the lasers over the Raman resonance [@Janik1985a; @Klein1990a; @Siemers1992a; @Kurth1995a; @Barwood1998a].

The width and contrast of the ground-metastable CPT resonances depend strongly on the ground-metastable coherence dephasing rate $\gamma_{g,m}$, Eq. (\[eq:g-m\_dephasing\]). Siemers *et al*. [@Siemers1992a] used narrow-band lasers (“a few kHz”) and deduced a coherence dephasing rate of $2\pi\times 12$kHz, in agreement with the assumption of noncorrelated lasers (the actual CPT resonances were wider due to power broadening). The dephasing due to the laser linewidths was not examined in the calculations in Ref. [@Berkeland2002a]. Figure \[fig:gammaL\] shows ground-metastable CPT resonances for parameters corresponding to curve A in Fig. 7 of Ref. [@Berkeland2002a], but for different dephasing rates $\gamma_{g,m}$. As this rate approaches $\Gamma$, the CPT resonances disappear completely. The magnetic field of $150\;\mu$T is large enough to separate the four resonances as well as to destabilize metastable-level dark states (see Sec. \[sec:m-states\]). The CPT resonances have finite linewidths even for $\gamma_{g,m}=0$ due to power broadening, which is illustrated in Fig. \[fig:powerbroadening\]. Note that the blue side of the $^2S_{1/2} - ^2\,P_{1/2}$ transition cannot be scanned in a real ion trap experiment as the ion is lost due to heating.

![\[fig:gammaL\](Color online) CPT resonances for different values of $\gamma_{g,m}/\Gamma$: 0 \[solid 