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Conference on Lasers and Electro-Optics

A study of inversionless gain in mismatched, Doppler-broadened systems

J. R. Boon, E. Zekon, David McGloin, Malcolm H. Dunn

Published Nov 27, 2002• 0 citations
Publisher

Abstract

Summary form only given. We present the results of a comparative study of a matched and a mismatched system, in which all parameters are made equal except the transition wavelengths. Density matrix analysis demonstrated that the gain produced for a given incoherent pumping rate is spread out in frequency for the widely split mismatched system, and that while the peak gain is less, the total net gain is in fact greater than that predicted.

DOI
10.1109/iqec.1998.680302

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Chinese Physics•Oct 1, 2007•1 citation
Summary form only given. We present the results of a comparative study of a matched and a mismatched system, in which all parameters are made equal except the transition wavelengths. Density matrix analysis demonstrated that the gain produced for a given incoherent pumping rate is spread out in frequency for the widely split mismatched system, and that while the peak gain is less, the total net gain is in fact greater than that predicted.
Inversionless gain is predicted in a Doppler-broadened VVV 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.
Continuous inversionless gain is studied in a Doppler-broadened Λ scheme. The inversionless gain is realizable in Doppler-broadened media for a coupling field wavelength well in excess of probe field wavelength when the laser power is significantly less than the Doppler width, and stronger than that of media for the coupling field wavelength equal to the probe field wavelength. In another scheme for the probe field wavelength well in excess of coupling field wavelength, the inversionless gain doesn't exist. The predictions are explained form the point of electromagneticaly-induced transparency.
A study is made of the effects of Doppler broadening on pure gain without inversion, which means that neither one-photon nor two-photon inversions are allowed, and non-pure gain without inversion, which means that one-photon inversion does not occur but two-photon inversion is present, in a closed Λ-type three-level system with incoherent pumping. It is shown that when the driving field is resonant but the probe field is not, in a certain range of Doppler width, for the case of the lower degree of frequency up-conversion, generally, pure gain without inversion increases monotonically and non-pure gain without inversion does not monotonically increase or decrease with increasing Doppler width; for the case of the higher degree of frequency up-conversion, pure gain without inversion decreases monotonically but non-pure gain without inversion cannot be produced. In the case of two-photon resonance, in some range of Doppler width, pure gain without inversion does not monotonically increase or decrease while non-pure gain without inversion decreases monotonically with Doppler width increasing. Finally, an experimental scheme for examining our theoretical result is given.
An analysis is made of the effect of Doppler broadening on gain without inversion (GWI) from different aspects in a closed lambda-type three-level system with an incoherent pump. It is shown that, regardless of the driving field being on resonance or not, for the counter- or co-propagating of the probe and driving fields (PDF), GWI does not monotonically decrease or increase with increasing Doppler width. Except for the case of counter-propagating PDF with off-resonance driving field, at a suitable Doppler width one can obtain a gain maximum value much larger than that without Doppler broadening; especially in the situation of the resonant driving field, the co-propagating geometry leads to a larger GWI. In addition, for the counter-propagating geometry, when Doppler width is larger enough, GWI oscillation occurs, and the oscillation amplitude and region increase with increasing Doppler width. These conclusions are very different from that obtained in previous investigation (Lukin et al, Laser Phys. 6 436 (1996)).