Nonlinear optical scanning microscopy based on the generation of the second harmonic generation (SHG) allows to explore the domain structure of ferroelectrics and multiferroics, effects of polarization switching and phase transitions. This paper discusses the possibilities and limitations of these technique for the study of thin films and multilayer structures with ferroelectric and multiferroic properties.
Local polarization switching is studied in thin films and nanostructures based on BaSrTiO3, the reasons for spatial inhomogeneity of switching are analyzed. In ferroelectric/ferromagnet (multiferroic) bilayer and multilayer planar nanostructures ferroelectric and magnetic phase transitions are studied, as well as influence on non-linear optical properties of the effect of electron tunneling through a ferroelectric. In centrosymmetric/centrosymmetric superlattice breaking of centrosymmetry and appearance of polar structure was observed and confirmed by SHG microscopy.
Femtosecond lasers are widely used for material treatment such as laser cutting (including laser surgery) and drilling, micro- and nano-structuring. Main advantages of femtosecond laser use are based on details of laser-matter interaction which provides the lower energy impact accompained by high pulse power density, the reduction of thermal damage, the elimination of laser-plume interaction. Here we report about developing a method of femtosecond laser annealing of precursor ferroelectric film to perovskite microstructures accompained by in-situ SHG monitoring of annealing process and ex-situ SHG microscopy of annealed areas.
Recently new techniques breaking the diffraction limit in far-field imaging were developed based on a spatial shaping of the laser beam from Gaussian to doughnut. For luminescence objects such as semiconductor nanoparticles the stimulated emission depletion microscopy (STED) is used providing spatial resolution of about 50 nm [1]. Alternatively for nonfluorescent species microscopy based on saturation of electronic absorption is applied [2]. Here we discuss the possibilities and limits for applications of these techniques for ferroics, including for the studies of ultrafast processes.
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2. Pu Wang, Mikhail N. Slipchenko, James Mitchell, Chen Yang, Eric O. Potma, Xianfan Xu J.-X. Cheng, Nature Photonics 7, 449 (2013).