This article deals with the evaluation of the chemical purity of iodine-filled absorption cells and the optical frequency references used for the frequency locking of laser standards. We summarize the recent trends and progress in absorption cell technology and we focus on methods for iodine cell purity testing. We compare two independent experimental systems based on the laser-induced fluorescence method, showing an improvement of measurement uncertainty by introducing a compensation system reducing unwanted influences. We show the advantages of this technique, which is relatively simple and does not require extensive hardware equipment. As an alternative to the traditionally used methods we propose an approach of hyperfine transitions' spectral linewidth measurement. The key characteristic of this method is demonstrated on a set of testing iodine cells. The relationship between laser-induced fluorescence and transition linewidth methods will be presented as well as a summary of the advantages and disadvantages of the proposed technique (in comparison with traditional measurement approaches).

Institute of Scientific Instruments of the Czech Academy of Sciences v v i Královopolská 147 61264 Brno Czech Republic

National Institute of Metrological Research Strada delle Cacce 91 10135 Torino Italy

Sytèmes de Référence Temps Espace SYRTE CNRS UMR 8630 LNE Observatoire de Paris UPMC 61 Avenue de l'Observatoire 75014 Paris France

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