We have measured with 0.5-psec resolution the reshaping of small-area 7-psec laser pulses to $0\pi$ pulses due to their passage through an optically thick sodium cell. The reshaped pulses have a picosecond oscillatory structure characteristic of $0\pi$ pulses that extends over more than 100 psec. These observations are compared in detail with the predictions of theory and good agreement is obtained

• Received 14 May 1984

DOI:https://doi.org/10.1103/PhysRevLett.53.552