Forced light scattering by broad-bandwidth incoherent pump lasers

Forced light scattering using broad-bandwidth incoherent pump light (${\lambda }_{\mathit{B}}$=508 nm, full width at half maximum Δ${\lambda }_{\mathit{B}}$=13.8 nm), and narrow-bandwidth probe light is investigated experimentally and compared with self-diffraction. Forced light scattering improves the dynamic range of measurement by an order of magnitude compared to self-diffraction. A theoretical analysis of this scheme is presented. The technique is used to measure the dephasing kinetics of solutions of crystal violet and bis-(dimethylamino)heptamethine. Resulting from the relatively large autocorrelation time of 40 fs, the experimental signals show no influence from inhomogeneous broadening of the absorption bands; the dephasing kinetics can be characterized by a dephasing time ${\mathit{T}}_2$≊10 fs and an intrinsic correlation time ${\mathrm{\tau }}_{\mathit{C}}$≊30 fs with a weak modulation (center frequencies ranging from 800 to 1200 ${\mathrm{cm}}^{\mathrm{-}1}$), which is attributed to a coherent motion of the molecule (vibration). The dephasing kinetics of crystal violet shows a close agreement with the dephasing kinetics of malachite green previously reported for two-pulse photon echoes with ultrashort pulses [P. C. Becker et al., Phys. Rev. Lett. 63, 505 (1989)].