Merits and Limitations of Submillimeter Wavelength Frequency Standards Based on an Mg(Ca) Metastable Beam

Magnetic field independent transitions in Mg(Ca) metastable levels were recognized as metrologically interesting for the realization of high-performance frequency standards in the submillimeter wavelength region. This paper presents an analysis of their merits, theoretical limitations, and technological difficulties. Projections are made for the performances of standards based on these transitions.