Measurement of ultrafast dephasing time of Cresyl Fast Violet in cellulose by photon echoes with incoherent light

Abstract

Ultrafast homogeneous transverse relaxation time (dephasing time) T2 of Cresyl Fast Violet in cellulose has been measured in the S0 ↔ S1 transition by photon echoes with temporally incoherent nanosecond laser pulses. At 10 K, T2 was 0.7 psec when the sample was excited 6250 Å near the long-wavelength edge of the absorption band, but it was several tens of femtoseconds at 5940 Å. The fact that T2 is shorter at shorter wavelengths can attributed to the intramolecular relaxation of Cresyl Fast Violet molecules. T2 was measured also at 80 and 300 K. At 10 K persistent nonphotochemical holes (PNPH’s) were observed, and the relations between T2 and the shapes of the PNPH’s have been considered.