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Journal of the Optical Society of America B

Practical aspects of optically coupled inversionless lasers

Jacob B. Khurgin, E. Rosencher

Published May 1, 1997• 10 citations
Publisher

Abstract

Conditions for gain and threshold of the inversionless laser are derived as a function of pump strength and relaxation rates. It is shown that lasing without inversion can be achieved most easily only in systems in which either conventional or Raman lasing is attainable. The threshold of the inversionless laser is shown to be orders of magnitude higher than that of the conventional laser. Practical implications, especially for intersubband lasers, are discussed.

DOI
10.1364/josab.14.001249

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Conference on Lasers and Electro-Optics•Aug 29, 2005•1 citation
Conditions for gain and threshold of the inversionless laser are derived as a function of pump strength and relaxation rates. It is shown that lasing without inversion can be achieved most easily only in systems in which either conventional or Raman lasing is attainable. The threshold of the inversionless laser is shown to be orders of magnitude higher than that of the conventional laser. Practical implications, especially for intersubband lasers, are discussed.
A rigorous density-matrix-based theory of lasing based on optically induced or autoionization-induced coherence between the levels is developed. The balance equations are obtained, and the conditions for lasing threshold are derived as a function of pumping strength and relaxation rates. Connection between the lasing without inversion and Raman and parametric processes is established. The main conclusion is that true CW lasing without inversion can indeed be obtained but only in a system where pumping and relaxation rates are favorable for attaining conventional lasing with population inversion. Practical implications of it, especially for the intersubband lasers, are discussed.
A rigorous density-matrix approach has been applied to the interaction between an autoionizing system and electromagnetic radiation. The balance equations have been derived and analytical expressions for the inversionless lasing threshold and saturation output have been obtained. Using the intersubband transitions as an example, the potential performance of the inversionless laser has been analyzed and found to be inferior to that of the conventional laser. \textcopyright{} 1996 The American Physical Society.
We analyze a laser system consisting of N closed three-level atoms confined in a single-mode cavity and derive the conditions for the onset of lasing without inversion or with inversion. We calculate the steady-state gain and lasing in the system and show that far above the lasing threshold, depending on the pumping and decay rates, the inversionless laser may operate in three different regimes, where the intensity of the laser depends linearly on N, is proportional to \ensuremath{\surd}N , or independent of N.
We show that a closed four-level system can exhibit lasing without population inversion in any state basis. The same system can be also made to exhibit lasing without population inversion in the bare-state basis but with population inversion in the dressed-state basis. We derive the conditions of lasing without inversion and examine the dependence of the gain on various system parameters. The lasing threshold and the steady-state photon numbers are calculated. Comparison with a ssV-type, three-level model is presented.
We propose a new scheme for lasing without population inversion that utilizes interferences in double-quantum-well intersubband transitions. In contrast to the previous inversionless laser schemes based on atomic systems, the new proposal permits us to use band-gap engineering to choose the subband energies, coupling strengths, and decay rates, as desired, and permits us to create a laser system that does not require population inversion. We present detailed calculations on a specific scheme and discuss possible extensions.
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.