## 1 Introduction
A diverse array of materials has been used in RIM visualization experiments. The most common solid materials employed in these experiments include: glass [4; 5; 6], plastic [7; 8; 9; 10], rubber [11; 12; 13], resin [14; 15], and hydrogel [16; 17; 18]. Liquids are classified into two categories: aqueous solutions and organic solutions. Common aqueous solutions include: sodium iodide (NaI) [19; 20; 21], ammonium thiocyanate (NH4 SCN) [22], potassium thiocyanate (KSCN) [23]. Glasses are naturally transparent and chemically stable, exhibiting excellent compatibility with a wide range of aqueous and organic fluids. Tetraethylene glycol [24], Trupentine Benzene [21], benzyl alcohol [25], p-cymene [26], mineral oil, and other organic solutions were often used to match the glasses. The selection of organic solid materials (e.g., plastic, rubber, resin) is crucial for ensuring stability and compatibility with organic liquids. Hydrogels were developed with the specific purpose of matching the refractive index of water, thereby greatly expanding the range of potential applications. RIMs with various combinations of fluid-solid systems exhibit unique strengths and weaknesses. It is of great importance to select the most appropriate materials for visualization based on the experiment's objectives (for further details regarding the various materials utilized for different applications, see Section 2). A detailed account of the various test section arrangements, fluid and solid material choices, and methods for tuning the match has been presented [27]. A broad overview of RIM in visualization techniques is provided particularly on concentrated particle suspensions [28]. [PERSON] et al. [29] provided an overview of fluid-solid and fluid-fluid systems with refractive index matches used in various fields. [PERSON] et al. [30] showed a comprehensive analysis of RIM techniques involving polymethyl methacrylate (PMMA) utilized in flow field visualization experiments. The paper compares various RIM fluid schemes for PMMA based on their refractive indices, densities, viscosities, and costs, thus providing researchers with a guide for selecting appropriate RIM fluids matched to PMMA. [PERSON] et al. [31] discussed the evolution and advancement of transparent rock soil as a solid RIM, including the experimental apparatus, optical observation techniques, and engineering applications of this technology. To the best of our knowledge, there is a lack of a comprehensive review that summarises and discusses RIM formulations for different application scenarios and experiments. In this paper, we present a review of RIM visualization experiments for specific applications in the fields of hydraulic engineering and other areas. This review could serve as a reference for researchers in the field. The paper is organized as follows. Section 2 details the application of RIM-based optical visualization technology in research in various fields. Section 3 summarises the RIM formulations in each scenario (including access to materials and experimental operations), providing a reference for researchers seeking to carry out relevant experiments. Also, the advantages and disadvantages of various RIM formulations along with potential future work are discussed in the section. Section 4 presents the summary and conclusions.