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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

Lasers without inversion in quantum well intersubband transitions

Ataç İmamoğlu, Kenneth L. Campman, Hans‐Werner Schmidt, Rajeev J. Ram, Arthur C. Gossard

Published May 10, 1996• 0 citations
Publisher

Abstract

We propose a new class of intersubband lasers and amplifiers that achieve net gain without population inversion. The laser scheme is based on a unipolar semiconductor double quantum- well structure where gain occurs at a transition between conduction band subbands. In order to achieve net gain without inversion, we utilize Fano-type interferences. The semiconductor laser scheme that we are considering is analogous to the atomic lambda system that has been extensively analyzed in the context of electromagnetically induced transparency and lasing without inversion. A coherent coupling field however, is not required in the present scheme. The electronic coherence necessary for Fano-type interferences is established by resonant tunneling. For nonlinear optics applications, the asymmetry of the structure allows for (chi) (2) processes and therefore higher conversion efficiency or parametric gain.

DOI
10.1117/12.239474

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We propose a new class of intersubband lasers and amplifiers that achieve net gain without population inversion. The laser scheme is based on a unipolar semiconductor double quantum- well structure where gain occurs at a transition between conduction band subbands. In order to achieve net gain without inversion, we utilize Fano-type interferences. The semiconductor laser scheme that we are considering is analogous to the atomic lambda system that has been extensively analyzed in the context of electromagnetically induced transparency and lasing without inversion. A coherent coupling field however, is not required in the present scheme. The electronic coherence necessary for Fano-type interferences is established by resonant tunneling. For nonlinear optics applications, the asymmetry of the structure allows for (chi) (2) processes and therefore higher conversion efficiency or parametric gain.
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.
We report the observation of tunneling induced transparency in asymmetric double quantum well structures. Resonant tunneling through a thin barrier is used to coherently couple the two upper states in a three level system of electronic subbands in a GaAs/AlGaAs structure. This creates Fano-type interferences for the collective intersubband excitations in the absorption from the ground state, analogous to electromagnetically induced transparency (EIT) in atomic systems. We observe a 50% reduction in absorption between the subband resonances which can be explained by taking into account the coherent coupling of the upper states. We analyze the bias dependent absorption spectra and determine the relevant lifetime broadening and dephasing rates for the transitions.
Summary form only given. In this paper, we present coherent optical effects in a quantum well system with two electron subbands coupled by a pump laser. The Coulomb and light induced electronic renormalization is investigated with generalized density-functional theory. On the basis of the renormalized electron states, the absorption coefficient of a probe light beam is studied for intersubband transition by using a self-consistent field theory. Both the electromagnetically induced transparency (EMIT) and probe light amplification without population inversion are found.
This paper presents the current results of field-induced quantum interference in semiconductor quantum wells. Three-level systems with two conduction subbands in single and double quantum wells coupled by a resonant field are studied. We investigate effects of the Coulomb and field-induced electronic renormalizations of the energy subbands and steady eigenstates of electrons. The random-phase and ladder approximations have been used to calculate the linear interband and intersubband optical absorptions and refractive indices. The effect of collective dipole moment on the nonlinear susceptibility has been incorporated into the study by using a local-field approach. Lasing without population inversion, electromagnetically induced transparency, and enhanced nonlinearity with reduced absorption inside the intersubband-coupled single quantum well and dc-field coupled double quantum wells are found.
In a self-consistent field formalism we investigated the weak-probe optical intersubband response of a three-subband semiconductor quantum well pumped by a strong coherent laser beam. We showed that, when the pumping photon energy is somewhat above the energy separation between the two lowest subbands, a combination of hole-burning effects and coherent pump–probe wave interactions can lead to both optical gain without population inversion and an Autler–Townes-like doublet in the probe optical spectrum. These two absorption peaks, whose positions are blueshifted as the pump intensity is increased, are due to the two-photon absorption process and light-induced intersubband transitions between the two upper states. It is also demonstrated that, in a stepwise two-photon pumping scheme, the optical gain with population inversion can also occur in the quantum-well system when a modestly strong pump field is present.
We propose coherent control and enhancement of the refractive index with zero absorption in an n-type asymmetric double quantum well using intersubband transitions. These effects are caused by quantum coherence and interference whereby a strong infrared laser mixes upper conduction subbands of an intersubband transition with an auxiliary subband. In the ${\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}/\mathrm{A}\mathrm{l}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}$ system considered here, an approximately 10% enhancement of the refractive index accompanied with zero absorption occurs at 10.5 \ensuremath{\mu}m, when the system is driven by a 6.2-\ensuremath{\mu}m laser field with an intensity of \ensuremath{\sim}1 MW/cm2{\mathrm{M}\mathrm{W}/\mathrm{c}\mathrm{m}}^{2}MW/cm2. The interplay between quantum coherence and electron population dynamics not only causes an enhancement of refractive index similar to that in atomic systems, but can also induce both low positive and negative group velocities.