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Chinese Physics Letters

Reduction of Light Group Velocity by Coherent Population Oscillation in a Ruby Crystal

Zhang Yun-Dong, Bao-Hua Fan, Ping Yuan, Ma Zu-Guang

Published Jan 1, 2004• 13 citations
Publisher

Abstract

We report the investigation of the reduction of the group velocity propagation resulting from the steep change of the refractive index by the coherent population oscillation in a ruby crystal at room temperature. Slow light propagation is observed in a solid-state material at room temperature. The measured delay is about 2.314±0.005 ms, corresponding to a group velocity as slow as 43.215±0.094 m/s in a non-sinusoid modulated waveform. The influences of pulse duration on the delay and the reduction of light propagation are given.

DOI
10.1088/0256-307x/21/1/027

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We report the investigation of the reduction of the group velocity propagation resulting from the steep change of the refractive index by the coherent population oscillation in a ruby crystal at room temperature. Slow light propagation is observed in a solid-state material at room temperature. The measured delay is about 2.314±0.005 ms, corresponding to a group velocity as slow as 43.215±0.094 m/s in a non-sinusoid modulated waveform. The influences of pulse duration on the delay and the reduction of light propagation are given.
We have observed slow light propagation with a group velocity as low as 57.5+/-0.5 m/s at room temperature in a ruby crystal. A quantum coherence effect, coherent population oscillations, produces a very narrow spectral "hole" in the homogeneously broadened absorption profile of ruby. The resulting rapid spectral variation of the refractive index leads to a large value of the group index. We observe slow light propagation both for Gaussian-shaped light pulses and for amplitude modulated optical beams in a system that is much simpler than those previously used for generating slow light.
We have observed slow light propagation with a group velocity as slow as 27.52±0.05m/s in a ruby crystal at room temperature. The Gaussian-like pulse signal, which was gained by modulating beam at 514.5nm, was injected into a ruby crystal. The spectral hole effect, attributed to high laser power density, leads to the induced refractive index steep rising. According as this rising, the group velocity of pulse propagation in the ruby becomes very slowly. The experiment result shows that the velocity of pulse propagation depends on the modulation frequency, laser power, the position of crystal and the profile of signal waveform. At the same condition the Gaussian-like pulse obtains much slower velocity than sinusoidal signal.
We investigate the reduction of the group velocity propagation resulting from the steep change of the refractive index by the coherent population oscillation in erbium-doped optical fibre. The largest delay is measured to be about 8.75ms corresponding to a group index of 1.312 × 10 6 . The time delay or advancement depends on the pump intensity. Influences of the ion density on the fractional delay and the group velocity reduction of light propagation are studied. Based on our discussion the optimization parameters should be selected in order to obtain more appropriate time delay and the slowdown of group velocity.
We have observed both superluminal and ultraslow light propagation in an alexandrite crystal at room temperature. Group velocities as slow as 91 meters per second to as fast as -800 meters per second were measured and attributed to the influence of coherent population oscillations involving chromium ions in either mirror or inversion sites within the crystal lattice. Namely, ions in mirror sites are inversely saturable and cause superluminal light propagation, whereas ions in inversion sites experience conventional saturable absorption and produce slow light. This technique for producing large group indices is considerably easier than the existing methods to implement and is therefore suitable for diverse applications.