Dynamics of polarization switching is the central problem of ferroelectric-based electro-optical modulators, high-speed nonvolatile ferroelectric random access memories and electro-optical switchers. For these applications polarization has to be reversed not only by electromagnetic wave of GHz range, but also by application of a single short voltage pulse. Investigation of the dynamics of polarization reversal is highly important for optimization of the films parameters with respect to their switching characteristics. In the present paper we report the results of polarization switching in Nd doped BFO (NBFO) thin films and BST/NBFO/BST planar structures studied by second harmonic generation (SHG) technique for different frequencies of applied bias. Heteroepitaxial Bi0.97FeNd0.03O3 films with various thickness were fabricated by high-frequency sputtering on MgO(100) substrate. Epitaxial structure of the films was confirmed by X-ray diffraction. The same method was used for fabrication of BST/NBFO/BST planar structure with the layer thickness of about 20 nm. For electric field application aluminum interdigital electrode system was deposited on the film surface by photolithography, which provides in-plane switching of the ferroelectric polarization during voltage application up to 10 V. The electrode system serves simultaneously as a diffraction grating with a period of ~2 μm and a gap of 1,1 μm (Fig.1). As it was shown earlier [1-2] the SHG is extremely efficient for studying ferroelectric properties. The reason is that in the simplest consideration the SHG field is the linear function of ferroelectric polarization. The dependences of the SHG intensity on the applied electric field can be described by the expression [3]formulawhere E^2w_bg is the incoherent component of unswitchable (independent of the external electric field) part of the second harmonic field; P(E) is the ferroelectric (switchable) polarization, which depends on the external electric field; P0 is the total contribution of the remanent polarization and the coherent component of the unswitchable polarization; and x is the proportionality coefficient which caracterizes the switching efficiency and is determined by the Fresnel factor and the nonlinear susceptibility. Optical SHG was excited by the output of a Ti:sapphire laser at 760 nm with a pulse width of about 100 fs, repetition rate 82 MHz and the pulse power density up to 5·109 W/cm2. Frequency dependencies of the SHG intensity were measured during a ramp voltage application with 10V amplitude. For all samples the SHG hysteresis loops were measured in the frequency range of 10 mHz – 100 kHz. Thickness dependences of switching parameters (contrast and efficiency of switching) as well as qualitative estimation of the unswitchable part of polarization are discussed. The SHG intensity dependences on the scattering angle (scattering indicatrices) were measured for NBFO thin films and planar structures. All measurements were carried out at room temperature. This work is supported partly by Russian Founadion of Basic Research and Russian Ministry of Science and Education.