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Physical Review A

Feasibility of lasing without inversion in the two-level system with split upper levels coupled by microwave radiation

Victor R. Blok, Gennady M. Krochik

Published May 1, 1991• 2 citations

Abstract

Zhu, Cresser, and Fearn [preceding Comment, Phys. Rev. A 43, 5170 (1991)] give an erroneous formal proof that lasing without inversion in the system with two upper optically identical levels is impossible. Their approach has little to do with the case of two close but different, well-separated split levels, considered in our previous paper [Blok and Krochik, Phys. Rev. A 41, 1517 (1990)]. It is evident even without laborious calculation that lasing without inversion is impossible in the system of indistinguishable levels, considered by Zhu, Cresser, and Fearn, because one cannot provide the interference among identical transitions. Their formal proof is, in addition, incorrect because they apply a steady-state approximation to the conditions where it is not valid; the transient response of the medium must be calculated instead. We also used the steady-state approximation in our previous paper, but very cautiously, in a domain where it is valid to obtain some analytical formulas, which proved to be qualitatively correct under the transient response approach [Blok and Krochik (unpublished)].

DOI: 10.1103/physreva.43.5173

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Comment on ‘‘Theory of lasers without inversion’’

Shi-Yao Zhu, James D. Cresser, H. Fearn

We prove that lasing without inversion is impossible in the three-level system with two active upper levels that are mixed by applied low-frequency electromagnetic radiation. Such lasing was recently proposed by Blok and Krochik [Phys. Rev. A 41, 1517 (1990)].

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Lasing without inversion: Theory of transient behavior

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Reply to ‘‘Comment on ‘Lasing without inversion in a V system due to trapping of modified atomic states’ ’’

Weihan Tan, Weiping Lu, Robert G. Harrison

Accounting for the mistake in our earlier analysis [Phys. Rev. A 46, R3613 (1992)] that was pointed out by Zhu and Xiao [recent Comment, Phys. Rev. A 49, 2203 (1994)] we show that lasing without inversion is still achieved in our more general model description of a ssV-shaped system.

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

V. Ahufinger, J. Mompart, R. Corbalán

Summary form only given. We study a model for an incoherently pumped laser operating with a Doppler-broadened three-level system placed in a doubly resonant cavity and producing two laser fields, one of them without population inversion. Each laser field couples to only one of the transitions of the three-level medium. We have studied our model for parameters appropriate to two real atomic systems (i) a cascade scheme in atomic /sup 138/Ba looking for lasing with (without) inversion at /spl lambda//sub /spl beta//=554 nm (/spl lambda//sub /spl alpha//=821 nm), and (ii) a V-scheme in atomic /sup 85/Rb with ordinary lasing at /spl lambda//sub /spl alpha//=780 nm and lasing without inversion (LWI) at /spl lambda//sub /spl alpha//=4216 nm. These two cases are qualitatively different in that two-photon processes are responsible for inversionless gain in case (i) while LWI in case (ii) arises from one-photon processes. Moreover, the frequency up-conversion ratio is R=0.67 for the case of /sup 138/Ba and it is R=1.88 for the case of /sup 85/Rb. In spite of the fact that the frequencies of the two laser fields are relatively different, our results show that dual-wavelength lasing extends up to Doppler broadening values typical for optical transitions of atoms in a vapor cell. In case (i) /spl alpha/-lasing occurs without two-photon inversion only for approximately the lower half of the domain of Doppler-broadening values. However, in case (ii) one has LWI in all the domains. Some considerations for a practical realization of the dual-wavelength inversionless-conventional laser are discussed.

Conference on Lasers and Electro-Optics•Aug 29, 2005•1 citation

Theory of lasers without inversion

Victor R. Blok, Gennady M. Krochik

We here present the theory of lasing without inversion for systems with a split upper laser level. We show that the effect of amplification without inversion may be realized for at least two different situations. In the first situation, the effect is due to the asymmetry of radiative characteristics of quasidegenerate transitions. In the second situation, the effect can be provided without any asymmetry and is achievable for the definite phase of the transfer of coherence between the quasidegenerate levels (quasiparametric amplification). We also show that for laser amplification without inversion, the rate (frequency) of mixing of the quasidegenerate levels should be significantly higher than the linewidths of these levels. This mixing of quasidegenerate levels can be realized by low-frequency electromagnetic radiation or by interaction with an auxiliary third level. In addition, we derive the conditions for providing laser action for such systems rigorously, and we give some specific examples for the realization of this effect in gaseous and solid-state media. One of the most promising configurations may be realized in solid-state media when two narrow quasidegenerate levels are embedded in quasifree states (low-density state conduction band). We also discuss the use of a parametric mechanism for the creation of spatial gratings and for the construction of new types of electro-optical devices.

Physical Review A•Feb 1, 1990•44 citations

Comment on ‘‘Lasing without inversion in a V system due to trapping of modified atomic states’’

Yifu Zhu, Min Xiao

We point out a mistake in a recent paper [Tan, Lu, and Harrison, Phys. Rev. A 46, R3613 (1992)] and show that, contrary to the authors' claim, lasing without inversion is impossible in a closed V system driven by a single coherent field only.

Physical Review A•Mar 1, 1994•9 citations

Zhu, Cresser, and Fearn [preceding Comment, Phys. Rev. A 43, 5170 (1991)] give an erroneous formal proof that lasing without inversion in the system with two upper optically identical levels is impossible. Their approach has little to do with the case of two close but different, well-separated split levels, considered in our previous paper [Blok and Krochik, Phys. Rev. A 41, 1517 (1990)]. It is evident even without laborious calculation that lasing without inversion is impossible in the system of indistinguishable levels, considered by Zhu, Cresser, and Fearn, because one cannot provide the interference among identical transitions. Their formal proof is, in addition, incorrect because they apply a steady-state approximation to the conditions where it is not valid; the transient response of the medium must be calculated instead. We also used the steady-state approximation in our previous paper, but very cautiously, in a domain where it is valid to obtain some analytical formulas, which proved to be qualitatively correct under the transient response approach [Blok and Krochik (unpublished)].

Summary form only given. We study a model for an incoherently pumped laser operating with a Doppler-broadened three-level system placed in a doubly resonant cavity and producing two laser fields, one of them without population inversion. Each laser field couples to only one of the transitions of the three-level medium. We have studied our model for parameters appropriate to two real atomic systems (i) a cascade scheme in atomic /sup 138/Ba looking for lasing with (without) inversion at /spl lambda//sub /spl beta//=554 nm (/spl lambda//sub /spl alpha//=821 nm), and (ii) a V-scheme in atomic /sup 85/Rb with ordinary lasing at /spl lambda//sub /spl alpha//=780 nm and lasing without inversion (LWI) at /spl lambda//sub /spl alpha//=4216 nm. These two cases are qualitatively different in that two-photon processes are responsible for inversionless gain in case (i) while LWI in case (ii) arises from one-photon processes. Moreover, the frequency up-conversion ratio is R=0.67 for the case of /sup 138/Ba and it is R=1.88 for the case of /sup 85/Rb. In spite of the fact that the frequencies of the two laser fields are relatively different, our results show that dual-wavelength lasing extends up to Doppler broadening values typical for optical transitions of atoms in a vapor cell. In case (i) /spl alpha/-lasing occurs without two-photon inversion only for approximately the lower half of the domain of Doppler-broadening values. However, in case (ii) one has LWI in all the domains. Some considerations for a practical realization of the dual-wavelength inversionless-conventional laser are discussed.

We here present the theory of lasing without inversion for systems with a split upper laser level. We show that the effect of amplification without inversion may be realized for at least two different situations. In the first situation, the effect is due to the asymmetry of radiative characteristics of quasidegenerate transitions. In the second situation, the effect can be provided without any asymmetry and is achievable for the definite phase of the transfer of coherence between the quasidegenerate levels (quasiparametric amplification). We also show that for laser amplification without inversion, the rate (frequency) of mixing of the quasidegenerate levels should be significantly higher than the linewidths of these levels. This mixing of quasidegenerate levels can be realized by low-frequency electromagnetic radiation or by interaction with an auxiliary third level. In addition, we derive the conditions for providing laser action for such systems rigorously, and we give some specific examples for the realization of this effect in gaseous and solid-state media. One of the most promising configurations may be realized in solid-state media when two narrow quasidegenerate levels are embedded in quasifree states (low-density state conduction band). We also discuss the use of a parametric mechanism for the creation of spatial gratings and for the construction of new types of electro-optical devices.