Samenvatting

This project helps to reach the end goal of doing long distance measurements. Long distance measurements depends on the refractive index of air. The refractive index depends on temperature, pressure, humidity and gas mixture. The biggest uncertainty of calculating the refractive index is the temperature, as ambient fluctuations are non-uniform across space. Measuring the temperature optically using spectroscopy is a method that can be used to accurate detect temperature fluctuations, when looking at the absorption profile of in this specific case two gases, oxygen and carbon dioxide. Two gases were selected to be able to compare the measurements with each other when performed in air. The absorption spectra of O2 and CO2 were detected with two different spectrometers. The two different spectrometers operate in different wavelength ranges. Both the setups use the same frequency comb laser as an illumination source.

The spectrometer to detect O2 lines was built as a part of this project and a first O2 spectral measurement was demonstrated. The CO2 spectrometer was also realigned and a CO2 measurement was performed. Both the beams were also made to co-propagate through the same gas cell so that simultaneous measurements could be performed on the same gas volume using the two spectrometers.

To obtain an absorption spectrum two measurements are done. First a measurement is done with a reference gas, during this project nitrogen is used. The gas cavity is then evacuated with a vacuum pump and then filled with a gas(mixture) of choice. Using a MATLAB program the ratio between the reference and measurement is converted to an absorption spectrum. This thesis presents measurements of the absorption spectra of O2 and CO2. The measured absorption spectra are then compared with spectra from the HITRAN database. At the end of the project the absorption spectra only need be optimised to perform temperature measurements.