Phys.org December 21, 2024
When a pulse of light traverses a material, it incurs group delay. Should the group delay experienced by photons be attributed to the time they spend as atomic excitations? However reasonable this connection may seem, it appears problematic when the frequency of the light is close to the atomic resonance, as the group delay becomes negative in this regime. An international team of researchers (Canada, Australia) used the cross-Kerr effect to probe the degree of atomic excitation caused by a resonant transmitted photon, by measuring the phase shift on a separate beam that was weak and off-resonant. Over a range of pulse durations and optical depths their results were consistent with the recent theoretical prediction that the mean atomic excitation time caused by a transmitted photon equals the group delay experienced by the light. They measured mean atomic excitation times for the most narrowband pulse for the most broadband pulse. According to the researchers their results suggest that negative values taken by times such as the group delay have more physical significance than has generally been appreciated… read more. Open Access TECHNICAL ARTICLEÂ [not peer reviewed]