Spectroscopy of transient molecular species for studies of exoplanet atmospheres

In one of the work packages of GACR grant application we proposed to develop experimental approach for absolute line strengths determination that is independent on the concentration of detected species: Our approach utilizes the fact, that saturation of a spectral transition, that is, the deviation from linear dependence of absorbed intensity on the incident light intensity is directly linked to the absolute line strength of given transition, and independent on the concentration of absorbing species. Thus if the absorption coefficient dependence on the laser power is quantitatively measured this important molecular property can be determined. The helping grant will be used to provide prove-of-concept measurements that will validate this novel approach. We will construct specialized low pressure absorption cell with electronic pressure regulation down to 10-2 Torr that will permit observation of saturation effects such as sub-Doppler Lamb-dips. The absorption volume will be placed in optical build-up cavity (Fabry-Perot (FP) resonator) to enhance the light intensity. Pound–Drever–Hall technique will be applied to lock the laser radiation to the FP resonator. The technique will be first tested with stable molecules, methane and acetylene, where retrieval of line strengths can be correlated with known values. If time permits the cell will be coupled with sputtering source of AlO molecule to determine it's absolute absorption cross sections in the selected spectral regions in Near IR.