Todays energy supply relies on the combustion of fossil fuels. This results in emissions of toxic pollutants and green-house gases that most likely influence the global climate. Hence, there is a large need for developing efficient combustion processes with low emissions. In order to achieve this, quantitative measurement techniques are required that allow accurate probing of important quantities in combustion devices. Temperature is very important in combustion processes, especially for chemical reaction rates and, hence, for pollutant formation. The versatile measurement techniques developed and improved within this thesis enable quantitative probing of the gas temperature in practical combustion devices. Accurate knowledge of this important quantity allows developing efficient power plants and engines with low emissions of green-house gases and toxic pollutants.