Efficient technique for measuring laser frequency stability

We propose a new technique for measuring the frequency stability of cw laser radiation. The technique relies on using the laser to be tested as a coupling laser in a scheme of electromagnetically-induced transparency (EIT), either on a $\Lambda $ or a ladder system. A second, frequency tunable laser (stabilization of this laser is not needed) is used both to act as the EIT probe laser, and to form an atomic frequency reference spectrum. The frequency stability is monitored via the frequency deviation of the EIT resonance with respect to an atomic reference frequency. We also present an improved dichroic atomic vapor laser lock (DAVLL) method for frequency stabilization based on a nanocell with a $\lambda /2$ thickness.