Laser Polarization Noise & CPT Atomic Clock Signals

In the typical CPT clock, circularly polarized light creates a superposition state between the two m_F = 0 ground state sublevels via a common m_F = +1 (or m_F = -1) excited state. If the laser polarization suddenly changes, the common excited state will change (e.g., m_F = +1 rarr m_F = -1). This introduces a transient into the CPT signal, which can degrade the clock\´s signal-to-noise ratio. Here, we present preliminary results from our experiments examining this issue. In particular, we find that a change in laser polarization leads to a transient change in the CPT signal via two processes. The first appears to be associated with the re-establishment of an equilibrium electronic spin polarization in the vapor, langS_zrang, which in a four-level model of the CPT signal can be thought of as a re-establishment of the "trapping state" population; the second process is still under investigation. Each of these processes has a unique timescale, and both will be important for understanding a CPT signal\´s response to laser polarization noise.