# Editorial Board Members' Collection Series: Nonlinear Photonics
## 2 An Overview of the Articles in This Special Issue
These simulation results provide a beneficial reference value for the extra-cavity shaping of different solitons that come from nonlinear optical systems. Optimally, the reported results could pave the groundwork for industrial growth in ultrafast laser design. It is well known that graphene has an extremely strong third-order nonlinearity compared to the commonly used dielectrics and metals; this nonlinearity results from the interaction of the charge carriers in graphene with strong electromagnetic radiation. Reference [7] focuses on the problem of a monochromatic terahertz TE-polarized wave propagation in a plane dielectric layer filled with a homogeneous isotropic medium; one of the boundaries of the waveguide is covered with a layer of graphene. On the one hand, in the study, energy losses both in the dielectric layer and in the graphene layer are neglected; the latter assumption is reasonable in the terahertz range of electromagnetic radiation (on which the paper focuses), where graphene has a strong plasmonic response and much less loss. On the other hand, this study considers the significant third-order nonlinearity resulting from the interaction of the electromagnetic wave with the charge carriers in the graphene layer. Besides studying the problem analytically, the paper presents some numerical results as well. In particular, the obtained results demonstrate how the nonlinearity in graphene affects the propagation constants and eigenwaves, providing the dispersion curves and eigenwaves for nonlinear graphene as well as for the linear one. LiNbO\({}_{3}\):Mg (5.0 mol % or 0.85 wt %) is a LiNbO\({}_{3}\) single-crystal-based, optically highly perfect and compositionally uniform material. It has a low photorefraction effect and it is currently used for optical frequency conversion in the phase quasi-phase-matchingmode on regular domain structures (PPLN--periodically-poled LiNbO\({}_{3}\)). However, the strong single doping decreases the compositional and optical uniformity of a single-doped crystal compared with a nominally pure congruent crystal. Doping (including double and multiple doping) provides finer control than single doping, controls many properties of an LN crystal, and also influences the type and concentration of defects in a crystal, which significantly affects the magnitude of the photorefraction effect and the optical damage resistance of the crystal. In reference [8], the features of the defect structure, compositional uniformity, and photorefractive properties in a double-doped LiNbO\({}_{3}\):Gd:Mg (Gd concentration of 0.003, Mg--0.65 wt % in the crystal) single crystal are investigated using several optical methods: laser conoscopy, photoinduced light scattering (PILS), optical spectroscopy, and Raman scattering. The crystal has been shown to have no photorefraction effect and high optical uniformity. Nonlinear optical coefficients are higher in perfect double-doped LiNbO\({}_{3}\) crystals, including those co-doped with magnesium, compared with single-doped crystals. A promising method for the optical control of the pinning effect in antiferromagnetic (AFM) and ferromagnetic (FM) interface is laser-induced heating; namely, as the structure is heated above the blocking temperature, the pinning is destroyed. A complete reversal of the exchange bias at the AFM/FM interface can also be induced by a single femtosecond pulse of sufficiently high energy. Spin precession in magnetic structures subjected by ultrashort excitation provides extensive information on magnetic interactions. Laser pulse perturbation is found to modify the exchange bias, as evidenced by the shift of the hysteresis loop with respect to the applied DC magnetic field as observed by the magneto-optical Kerr effect [9]. In optical second harmonic generation (SHG), when applied in studies of magnetic structures, magneto-optical effects at the SHG wavelength appear with typical values of one to two orders of magnitude higher than their linear analogs such as the magneto-optical Kerr effect (MOKE).