The mechanism by which light is slowed through ruby has been the subject of great debate. To distinguish between the two main proposed mechanisms, we investigate the problem in the time domain by modulating a laser beam with a chopper to create a clean square wave. By exploring the trailing edge of the pulsed laser beam propagating through ruby, we can determine whether energy is delayed beyond the input pulse. The effects of a time-varying absorber alone cannot delay energy into the trailing edge of the pulse, as a time-varying absorber can only attenuate a coherent pulse. Therefore, our observation of an increase in intensity at the trailing edge of the pulse provides evidence for a complicated model of slow light in ruby that requires more than just pulse reshaping. In addition, investigating the Fourier components of the modulated square wave shows that harmonic components with different frequencies are delayed by different amounts, regardless of the intensity of the component itself. Understanding the difference in delays of the individual Fourier components of the modulated beam reveals the cause of the distortion the pulse undergoes as it propagates through the ruby.
A high-intensity laser pulse can lead to a change of the group index of a material, so that the pulse within that
material is slowed to only hundreds of meters per second. This kind of slow-light phenomenon scales with the
optical intensity of the pulse. While previous experiments have produced this effect with an elliptical beam
passing through a spinning ruby window, a question remains as to whether the effect would be present in a
circular beam. Here we use two different methods of producing slow light in a round beam, showing that, while
less pronounced than the effect with an elliptical beam, a slow-light effect can be seen in a round beam.
A spinning medium is predicted to induce a slight rotation in a transmitted image.
We amplify this effect by use of ruby as a slow light medium, giving image rotations of
several degrees. In terms of the orbital angular momentum such rotations are analogous to the
mechanical Faraday effect.