predictions, the polarity of the observed radiation unambiguously demonstrates the paramagnetic, rather than diamagnetic, nature of the ultrafast inverse Faraday effect. From measurements of the radiation field, the Verdet constant in the subpicosecond regime is ∼3-10 times smaller than its table quasistatic value.

Cherenkov-type terahertz emission from ultrafast magnetization in a slab of magnetooptic material

“…The pump laser pulse propagated in the TGG slab along its interface with LN and emitted terahertz Cherenkov radiation to the Si-prism outcoupler (the thin layer of LN was used for calibration). The experiment [24] demonstrated the paramagnetic nature of the ultrafast IFE in TGG, contrary to some theoretical expectations [13]. The measured Verdet constant of TGG in the ultrafast regime was in a striking contrast with the results of the optical pump-probe measurements [13] (see also erratum [25]).…”

“…The proposed concept was recently implemented experimentally using a structure with a 35 μm thick layer of lithium niobate (LN) sandwiched between a 2 mm thick slab of terbium-gallium-garnet (TGG) and a Si-prism outcoupler [24]. The pump laser pulse propagated in the TGG slab along its interface with LN and emitted terahertz Cherenkov radiation to the Si-prism outcoupler (the thin layer of LN was used for calibration).…”

Terahertz Radiation by Subpicosecond Magnetization Modulation in the Ferrimagnet LiFe5O8

“…So far, light-induced terahertz radiation has been observed not only in metallic magnets − but also in semiconducting or insulating magnets including diluted magnetic semiconductors and antiferromagnetic insulators. − In metallic magnets such as Ni and permalloy, the magnetic-dipole radiation mechanism is indeed recognized as the dominant process of the terahertz radiation. On the other hand, in an insulating paramagnet, Tb 3 Ga 5 O 12 garnet, , irradiation of a circularly polarized femtosecond laser pulse induces a subpicosecond magnetization modulation via the inverse Faraday effect, which gives rise to light helicity-dependent terahertz radiation. More recently, terahertz radiation originating from the magnetization modulation of Dy 3+ ions via excitations of the f–f electronic transitions was observed in an insulating antiferromagnet DyFeO 3 …”

Terahertz magnetization dynamics induced by femtosecond resonant pumping ofDy3+subsystem in the multisublattice antiferromagnetDyFeO3

“…Finally we would like to note that the strength of the electric field of the broadband THz generation in our experiment reaches 10 V/cm so that the efficiency of the THz generation normalized to the sample thickness is just one order of magnitude smaller than that of ZnTe. However, since the group velocity of the optical pulse in DyFeO 3 is larger than the phase velocity of light at THz frequencies [21,46], a significant enhancement of the emitted THz waves employing the Cherenkov effect [47,48] is quite possible.…”