Compressed fluid systems handled in high pressure processes feature diffusivities smaller than the kinematic viscosity. Therefore during mixing the lifetime of micro(µ)-scale(s) inhomogeneities exceeds that one of macro(m)-scale(s) inhomogeneities. Thus m-s homogeneous systems can still exhibit µ-s inhomogeneities. They affect the functioning-chain of processes, e.g. reactions and phase-transitions or –separations, which themselves also take place on a sub-macro-scale.Therefore it will be analyzed in situ how µ-s inhomogeneities influence the functioning chain of the particle generation (supercritical antisolvent technology), the reaction (high pressure combustion), and the phase-separation or phase-transition mechanisms (surfactant-free CO2-based micro-emulsions and gas hydrates) and to which extend these inhomogeneities are responsible for the characteristics of the product, such as unfavourable size distributions of particulate products and/or pollutant emissions.On this purpose the here proposed and self-developed non-invasive and in situ Raman spectroscopic technique considers the INTENSITY-ratios of Raman signals to analyze the m-s composition and the SIGNATURE of the OH stretch vibration Raman signal of water (or alcohols) to analyze the µ-s composition of fluid mixtures. The SIGNATURE of the OH stretch vibration Raman signal is influenced by the development of the hydrogen bonds -an intermolecular interaction- and thus provides the µ-s composition, though the probe volume of the Raman sensor is m-s. The signal-INTENSITY-ratio and signal-SIGNATURE are extracted both from one and the same “m-s” Raman spectrum of the mixture. This allows the comparison of the degree of mixing on m-s and µ-s simultaneously, and enables the analysis of whether a system at any instance of mixing (instance of the onset of a reaction or a phase transition or –separation) has reached the favourable µ-s homogeneity, which would result in homogeneous and uniform products.