Lasing without inversion in three-level systems without external coherent driving

Abstract

We have studied an incoherently pumped laser operating with a Doppler-broadened three-level system placed in a doubly resonant cavity. This system generates two laser fields, one of them without population inversion. Both ladder and V-type three-level schemes are considered with a ratio $R={\ensuremath{\omega}}_{\ensuremath{\alpha}}/{\ensuremath{\omega}}_{\ensuremath{\beta}}$ of inversionless laser frequency ${\ensuremath{\omega}}_{\ensuremath{\alpha}}$ to ordinary laser frequency ${\ensuremath{\omega}}_{\ensuremath{\beta}}$ of $R=0.67$ and $R=1.88,$ respectively. Dual-wavelength lasing extends up to Doppler-broadening values for optical transitions of atoms in a vapor cell. Some considerations for the practical realization of this dual-wavelength laser are discussed.