A constant potential at the respective, previously measured OCP was applied to the working electrode using the CHI760E bipotentiostat. A rectangular-shaped modulated potential, produced by a Waveform generator (PSG9080, Joy-IT), with a modulation frequency of 67 Hz and a variable amplitude as an offset was superimposed. Meanwhile, the working electrode was transilluminated by monochromatic light generated by a QTH lamp (Apex2, Oriel Instruments) of wavelengths selected by a monochromator (Cornerstone 130, Oriel Instruments). At certain wavelengths long-pass filters (570 nm and 1000 nm) were introduced into the beam path to block components with a higher diffraction order. The transmitted light was detected by an InGaAs detector (Thorlabs, DET05D), and the signal was passed to a lock-in amplifier (MFLI, Zurich Instruments). In parallel, the lock-in amplifier received the modulated potential generated by the signal generator as a reference signal and searched for a modulated component in the optical signal that oscillated at the same frequency. In the Supporting Information a detailed schematic illustration of the EMAS setup is included (see Figure ). Considering the phase relationship between the modulated potential and the modulated component in the optical signal, it was determined whether the measured signal was an induced absorption or a bleach (for more information, see the discussion section). During the EMAS measurement, the modulated potential component was applied to the sample in such a way that the total potential always oscillated between the respective OCP and a corresponding reductive or oxidative potential. At the beginning of the measurement, the peak-to peak amplitude was 60 mV. With an appropriate offset, the signal was then shifted to positive or negative values, so that the potential was modulated between OCP and OCP ±60 mV. At this potential, a complete spectrum from 850 to 2100 nm was scanned in 5 nm steps. Afterward, the peak-to-peak amplitude was increased by 60 mV, the signal offset was adjusted accordingly, and a complete spectrum was recorded again. This was repeated until the final corresponding oxidative or reductive potential was reached. During the EMAS measurement, iR-compensation by the integrated positive feedback function of the CHI760E was activated and a compensation level of 92% was chosen. The measurement sensitivity of the bipotentiostat was set to 0.1 mA/V and the ACcoupled signal input of the lock-in amplifier was set to 10 MΩ with an input range of 10 mV. Incoming signals were processed by a 6 thorder low-pass filter having a time constant of 100 ms. The resolution of the monochromator was set to 5-7 nm by setting the input and output slit width to 400 µm. The potential of the measured data was also converted to the formal potential of the external redox couple Ferrocene/Ferrocenium (Fc/Fc + ), which was measured at 357 mV versus Ag pseudoreference electrode for IHO substrates in 0.