## 1 Introduction  
Emulsions are widely used in food, pharmaceutical, and chemical industry [1]. Compared to homogeneous systems, emulsions are more complex regarding their structure and resulting properties [2]. Their higher complexity arises from various parameters, such as the size distribution of the inner droplet phase and the interfacial properties, as well as the compositions of each phase [3]. The requirements for the measurement techniques used are therefore high. The interfaces between the phases can be especially challenging [4, 5]. To monitor chemical reactions, optical measurement technologies are a widely used tool [6]. Raman spectroscopy has started to play a more important role during recent years [7]. In industry, Raman spectroscopy is used to monitor emulsion polymerization processes [8], to ensure food quality [9, 10] and for the development of new pharmaceuticals [11]. One major advantage of Raman spectroscopy is its high selectivity for molecular bonds [12]. Furthermore, the intensity of the Raman signal correlates with the concentration of the sample [12]. Both characteristics suggest that Raman spectroscopy is ideally suited for measuring heterogeneous systems such as emulsions. However, a special problem arises when measuring emulsions [13]. The interface between the continuous phase and the dispersed phase leads to elastic scattering of the incident light [14]. This is because the refractive indices of the disperse and continuous phases differ. This results in refraction and reflection at the interfaces [15]. Due to these effects, the light does not enter the emulsion droplets unhindered, but is scattered away from the primary direction. Depending on the measuring device, this effect leads to strong disturbances in the measurement process and makes interpretation of the results more difficult. The strength of the reflections can be quantified using the reflectance \(R\)[15]. To calculate the reflectance, two cases, the reflectance of perpendicular polarized light \(R_{per}\) and parallel polarized light \(R_{pur}\), need to be considered. The equations for both parameters can be derived from the [PERSON]'s formula. In the following, the case of the same magnetic permeability of the emulsion phases, which is generally valid for emulsions, is shown  
\[R_{per}=\frac{sin^{2}(\alpha-\beta)}{sin^{2}(\alpha+\beta)}, \tag{1}\]  
\[R_{par}=\frac{tan^{2}(\alpha-\beta)}{tan^{2}(\alpha+\beta)}. \tag{2}\]  
To determine the reflectance for non-polarized light, the mean value [15] of the perpendicular and parallel polarization needs to be calculated. \[R=\frac{R_{per}+R_{par}}{2} \tag{3}\]  
For the special case of perpendicular polarized light, \(\alpha=\beta=0^{\circ}\), which results in cosine functions of \(1\) and simplifies the formula [15] as follows:  
\[R=\bigg{(}\frac{N_{1}-N_{2}}{N_{1}+N_{2}}\bigg{)}^{2}. \tag{4}\]  
Due to the high disperse phase fractions of more than 70% commonly found in emulsions [16], multiple scattering occurs caused by the numerous phase interfaces [13]. An important role is played by the refractive index difference: the phase ratio and the droplet size distribution; and also by the geometry of the incident light, its focusing at the focal point and other imaging conditions. This challenge is increased further when the microstructure of double emulsions has to be evaluated. Double emulsions are emulsions within emulsions, i.e., complex multiphase systems in which both water-in-oil (W/O) and oil-in-water (O/W) emulsions exist simultaneously [17]. The most common case is a water-in-oil-in-water (W/O/W) emulsion, where one to numerable water (W\({}_{1}\)) droplets are dispersed within oil (O) droplets, which form an emulsion themselves by being dispersed within the second water (W\({}_{2}\)) phase [18]. One key advantage of the double emulsion structure is the ability to encapsulate active or sensitive substances [19], as e.g., enzymes, vitamins or crop protection agents. The middle phase can be solidified and used as a protective shell [20].