Observation of Ultraslow Light Propagation in a Ruby Crystal at Room Temperature

We have observed slow light propagation with a group velocity as low as $57.5\pm 0.5\mathrm{m}/\mathrm{s}$ 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.

Figure 1

The experimental setup used to observe slow light in ruby.

Figure 2

The relative modulation attenuation $A(\delta )$ with respect to the pump as a function of modulation frequency for input pump powers of 0.1 and 0.25 W. The solid lines represent the theoretical model of Eq. (10). The insets show the two coupling schemes discussed in the text.

Figure 3

Observed time delay as a function of the modulation frequency for input pump powers of 0.1 and 0.25 W. The solid lines represent the theoretical model of Eq. (9). The inset shows the normalized 60 Hz input (solid line) and output (dashed line) signal at 0.25 W. The signal was delayed $612\mu \mathrm{s}$ corresponding to an average group velocity of $118\mathrm{m}/\mathrm{s}$.

Figure 4

The normalized input and output intensities of a 5, 10, 20, and 30 ms pulse. The corresponding average group velocities of the pulses are 300, 159, 119, and $102\mathrm{m}/\mathrm{s}$. The inset shows a close-up of the 20 ms pulse.