# Editorial Board Members' Collection Series: Nonlinear Photonics
## 2 An Overview of the Articles in This Special Issue
This nonlinear optical method allows one to distinguish various types of nontrivial magnetic states, such as magnetic vortices, magnetic toroidal moment, and gradients of magnetization [9]. Reference [9] is a comparative study of linear and nonlinear magneto-optical effects in IrMn/CoFe films of various thickness of the ferromagnetic CoFe layer. It demonstrates that the magneto-optical response of the pinned AFM/FM nanofilms appears with different hysteresis loop parameters in the transverse magneto-optical Kerr effect (MOKE) and interface-sensitive magnetization-induced second harmonic generation (SHG), indicating the diversity of the magnetic effects at interfaces compared to the bulk of the films. In reference [10], localized surface plasmon (LSP) modes in a design comprising two coupled nano-ridges deposited on a gold layer with an interposing polymer spacer layer are numerically investigated. Such a structure is usually referred to as a particle-on-mirror structure. First, the LSP modes of a single nano-ridge and the analysis of its scattering cross-section in the visible and infrared ranges are examined. To enhance the plasmonic response, a thin polymer layer is placed at the middle of the ridge, which introduces additional LSP modes confined within the former. Then, the analysis is extended to the dimer configuration, which yields LSP resonances with a quality factor enhancement of approximately threefold relative to a single nano-ridge. Furthermore, the presence of the polymer layer within the ridges significantly improves plasmon field localization and the quality factor. These findings underscore the potential of nano-ridge-based structures in advancing optomechanical coupling and offering valuable insights for the development of high-performance acousto-plasmonic devices. In particular, the proposed device could help significantly improve the design of nano-acousto-optic modulators, operating in the visible or in the near-infrared ranges, that require an enhanced light-phonon coupling rate. The field of photovoltaics (PV) continually seeks innovative material solutions to enhance the efficiency and the stability of their standard devices. In reference [11], the use of plasmonic core-shell nanoparticles in PV applications through various experimental validations is reviewed. Advancements in the design and in the control over the properties of core-shell nanoparticles are described and their integration into various solar cells, based on their ability to finely tune optical, electronic, and chemical properties, are highlighted. Experimental results for organic, perovskite, and dye-sensitized solar cells are discussed, where core-shell nanoparticles have been successfully deployed. Additionally, gaps in the current research are identified, such as the need for scalable synthesis methods and long-term stability assessments and promising new developments at the frontier of the field. Today, fluorescence microscopy is used worldwide, despite suffering from drawbacks such as photobleaching, phototoxicity, and challenging quantification. Most small biomolecules, such as nucleosides, amino acids, fatty acids, choline, glucose, and cholesterol, are intrinsically nonfluorescent, so fluorescent tags are mandatory. Unfortunately, these tags, such as organic dyes, fluorescent proteins, or quantum dots, are all relatively larger than small biomolecules; consequently, they can severely falsify their native biochemical or biophysical properties. Therefore, label-free imaging, with high sensitivity and high chemical selectivity of unlabeled living cells, is preferable. In this framework, vibrational microscopy techniques have emerged as a powerful approach based on a chemically label-free selective contrast due to intrinsic molecule vibrations. Among them, stimulated Raman scattering (SRS) microscopy, which was adapted to microscopy only in the last two decades, is one of the most promising techniques.