ABSTRACT
Different modalities of optical absorption spectroscopy in a spectral range from the ultraviolet (UV) to the infrared (IR) spectral region are among the most common analytical tools in chemical analysis. Absorption measurements can be realized in laboratory instrumentation such as ultraviolet–visible (UV/Vis), near infrared (NIR), or Fourier-transform infrared (FT/IR) spectrometers, but it is als o performed outside the chemist’s lab, for instance, in atmospheric science by LIDAR (light detection and ranging) or DOAS (differential optical absorption spectroscopy), or in industrial process analysis by specially tailored sampling probes. However, all these absorption spectroscopy techniques entail several well-known drawbacks and limitations. The optical absorption is not measured directly, but rather derived from the ratio of injected to transmitted light intensity at a given wavelength. Hence, discrimination between optical absorption and light scattering is not possible. Furthermore, the measured signal is inversely proportional to the concentration of the absorbing species in the light path, thus resulting in high signals for low concentrations and vice versa. The metrology for such tasks is demanding due to the higher noise at absolutely higher signals and limits the dynamic concentration range of classical absorption spectroscopy.
