Reactive Fluids: Laser Diagnostics

The Laser Diagnostics group headed by Prof. Thomas Dreier and Dr. Torsten Endres is devoted to the development and practical application of optical measurement technique for use in combustion systems or other reactive flows. This includes laser-based methods such as Rayleigh scattering, spontaneous Raman scattering, laser-induced fluorescence (LIF), laser-induced incandescence (LII), and diode-laser absorption spectroscopy.

The team carries out fundamental experiments that enable the quantitative interpretation of measurements even in complex situations. This includes the determination of fluorescence lifetimes of small molecules (OH radical, formaldehyde, toluene, naphthalene) to clarify intra- and intermolecular energy transfer processes that are responsible for variations in signal intensity and spectra. Another example is the identification of light absorption in thin films of aqueous solutions in the near-infrared spectral range. In addition, the group also contributes to the development of laser-optical techniques (such as LII) used to measure the size of gas-borne nanoparticles  – e.g. for measuring soot in engines or nanoparticles in synthesis reactors.

The measurement techniques are employed for identifying important parameters in flames or other environments that are of interest from a practical point of view. One focus is on imaging techniques for two-dimensional visualization of mixing, reaction, and flow. The thickness and temperature of aqueous liquid films is measured using tunable NIR diode lasers via absorption spectroscopy for the time-resolved analysis of quickly evaporating liquid films on hot surfaces. Contact-free quantitative measurement of heat release in turbulent flames are carried out with LIF imaging of OH and formaldehyde as well as time- and spectrally-resolved detection of chemiluminescence (OH*, CH*, CO2*).