Nonlinear Optical Microscopy of Interface Layers of Epitaxial Garnet Films

Abstract

The structure of magnetic domains is an exciting research object that shows an enormous variety of delightful patterns. Epitaxial garnet is one of the most studied magnetic dielectrics with well-recognized bulk domains, while the magnetic composition at the surface is less investigated. Here we apply the nonlinear optical microscopy technique for the visualization of the interface magnetic domains of 10 μm thick (LuBi)3Fe5O12 film and prove that it is qualitatively similar for both garnet/air and garnet/substrate interfaces. As an efficient extension of the second harmonic generation microscopy, we suggest and demonstrate the possibilities of the third harmonic generation one, which provides higher resolution of the method.

Third harmonic generation microscopy of magnetic domains in garnet films

“…In order to fix the scanning area in the SHG and THG microscopy studies, we burned the garnet film by an intense focused laser beam within a local spot of about 2 µm in diameter and used it in further measurements as the reference point; it appears as a dark area in the SHG pattern. Similarly to the results demonstrated recently [20], magnetic domains in figure 4(a) are seen as stripes with strongly different SHG power, which shows that magnetic SHG terms of the nonlinear polarization are comparable to the crystallographic ones. For the perpendicular polarizations of the pump and SHG waves, a chess-like (or zig-zag) SHG pattern appears, which is associated with the interface blocking domains with inclined average magnetization.…”

“…As stems from the analysis of the THG and SHG microscopy patterns obtained for different combinations of polarizations of the pump and harmonics' waves, the inplane average orientation of magnetization in these interface domains differs from that of the bulk stripe ones. The average magnetization in adjacent surface domains forms an angle smaller than π, which also correlates with our previous magnetic force microscopy (MFM) results [19,20].…”

“…The THG intensity patterns measured for the perpendicular polarizations of the fundamental and THG beams reveal the presence of magnetic stripe domains, which indicates the presence of both even and odd in M components of the THG polarization in that case. This means that the magnetization of the stripe domains is inclined with respect to the domain axis in appliance with our previous studies of similar garnet films by means of the SHG microscopy [19,20]. The presence of the symmetry forbidden crystallographic THG components in that case can be due to a small misalignment of the polarization plane of the pump beam, a possible reason for this can be the linear Faraday rotation of the fundamental beam.…”

“…Speaking about the nonlinear optical microscopy, it was SHG that was first applied for the visualization and studies of magnetically ordered crystals [16][17][18]. Recently, the organization of magnetic domains at the surface and buried interface of epitaxial garnet films was studied by the SHG microscopy [19,20]. Concerning the THG microscopy of magnetic structures, the research progress is more modest; it was shown that magneto-optical effects at the THG wavelength are comparable to linear optical ones in nanostructured ferromagnetic metals [7], garnet-based films [21,22] and magnetophotonic microcavities [23].…”

Special Issue on New Trends in Nonlinear Optics in Nanostructures and Plasmonics

“…The generation of laser radiation harmonics can be utilized to develop unique tools for studying the surfaces of materials. In [3], magnetization-induced second and third harmonic generation of a femtosecond laser radiation of an optical parametric oscillator at 740-1800 nm has been applied for the visualization of the interface magnetic domains of 10 µm thick (LuBi) 3 Fe 5 O 12 garnet film. It has been shown that the technique of nonlinear optical microscopy based on third harmonic generation provides better spatial resolution compared to microscopy based on second harmonic generation.…”