Purity of iodine cells and optical frequency shift of iodine-stabilized He-Ne lasers

In this paper we present an investigation of a set of short iodine cells designed to operate in the intracavity arrangement in iodine-stabilized Helium-Neon laser etalons. The cells were made over a longer period of time, their absolute optical frequencies were measured in international comparisons and their frequency shifts are compared here to independent measurement of iodine purity performed by measurement of induced fluorescence and evaluation by the Stern-Volmer formula. The manufacturing technology of the cells and the filling process is mentioned briefly and the arrangement for measurement of the induced fluorescence is described. The main goal of this effort is to recognize the limits of the absolute precision of the optical frequency of iodine transitions and look for further improvements in the iodine cell manufacturing technology that may lead to even smaller frequency shifts.