ИСТИНА

Faraday effect is a phenomenon widely used for light propagation control. The effect is non-reciprocal and proportional to the thickness of a magnetic medium. Thus, it can be enhanced in multilayered structures with artificial dispersion and group delay, such as magnetophotonic crystals. In case of short femtosecond laser pulse its front part interacts with the structure less effectively than the rear one, so the latter one should rotate stronger and, due to that, Faraday rotation will grow with time. Until now, however, ultrafast dynamics of magneto-optical effects has always been connected with magnetization changes. The goal of the work is to demonstrate Faraday effect evolution caused by the pulse interference in the layered structure. To detect the time dependence of Faraday rotation autocorrelation technique has been used. We measured autocorrelation function of the 130-fs laser pulse with tunable central wavelength, which passed through magneto-photonic crystal (a Bi:YIG cavity spacer between two dielectric Bragg reflectors consisting of 5 pairs of SiO2 /Ta2O5 layers) with the center of microcavity mode at the 895 nm. Fig. 1 shows measured femtosecond dynamics of the Faraday rotation in the sample with changing central wavelength of a laser pulse in the vicinity of the microcavity mode. The spectral profile gets sharper with time, since the pulse superposes with itself more effectively in the center of microcavity mode. In other words, the closer pulse central wavelength to the center of the microcavity mode, the stronger is the growth with time. To conclude, ultrafast Faraday rotation dynamics in a magnetophotonic microcavity has been detected. It is caused by the pulse self-interference inside its layers. The character of dynamics strongly depends on spectral position of the pulse central wavelength due to the strong artificial dispersion of the medium. The time derivative of Faraday rotation is the greatest when pulse central wavelength is at the center of microcavity mode and much less when it’s in the vicinity of this point. [1] A.V. Chetvertukhin et al., J. Appl. Phys., 111 (2012) 07A944. [2] A.I. Musorin et al., Bulletin of the Russian Academy of Sciences: Physics, 78 (2014) 43-48.