Odor markers present in natural gas are useful tracers for imaging of the gas/air mixing progress in tech. burner applications. Since tetrahydrothiophene (THT) is commonly used to odor mark natural gas, it is a 'natural' compd. present in a wide range of tech. combustion systems. The spectroscopic properties of this compd. are investigated in static cell expts. giving the background for quant. interpretation of laser-induced fluorescence (LIF) of THT in isothermal systems. The technique is used to characterize the mixing process of the isothermal and the combusting flow in a tech. scale turbulent burner.