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CRC Press eBooks

Optical nonlinearities and the Kerr-effect in phaseonium

U. Rathea, Michael Fleischhauer, Marlan O. Scully

Published Jul 16, 2021• 0 citations
Publisher

Abstract

Systems with atomic coherence can have interesting optical properties, such as non-absorbing resonances or an index of refraction at a frequency of vanishing absorption many orders of magnitude larger than is otherwise possible. This chapter shows that phaseonium can display a large nonlinear Kerr-effect near the atomic resonance while retaining complete transparency. Near resonance nonlinearities are usually accompanied by a large absorption of the medium. A three-level atom is initially prepared in a coherent superposition of the two lower levels. This can be achieved for example by a coherent pulse excitation. The Kerr-coefficient is defined as the coefficient of the first nonlinear correction to the index of refraction.

DOI
10.1201/9781003209638-2

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Systems with atomic coherence can have interesting optical properties, such as non-absorbing resonances or an index of refraction at a frequency of vanishing absorption many orders of magnitude larger than is otherwise possible. This chapter shows that phaseonium can display a large nonlinear Kerr-effect near the atomic resonance while retaining complete transparency. Near resonance nonlinearities are usually accompanied by a large absorption of the medium. A three-level atom is initially prepared in a coherent superposition of the two lower levels. This can be achieved for example by a coherent pulse excitation. The Kerr-coefficient is defined as the coefficient of the first nonlinear correction to the index of refraction.
. We investigate the possibility of enhancing the refractive properties in a nonabsorbing medium via two fundamentally different schemes. First there is the coherent preparation of three-level atoms where absorption is cancelled due to destructive interference while the refractivity is not hampered in the same way. There also is the possibility of cancelling absorption via a mixture of absorbing and emitting two-level atoms without the need of a coherent preparation. One drawback here, however, is high sensitivity to Doppler broadening, collisions and number fluctuations which makes this scheme practically infeasible. Introduction The various application of atomic coherence in laser physics and quantum optics has recently attracted considerable interest. It has been shown that atomic coherence can lead to absorption cancellation (Alzetta, et al., 1976; and Gray, et al., 1979) and quenching of spontaneous emission noise (Scully, 1985). More recently, the notion of noninversion lasing has received attention, and it was shown that atomic coherence leading to cancellation of absorption does not necessarily influence emission (Harris, 1989; Scully, et al., 1989; and Kocharovskaya and Khanin, 1988). There has been extensive research on many schemes that involve coherence between an upper or lower level laser doublet due to various means: microwave or Raman coherent coupling and spontaneous and incoherent pumping coupling just to name the most important.
We show that long-lived bright Zeeman coherence that is responsible for absorption enhancement and steep anomalous dispersion in an atomic medium gives rise to a giant nonlinearity of the atomic susceptibility, in a similar manner to the dark coherence responsible for the well-known electromagnetically induced transparency. The intensity dependent refractive index of Cs vapour with a ground state Zeeman coherence in the vicinity of the D2 resonance line has been measured at low light intensity. The Kerr nonlinearity in the bright coherent state (n2 approx 1.0 × 10-6 cm2 mW-1) is higher than that in a dark state under the same experimental conditions. Higher order nonlinear components of the refractive index have also been estimated for both coherent states.
We report an experimental observation of large Kerr nonlinearity with vanishing linear susceptibilities in coherently prepared four-level rubidium atoms. Quantum coherence and interference manifested by electromagnetically induced transparency suppress the linear susceptibilities and greatly enhance the nonlinear susceptibilities at low light intensities. The measured Kerr nonlinearity is comparable in magnitude to the linear dispersion in a simple two-level system and is several orders of magnitude greater than the Kerr nonlinearity of a conventional three-level scheme under similar conditions.