This work shows the interest to use a real time white laser-based ellipsometer to characterize complex electrolyte | electrode interface during electrochemical process in aqueous-based medium. This method is proposed to probe electrochemical interfaces which are usually not suitable to the full extent application of ellipsometry due to great disturbance of the reflected light flux provoked by gas evolution or roughness. In situ spectroelectrochemical ellipsometry combining such a visible super continuum fiber laser-band source was not previously reported to the best of the authors' knowledge. The setup was employed to monitor an electrochemical process whose the mechanism was previously incompletely described: the pre-spark anodization regime of plasma electrolytic oxidation process of Mg alloy AZ91D in 3 M KOH electrolyte. Above the anodization voltage of 4 V, the side water oxidation reaction induced light diffusion that reduces reflected light beam intensity. The process is here monitored in an extended This is the author's peer reviewed, accepted manuscript. However, the online version of record will be different from this version once it has been copyedited and typeset. PLEASE CITE THIS ARTICLE AS 2 voltage range from 4 to 40 V and in an extended spectral range (495-800 nm). In the presented case, the use of a visible super continuum fiber laser-band source enhanced the signal-to-noise ratio giving access to a more deeper picture of the triplex layer structure during surface repassivation by monitoring the evolution of the outer, inner and interfacial layers.