Electronic dephasing in nonpolar room temperature liquids: UV photon echo pulse duration dependent measurements

The homogeneous dephasing times, T2 , were obtained for the nonpolar chromophore diphenyl acetylene ~DPA! dissolved in the room temperature nonpolar solvents 2-methyl pentane ~2MP! and cyclohexane. The dephasing times were determined by comparing the pulse duration dependent resonant enhancement of the total two pulse four wave mixing signal to a numerically evaluated theory. Data was taken with 80 and 400 fs transform limited pulses at 300 nm, the electronic origin of DPA in the two solvents. In DPA/2MP, T25120 fs and in DPA/cyclohexane, T25500 fs. The analysis required concentration and power dependent measurements to quantitatively determine the resonant enhancement of the signal arising from the addition of DPA to the solvents above the nonresonant solvent only signal. Fundamental experimental difficulties inherent in performing UV femtosecond two pulse photon echoes, in particular the competition with nonresonant signal, are discussed. An efficient numerical algorithm for calculating photon echo decay curves with realistic pulse envelope is described. © 1997 American Institute of Physics. @S0021-9606~97!00618-1#