Photon echoes and persistent hole burning in organic amorphous systems

The dephasing time T₂ of cresyl violet in polyvinyl alcohol (PVA) was measured by photon echoes with temporally incoherent nanosecond pulses. In the echo decay curve we observed a slowly decaying wing whose decay constant agrees reasonably well with the width of the persistent hole at the tail of a sharp peak near zero-delay time. When the intensity of the excitation pulses was reduced the wing became prominent relative to the sharp peak. We believe that the slowly decaying wing is due to the zero-phonon line absorption and the sharp peak near zero-delay time originates from the phonon-sideband absorption. We also observed the echo decay curves at several temperatures between 6 and 19 K. The dephasing time T₂ obtained by the preliminary measurements seems to fit a T^-1.3 temperature law.