ELECTRONIC DEPHASING IN NONPOLAR ROOM-TEMPERATURE LIQUIDS - UV PHOTON-ECHO PULSE DURATION DEPENDENT MEASUREMENTS

The homogeneous dephasing times, T-2, were obtained for the nonpolar c hromophore diphenyl acetylene (DPA) dissolved in the room temperature nonpolar solvents 2-methyl pentane (2MP) and cyclohexane. The dephasin g times were determined by comparing the pulse duration dependent reso nant enhancement of the total two pulse four wave mixing signal to a n umerically evaluated theory. Data was taken with 80 and 400 fs transfo rm limited pulses at 300 nm, the electronic origin of DPA in the two s olvents. In DPA/2MP, T-2=120 fs and in DPA/cyclohexane, T-2=500 Ps. Th e analysis required concentration and power dependent measurements to quantitatively determine the resonant. enhancement of the signal arisi ng from the addition of DPA to the solvents above the nonresonant solv ent only signal. Fundamental experimental difficulties inherent in per forming UV femtosecond two pulse photon echoes, in particular the comp etition with nonresonant signal, are discussed. An efficient numerical algorithm for calculating photon echo decay curves with realistic pul se envelope is described. (C) 1997 American Institute of Physics.