Spectral hole-burning and slow light in emerald and ruby

Abstract

The temperature dependence of the Ri line of Chatham laboratory grown emeralds (Be3AI2(Si03)6) containing low concentrations of chromium (III) (0.04% and 0.0017% per weight) is investigated in the temperature range of 2.5 - 260 K by spectral hole-burning, luminescence line narrowing experiments and luminescence spectroscopy. The contribution to the homogeneous linewidth at 6 K is 70 kHz and over 400 GHz at 260 K. The data is well described by the two-phonon Raman process above 80 K. Below 80 K, the direct process between the two 2E levels is dominant. However, at temperatures below 10 K a low energy phonon is required to explain the temperature dependence. The generation of slow light by transient hole-burning is reported for the first time. A Gaussian probe pulse is propagated in an optically dense medium provided by the Ri(±3/2) line of 130 ppm Bagdasarov ruby. A delay of 10.8 ns is observed, corresponding to a reduction of the group velocity of 213000 m/s which is a reduction by a factor of 1400 compared to air.