12 research outputs found
Final Generalization of the Three Coupled Oscillator Model in the Crystal Optical Activity
In this paper we generalize the quantum mechanical model of three coupled
oscillators because of its usage in the crystal optical activity. Using this
model we can include the influence of all essential couplings between single
oscillators which represent the molecules or atoms of optically active crystals
belonging for example to the space groups of symmetry D(3,4) or D(3,6). The
single oscillators are damped and therefore we can include both parts of the
optical activity - optical rotatory dispersion and circular dichroism - into
computations. We present more universal formulas for description of the above
mentioned parts.Comment: 12 pages, LaTeX 2.0.
Frenkel Excitons in Random Systems With Correlated Gaussian Disorder
Optical absorption spectra of Frenkel excitons in random one-dimensional
systems are presented. Two models of inhomogeneous broadening, arising from a
Gaussian distribution of on-site energies, are considered. In one case the
on-site energies are uncorrelated variables whereas in the second model the
on-site energies are pairwise correlated (dimers). We observe a red shift and a
broadening of the absorption line on increasing the width of the Gaussian
distribution. In the two cases we find that the shift is the same, within our
numerical accuracy, whereas the broadening is larger when dimers are
introduced. The increase of the width of the Gaussian distribution leads to
larger differences between uncorrelated and correlated disordered models. We
suggest that this higher broadening is due to stronger scattering effects from
dimers.Comment: 9 pages, REVTeX 3.0, 3 ps figures. To appear in Physical Review
Time-domain chirally-sensitive three-pulse coherent probes of vibrational excitons in proteins
The third order optical response of bosonic excitons is calculated using the
Green's function solution of the Nonlinear Exciton Equations (NEE) which
establish a quasiparticle-scattering mechanism for optical nonlinearities. Both
time ordered and non ordered forms of the response function which represent
time and frequency domain techniques, respectively, are derived. New components
of the response tensor are predicted for isotropic ensembles of periodic chiral
structures to first order in the optical wavevector. The nonlocal nonlinear
response function is calculated in momentum space, where the finite
exciton-exciton interaction length greatly reduces the computational effort.
Applications are made to coupled anharmonic vibrations in the amide I infrared
band of peptides. Chirally-sensitive and non sensitive signals for alpha
helices and antiparallel beta sheets are compared.Comment: 26 pages, 6 figure
Fluorescence decay in aperiodic Frenkel lattices
We study motion and capture of excitons in self-similar linear systems in
which interstitial traps are arranged according to an aperiodic sequence,
focusing our attention on Fibonacci and Thue-Morse systems as canonical
examples. The decay of the fluorescence intensity following a broadband pulse
excitation is evaluated by solving the microscopic equations of motion of the
Frenkel exciton problem. We find that the average decay is exponential and
depends only on the concentration of traps and the trapping rate. In addition,
we observe small-amplitude oscillations coming from the coupling between the
low-lying mode and a few high-lying modes through the topology of the lattice.
These oscillations are characteristic of each particular arrangement of traps
and they are directly related to the Fourier transform of the underlying
lattice. Our predictions can be then used to determine experimentally the
ordering of traps.Comment: REVTeX 3.0 + 3PostScript Figures + epsf.sty (uuencoded). To appear in
Physical Review