Effect of buffer gas on an electromagnetically induced transparency in a ladder system using thermal rubidium vapor

We report on the observation of electromagnetically induced transparency in a ladder system in the presence of a buffer gas. In particular, we study the 5S(1/2)-5P(3/2)-5D(5/2) transition in thermal rubidium vapor with a neon buffer gas at a pressure of 6 Torr. In contrast to the line-narrowing effect of buffer gas on A systems, we show that the presence of the buffer gas leads to an additional broadening of (34 +/- 5) MHz, which suggests a cross section for Rb(5D(5/2))-Ne of sigma((D))(k) = (23 +/- 4) x 10(-19) m(2). However, in the limit where the coupling Rabi frequency is larger than the collisional dephasing, a strong transparency feature can still be observed.