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Laser Physics

Electromagnetically-induced transparency and slow light in room temperature 4He*

Joyee Ghosh, Fabienne Goldfarb, J.-L. Le Gouët, Fabien Bretenaker, Rupamanjari Ghosh

Published Apr 2, 2010• 0 citations
Publisher

Abstract

Electromagnetically-induced transparency (EIT) in three-level Λ-systems is based on quantum interference effects involving coherence between the two lower levels, which allow propagation of a resonant probe light beam in the presence of a strong coupling field. We have observed transparency in ultra-narrow (<10 kHz) windows at the resonant 1.083 μm transition for purely electronic spins in gaseous 4 He* at room temperature. Slow light is an interesting outcome of the EIT phenomenon due to extreme dispersion within the narrow transparency window. We have obtained group delays of about 4 μs in a 2.5 cm long He* cell. A complete theoretical analysis explains our observations emphasizing the positive role of collisions. Slow light with 1-GHz Doppler broadening opens the door to applications of controllable large-bandwidth delays in radars.

DOI
10.1134/s1054660x10090070

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Electromagnetically-induced transparency (EIT) in three-level Λ-systems is based on quantum interference effects involving coherence between the two lower levels, which allow propagation of a resonant probe light beam in the presence of a strong coupling field. We have observed transparency in ultra-narrow (<10 kHz) windows at the resonant 1.083 μm transition for purely electronic spins in gaseous 4 He* at room temperature. Slow light is an interesting outcome of the EIT phenomenon due to extreme dispersion within the narrow transparency window. We have obtained group delays of about 4 μs in a 2.5 cm long He* cell. A complete theoretical analysis explains our observations emphasizing the positive role of collisions. Slow light with 1-GHz Doppler broadening opens the door to applications of controllable large-bandwidth delays in radars.
4 He ∗ at room temperature is a particularly interesting system as velocity changing collisions (VCCs) are necessary to observe ultra-narrow (less than 10 kHz) EIT windows for purely electronic spins in the presence of Doppler broadening. Such narrow resonances are known to be linked to a dramatic reduction of the group velocity of a probe pulse, although the medium is transparent. The evolution of the delay is recorded with respect to the coupling beam intensity and to small Raman detunings. We also demonstrate that it is possible to use optically detuned resonances ( Fano-like profiles ) to see a transition from slow light to negative group velocity. All these measurements are found to be in good agreement with a simple model based on an effective homogeneous linewidth.
Abstract Electromagnetically induced transparency (EIT) in five-level atomic systems is theoretically investigated for three representative configurations: M-, inverted-Y, and K-type systems driven by a weak probe field and three control laser fields. The different coupling schemes produce different quantum interference pathways and two-photon resonance conditions, leading to markedly different EIT spectra. The M-type configuration exhibits one, two, and three well-resolved transparency windows as successive control fields are introduced. In contrast, the inverted-Y configuration produces broader transparency windows because of the overlap of multiple interference channels, whereas the K-type configuration exhibits only a single EIT window when all control fields are resonant. Multiple transparency windows in the K-type system appear after introducing appropriate coupling-field detunings. Doppler broadening at room temperature significantly broadens the absorption spectrum and reduces the transparency depth, while preserving the number and positions of the EIT windows. These results demonstrate that the coupling scheme plays an important role in determining the formation and evolution of multi-window EIT spectra and identify the characteristics of the three five-level configurations for multi-channel quantum-optical applications, as well as for the experimental observation of EIT spectra in five-level configurations.
Controlling the optical response of a medium through suitably tuned coherent electromagnetic fields is highly relevant in a number of potential applications, from all-optical modulators to optical storage devices. In particular, electromagnetically induced transparency (EIT) is an established phenomenon in which destructive quantum interference creates a transparency window over a narrow spectral range around an absorption line, which, in turn, allows to slow and ultimately stop light due to the anomalous refractive index dispersion. Here we report on the observation of a new form of both induced transparency and amplification of a weak probe beam in a strongly driven silicon photonic crystal resonator at room temperature. The effect is based on the oscillating temperature field induced in a nonlinear optical cavity, and it reproduces many of the key features of EIT while being independent of either atomic or mechanical resonances. Such thermo-optically induced transparency will allow a versatile implementation of EIT-analogs in an integrated photonic platform, at almost arbitrary wavelength of interest, room temperature and in a practical, low cost, and scalable system.
In this paper, we study the formation of two electromagnetically induced transparency (EIT) windows in a four-level lambda atomic system with Doppler broadening. The depth and the width of the EIT windows are easily changed by adjusting the intensity of the controlling laser fields. Meanwhile, the position of the EIT windows is also easily shifted by changing the frequency of the laser fields. In particular, by turning on or off one of the two coupling laser fields, the probe field response can be switched between one or two EIT window regimes, i.e., it is possible to switch between absorption and transparency regimes, and vice versa. In addition, our analytical model also allows one to investigate the influence of temperature (or Doppler width) on EIT windows, which is necessary for experimental observations as well as related applications at room temperature.