Various spectroscopic techniques have been used and most frequent are low-angle fluorescence [11], low-angle static [12] and dynamic [13] light scattering, and attenuated total reflection techniques [11],[14] and [15]. Still, these methods have limitations (i) due to sophisticated methodology; (ii) spectral interfering effects like reabsorption; or (iii) related to the limited number of detectable substances (like luminophores or Mie-scattering entities). Thus, the applications of molecular-absorption spectroscopy would be preferable. However, its common techniques are transmission-based, and their applicability to samples with linear absorptivities above 5 cm−1 is not approaching due to very strong attenuation of the probe beam. Thus, they are not suitable for samples with strongly absorbing analytes usually used in analytical chemistry (molar absorptivities or extinction coefficients above 103 L mol−1 cm−1) with their bulk concentrations above 10−3 to 10−2 mol l−1.