Collective Oscillator Research Articles

Two-exciton spectroscopy of photosynthetic antenna complexes: Collective oscillator analysis

The linear and third-order polarizabilities of the light-harvesting antennae of photosynthetic bacteria and green plants are calculated using an equation of motion approach which maps the system onto a coupled set of anharmonic excitonic oscillators. The oscillator representation is shown to have several advantages over the traditional picture based on properties of individual global eigenstates of the aggregate; besides a considerable reduction of computational effort, the dynamics of excitations in the two-exciton band is conveniently analyzed in terms of single-exciton Green’s functions and the two-exciton scattering matrix.

Multiple scattering by finite regular arrays of resonators

Earlier results for multiple scattering by arbitrary configurations of N obstacles are applied to seven regular arrays of two to six monopole resonators (with radius a, maximum scattering cross section σc, and normalized resonance frequency xc=kca). The arrays involve m=1, 2, or 3 different values of the separations of monopole centers, with d as the smallest. For each array, the corresponding scattering amplitude reduces to a sum of m+1 collective oscillator modes Fn (orthogonal in the same sense as the spherical harmonics). The doublet, triangular, and tetrahedral arrays are specified by two modes, F0 and F1; the square, pentagonal, and octahedral arrays require a third, F2; and the hexagonal array also requires a fourth, F3. The scattering cross section S of each array is less than 2Nσc, with maximum at a frequency ka=x near xc for relatively large kd=y=x/p≫x. If y>2x is small, the Fn reduce to simple multipoles in terms of spherical harmonics and elementary functions of x, p, and xc. Then S has narrow...