Spectrum of the ion-trap laser

The spectral properties of the ion-trap laser [Europhys. Lett. 37, 317 (1997)] are investigated for a realistic multilevel scheme containing a $\Lambda$-type subsystem. In the laser region, the linewidth of the output spectrum is up to ten times smaller than the cavity damping rate and roughly proportional to the inverse of the mean photon number. Significant modifications and photon antibunching occur for thresholdless lasing. The fluorescence spectrum displays the signature of the coherently scattered resonator field.