can be operated either as a single photon source or as a nanolaser, depending on the pumping and pure dephasing rates. In particular, the dramatic influence of pure dephasing on the lasing threshold could be evidenced on such a device. We have studied the dynamics of a two-level atom undergoing pure dephasing, coupled to a single cavity mode, and derived an effective atom-cavity coupling rate, which has been shown to be a useful and conceptually simple parameter to be used in the description of the physics of the problem. In particular, it allowed us to generalize the notions of good and bad cavity regimes. In the bad cavity regime, we have defined a generalized Purcell factor, and studied the strategies to optimize broad emitter-based single photon sources. We have shown that if the atom and the cavity are detuned, increasing pure dephasing can improve the figures of merit of the device. In the same way, we have shown that in the good cavity regime, lasing can even be induced by increasing pure dephasing. These results enforce the idea that pure dephasing is a promising resource, specific to solid-state emitters, which might be used to develop advanced nano-photonic devices like single photon sources and nanolasers, and could allow to improve their performances. These ideas could be directly checked on an innovative and versatile device based on the control by pure dephasing of the coupling between a single QD and a semi-conducting cavity. This work was supported by NanoSci-ERA consortium and by the EU under ERANET project LECSIN, by the Nanosciences Foundation of Grenoble, the CNPq, the Fapemig, and the ANR project CAFE. DG acknowledges stimulating discussions with A. Imamoˇ glu and T. Volz. [1] E. M. Purcell, Phys. Rev. 69 , 681 (1946). [2] P. Goy, J. M. Raimond, M. Gross, and S. Haroche, Phys. Rev. Lett. 50 , 1903 (1983). [3] R. J. Thompson, G. Rempe, and H. J. Kimble, Phys. Rev. Lett. 68 , 1132 (1992). 19 Acknowledgments VI. CONCLUSION