Seminarium Optyczne

Molecular spectroscopy provides reference data needed for numerous applications, in particular for remotemeasurements in the Earth's atmosphere, as well as for basic research. In order to correctly model the spectra, there arenecessary full sets of line shape parameters taking into account a number of collisional effects. It turns out, however,that even such basic parameters as line positions and intensities are not known accurately enough in many cases. Mostof the available reference data do not meet the increasingly stringent requirements for applications in the study of theEarth's atmosphere, where relative per-mille accuracy for determining the concentration of various gases is needed.On the other hand, in basic research it is necessary to know the positions of the lines in the optical range even withhertz-level accuracy. Additional difficulties arise from the fact that many of the applications require the study of weakand very weak molecular transitions.Among the possible solutions to these problems there are measurements made in optical cavities, whichenable a significant extension of the effective absorption path length and elimination of some sources of uncertainty,in particular those related to power fluctuations of the probe beam and determination of the absorption path length.Spectroscopy in the cavity allows the measurement of both absorption and dispersion spectra. In the latter case, it ispossible to reference both spectrum axes to atomic frequency standards.Recent results will be presented, where for the first time it was possible to obtain per-mille level accuracy ofcarbon monoxide line intensities: the results of theoretical calculations were verified at the required level of accuracyby three different laboratories. Line positions measurements made with kilohertz and sub-kilohertz accuracy, forDoppler broadened lines and in saturation conditions, respectively, will also be presented.