Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

Physical Review A

dc-field-coupled autoionizing states for laser action without population inversion

G. S. Agarwal, Seenipandian Ravi, J. Cooper

Published May 1, 1990• 97 citations
Publisher

Abstract

We consider how externally coupled (e.g., dc-field-coupled) autoionizing states can be useful in producing gain without population inversion. The dc fields produce new absorption minima that enable one to obtain laser action in different frequency regions depending on the strength of the coupling. We calculate absorption and emission profiles assuming that one of the autoionizing states is incoherently pumped as in most conventional laser models. We present numerical results that demonstrate gain regions without population inversion.

DOI
10.1103/physreva.41.4721

Related papers

Lasers without inversion: Raman transitions using autoionizing resonances

G. S. Agarwal, Seenipandian Ravi, J. Cooper

We consider laser action on a transition involving an autoionizing state \ensuremath{\Vert}a〉 and an initially unpopulated state \ensuremath{\Vert}f〉, the population of which builds up because of spontaneous emission and Raman processes. The autoionizing state is pumped by a coherent field. We discuss the transient amplification of the probe field on the lasing transition for a range of parameters. The coherent field on the pumping transition leads to minima in the absorption spectra if the atomic population were in the state \ensuremath{\Vert}f〉. Such regions of minima can be used for obtaining gain even for long times.

Physical Review A•May 1, 1990•75 citations

A simple model of laser without inversion

P. Ru, L. M. Narducci, Marlan O. Scully +1 more

The emergence of laser action from an atomic system without population inversion is beginning to attract theoretical and experimental attention as a possible way of generating useful coherent radiation at unusual wavelengths. The goal of this communication is to clarify the physical origin of this phenomenon using a four-level system whose ground state consists of two quasidegenerate levels that are coupled to a higher-lying state by a Raman-like transition. In the presence of the ground-state coherence induced by the Raman field, we calculate the absorption spectrum of a weak probe whose tunable frequency scans across the transition frequencies between the two ground-state levels and another higher-lying state that may or may not be weakly excited by an incoherent pump mechanism. Our calculation, based on a dressed atomic state approach, clarifies the conditions that must be satisfied to produce gain, identifies the frequency (or frequencies) at which the gain is maximum, and elucidates the functions of the incoherent pump, the Raman field, and the coherence between the ground-state levels in this process. An appropriate set of Maxwell- Bloch equations for a ring-cavity model of this system confirms the appearance of laser action when the small-signal gain conditions are satisfied.

Annual Meeting Optical Society of America•Jan 1, 1990•0 citations

Physical origin of the gain in a model of a laser without inversion

Heide Doss, Lorenzo M. Narducci, Marlan O. Scully +2 more

We consider a four-level atomic system with a degenerate or quasidegenerate ground-state doublet and two excited states. One of the upper levels is coupled to the ground doublet by a coherent field of variable strength, which we refer to as the Raman field, whose role is to create atomic coherence between the driven atomic states. The other higher lying state is coupled to the ground states when laser action develops. This model includes an incoherent pump mechanism to create some population in the top lasing state. In appropriate conditions, for the incoherent pump rate and the Raman field strength, the absorption profile of the laser transition develops gain features. We discuss the physical origin of this gain which we find to be the consequence of a population inversion between dressed atomic states. It is interesting to compare the results of this analysis with a similar study of a three-level lambda system which was previously recognized to yield lasing without inversion.1 In this case the appearance of gain can be attributed to the induced atomic coherence.

Annual Meeting Optical Society of America•Jan 1, 1991•0 citations

Inversionless gain versus efficient gain: The autoionizing states configuration

Bruno Zambon

The absorption and stimulated emission of coherent electromagnetic radiation tuned close to an autoionizing state is investigated with the aim of clarifying some of the aspects behind the proposals of inversionless gain involving such atomic configurations. This is carried out within the framework of individual atomic evolution rather than by the use of density matrix equations, thus providing better insight into the fundamental processes of absorption and emission. In particular, we find that stimulated emission does not overcome absorption in spite of quantum interference of the Fano type being present. It is also shown that gain, in this configuration, although it can take place without population inversion between the involved levels, requires in any case a strong departure from thermal equilibrium conditions. Thereby a strong pumping mechanism, or equivalently a strong excitation power, is needed to reach the lasing threshold. This raises some questions on the relevance of the population inversion indicator of efficient gain implicitly assumed in similar configurations and in many related works.

Physical Review A•Jul 1, 1998•2 citations

Non-Reciprocity of Autoionizing Interferences: Lasers Without Inversion

Stephen E. Harris

Interferences of autoionizing lines may reduce or eliminate absorption of lower level atoms. Stimulated emission shows no such interferences, thereby allowing laser gain without population inversion.

Short Wavelength Coherent Radiation: Generation and Applications•Jan 1, 1988•0 citations

Gain with and without population inversion via vacuum-induced coherence in a V-type atom without external coherent driving

Weihua Xu, Jin‐Hui Wu, Jin-Yue Gao

In a three-level V-type atomic system without any external coherent driving, owing to the coherence that results from the vacuum of the radiation field, both the probe gain with and without population inversion can be achieved with very weak incoherent pumping. The gain is achieved in the absence of any external coherent driving field, so it is different from the gain without inversion in ordinary laser-driven schemes where a coherent driving field is necessary to create the coherence. The gain is also different from the conventional lasing gain because the population inversion is achieved via vacuum-induced coherence, which is dependent on the atomic coherence.

Journal of Physics B Atomic Molecular and Optical Physics•Mar 1, 2006•20 citations
We consider how externally coupled (e.g., dc-field-coupled) autoionizing states can be useful in producing gain without population inversion. The dc fields produce new absorption minima that enable one to obtain laser action in different frequency regions depending on the strength of the coupling. We calculate absorption and emission profiles assuming that one of the autoionizing states is incoherently pumped as in most conventional laser models. We present numerical results that demonstrate gain regions without population inversion.
We consider laser action on a transition involving an autoionizing state \ensuremath{\Vert}a〉 and an initially unpopulated state \ensuremath{\Vert}f〉, the population of which builds up because of spontaneous emission and Raman processes. The autoionizing state is pumped by a coherent field. We discuss the transient amplification of the probe field on the lasing transition for a range of parameters. The coherent field on the pumping transition leads to minima in the absorption spectra if the atomic population were in the state \ensuremath{\Vert}f〉. Such regions of minima can be used for obtaining gain even for long times.
The emergence of laser action from an atomic system without population inversion is beginning to attract theoretical and experimental attention as a possible way of generating useful coherent radiation at unusual wavelengths. The goal of this communication is to clarify the physical origin of this phenomenon using a four-level system whose ground state consists of two quasidegenerate levels that are coupled to a higher-lying state by a Raman-like transition. In the presence of the ground-state coherence induced by the Raman field, we calculate the absorption spectrum of a weak probe whose tunable frequency scans across the transition frequencies between the two ground-state levels and another higher-lying state that may or may not be weakly excited by an incoherent pump mechanism. Our calculation, based on a dressed atomic state approach, clarifies the conditions that must be satisfied to produce gain, identifies the frequency (or frequencies) at which the gain is maximum, and elucidates the functions of the incoherent pump, the Raman field, and the coherence between the ground-state levels in this process. An appropriate set of Maxwell- Bloch equations for a ring-cavity model of this system confirms the appearance of laser action when the small-signal gain conditions are satisfied.
We consider a four-level atomic system with a degenerate or quasidegenerate ground-state doublet and two excited states. One of the upper levels is coupled to the ground doublet by a coherent field of variable strength, which we refer to as the Raman field, whose role is to create atomic coherence between the driven atomic states. The other higher lying state is coupled to the ground states when laser action develops. This model includes an incoherent pump mechanism to create some population in the top lasing state. In appropriate conditions, for the incoherent pump rate and the Raman field strength, the absorption profile of the laser transition develops gain features. We discuss the physical origin of this gain which we find to be the consequence of a population inversion between dressed atomic states. It is interesting to compare the results of this analysis with a similar study of a three-level lambda system which was previously recognized to yield lasing without inversion.1 In this case the appearance of gain can be attributed to the induced atomic coherence.
The absorption and stimulated emission of coherent electromagnetic radiation tuned close to an autoionizing state is investigated with the aim of clarifying some of the aspects behind the proposals of inversionless gain involving such atomic configurations. This is carried out within the framework of individual atomic evolution rather than by the use of density matrix equations, thus providing better insight into the fundamental processes of absorption and emission. In particular, we find that stimulated emission does not overcome absorption in spite of quantum interference of the Fano type being present. It is also shown that gain, in this configuration, although it can take place without population inversion between the involved levels, requires in any case a strong departure from thermal equilibrium conditions. Thereby a strong pumping mechanism, or equivalently a strong excitation power, is needed to reach the lasing threshold. This raises some questions on the relevance of the population inversion indicator of efficient gain implicitly assumed in similar configurations and in many related works.
In a three-level V-type atomic system without any external coherent driving, owing to the coherence that results from the vacuum of the radiation field, both the probe gain with and without population inversion can be achieved with very weak incoherent pumping. The gain is achieved in the absence of any external coherent driving field, so it is different from the gain without inversion in ordinary laser-driven schemes where a coherent driving field is necessary to create the coherence. The gain is also different from the conventional lasing gain because the population inversion is achieved via vacuum-induced coherence, which is dependent on the atomic coherence.