Photon echo experiments measure optical dephasing times. However, a more detailed characterization of system-bath interactions can be obtained using the three pulse photon echo peak shift (3PEPS) technique. The system-bath interactions are embedded in the nuclear transition frequency correlation function, M(t). The relationship between the peak shift measurements and M(t) is shown for the impulsive limit. The applicability of this technique with finite pulse duration is demonstrated through various simulations. Using photon echo peak shift measurements, the solute- solvent interactions of infrared laser dyes, IR144 and DTTCI, in organic polymer glasses, polymethylmethacrylate (PMMA) and polyvinylformal (PVF), are studied. The inertial motion dominates the solute-solvent interactions, and the diffusive motion, which shows the characteristics of the solvent, is frozen and manifests itself as the inhomogeneity in these glassy systems. This study shows that the inhomogeneity of a glassy system is temperature independent. In addition, the harmonic bath model is shown to describe the glassy systems very well. The B820 subunit of light harvesting 1 complex (LH1) of Rhodospirillum rubrum is also studied using the peak shift measurements. By comparing the peak shift data of LH1 to the B820 subunit, the time scale of energy transfer within the LH1 ring is determined to be ~100 fs, and the mechanism which modulates the peak shifts caused by energy transfer is explained. Furthermore, the excitonic length of LH1 is determined to be roughly over two Bacteriochlorophylls. One problem with 3PEPS is the inability to completely characterize the initial decay of M(t). That is, 3PEPS cannot be used to distinguish whether the system-bath interactions are described by the Kubo model or the multi-mode Brownian oscillator model. The fifth-order three pulse photon echo (F3PE) technique has the ability to distinguish these models. F3PE signals of IR144 and DTTCI in various polar solvents have been measured. The preliminary F3PE data and all of the 16 response functions responsible for F3PE signals are presented.
- Pub Date:
- September 1997
- Chemistry: Physical, Physics: Optics, Chemistry: Biochemistry, Biophysics: General, Biology: Plant Physiology