Magneto-optical Faraday effect is the rotation of polarization plane of linearly polarized light by a magnetic medium. This rotation is caused by magnetic circular birefringence. The Faraday effect can be significantly enhanced by multiple interference because of its non-reciprocity, for example in photonic crystals and microcavities[1,2]. Slow light with a remarkably low group velocity at photonic band-gap edge in photonic-crystal devices was also experimentally demonstrated[3]. Nonmonotonic time dependence of magneto-optical Faraday effect in magnetophotonic crystals at photonic band-gap edge is expected. In this paper nonmonotonic time dependence of magneto-optical Faraday effect in thin Bi:YIG films is observed.The intensity cross-correlation scheme is used for measurements. A femtosecond fiber laser with 70-MHz repetition rate, average intensity of 130 mW, wavelength of 1,55 μm, pulse duration of 130 fs is used as a sourse of radiation. A Glan prism splits an incoming laser pulse into two orthogonally polarized pulses. One of them goes through the sample placed in 208-Hz modulated magnetic field with 110 Oe amplitude. The sample studied is a thin 3-μm thick Bi:YIG film on a 200-μm thick GGG substrate. The difference in optical paths and thus the relative time shift of the pulses can be adjusted by the variable delay. The pulses go through a 45-degreesorientated Glan prism. Both pulses are then focused at the same spot into a crystal with a χ(2) nonlinearity. If the difference in paths is small enough, so that the pulses overlap in time and space at the nonlinear crystal, the noncollinear second-harmonic generation occurs. Its intensity, which is proportional to the pulse crosscorrelation function is detected by a photodiode at a magnetic field frequency as a function of the time delay. Fig.1a shows autocorrelation function of the laser pulse. It is fitted with Gaussian lineshape. The line-width is appeared to be of 160 fs that corresponds to 113-fs pulse duration. Cross-correlation function (Fig.1b) of the pulses without magnetic field applied shows 1650-fs shift, 240-fs width and asymmetric shape. The shift is explained by additional optical pass inside the substrate. The broadening is caused by dispersion of the medium. The shape changes (shoulder on the right-hand side) are associated with multiple interference in the sample. Cross-correlation function shows additional 30-fs shift, 385-fs broadening and more modified shape (relative increase of the shoulder) with magnetic field applied. Change of shape means the nonmonotonic time dependence of Faraday effect.figureFig.1 Intensity autocorrelation of laser pulse (a) and cross-correlation in Bi:YIG films (b) with and without magnetic field