Experimental Investigation of Three‐Level Optical Stark Effect in Semiconductors

Abstract

The three-level optical Stark effect is due to a dynamical coupling of two excited levels. The coupling is achieved by a high intensity CO, laser. Results of experiments on multiple quantum wells (MQW) and excitons in Cu,O are presented. In the MQW the coupling between the two lowest conduction band sublevels leads to characteristic changes in the one-photon spectra of the lowest exciton transitions. In Cu,O the CO, laser pulse couples 1 S and 2 P excitons. In this case the one-photon spectrum of the 2 P exciton (dipole allowed) and also of the 1 S spectrum (quadrupole allowed) show drastic changes. Most of the experimental results can be explained quantitatively in terms of a nonlinear susceptibility.Der optische Starkeffekt im Dreizustandssystem beruht auf der dynamischen Kopplung zweier angeregter Zustande. Die Kopplung wird mit einem hochintensiven C0,-Laser erreicht. Es werden experimentelle Ergebnisse an Quantentrogstrukturen (MQW) und Exzitonen in Cu,O vorgestellt. Im MQW fuhrt die Kopplung der beiden tiefsten Leitungsbandzustande zu charakteristischen Anderungen der Einphotonenspektren der tiefsten Exzitonubergange. In Cu,O koppelt der C0,-Laserpuls 1 Sund 2 P-Exzitonen. In diesem Fall zeigt das Einphotonenspektrum des 2 P-Exzitons (dipolerlaubt) wie auch das des 1 S-Exzitons (quadrupolerlaubt) drastische Anderungen. Der groDte Teil der experimentellen Ergebnisse kann quantitativ mittels einer nichtlinearen Suszeptibilitat erklart werden.') PF 500500, D-4600 Dortmund 50, FRG.

Realization of stripes and slabs in two and three dimensions

“…The question is to determine the ground state of the system, as the parameters J and p are varied. In some limiting cases, it is easy to identify the minimal energy states: e.g., if J is sufficiently small, the ground state is the Néel antiferromagnet, as one can prove by using reflection positivity [32]. If p > d + 1, there exists a critical value J c (p), of the form…”

Sum Rules for Nonlinear Optical Susceptibilities

“…They are extensions to nonlinear optics of the well-known TRK and ADNS sum rules and show that the nonlinear contributions vanish. The sum rule (21) was previously given by Peiponen 1171 for the model of the anharmonic oscillator.…”

“…We can adopt the same model but we impose that the sum rules (19) to (21) are verified and the asymptotic behaviour (14) and (15) is followed. The approximate expression for the total susceptibility is [19] , (24) N I(0l P P>I2 + hza;…”

“…2, where (24) gives the correct asymptotic behaviour, it is not appropriate for computing the correct value of the constant c, which appears in the sum rule (23). This is due to the fact that the contribution near the pole is extremely small because of the sum rule (21), and consequently the contributions from a large number of resonances are important. This suggests the usefulness of a realistic system where a complete set of states can be considered.…”

Polarization Dependence in the Intraband Optical Stark Effect of Quantum Wells

“…Since the optically coupled states involved belong to the same band to band transition this effect is termed "intraband" optical Stark effect [2]. In Cu,O this effect exhibits a characteristic polarization dependence [3]. The "interband" optical Stark effect was first observed in multiple quantum wells (MQW) [4].…”