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 quasi particle-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. The finite exciton-exciton interaction length is used to greatly reduce the computational effort. Applications arc made to coupled anharmonic vibrations in the amide I infrared band of peptides. Chirally sensitive and non-sensitive signals for α helices and antiparallel β sheets are compared.