Prediction of inversionless gain in a mismatched Doppler-broadened medium

Inversionless gain is predicted in a Doppler-broadened [Formula Presented] scheme for which the probe laser frequency is approximately twice that of the coupling laser. A comparison is made of inversionless gain achieved via electromagnetically induced transparency in Doppler-broadened matched and mismatched wavelength systems. We show that the presence of Doppler broadening does not preclude inversionless lasing for mismatched wavelengths; importantly, this is shown to hold even for Rabi splittings significantly less than the Doppler width. Our analysis demonstrates that inversionless gain is realizable in Doppler-broadened media, at modest continuous wave laser powers, for a probe frequency well in excess of the coupling field frequency. The presented theory is related to a practical mismatched system in atomic rubidium vapor. Approximately 8% gain is predicted in a 422 nm probe field coherently driven by a 780 nm coupling field, in the presence of a modest level of incoherent excitation.