Theory for laser induced dichroism and its effect on absorption, fluorescence, and Raman spectra

Abstract

Conformational flexibility and its effect on the vibrationally resolved absorption and fluorescence spectra of oligofluorenes Appl.The theory is presented for a two beam pump and probe laser experiment where a strong pumping beam induces a saturated anisotropy in the distribution of ground and excited state molecules in solution. The probing laser beam is (i) tuned to another transition of the molecule, or (ii) used to induce nonresonant ground state Raman scattering. Formulas are given for the laser induced anisotropic absorption for the general case, where the directions of transition moments of the molecule for the absorption of pump and probe light form an angle anywhere between O' and 90'. Also, a comparison of the results to the existing theory for polarized fluorescence is made for weak intensity of the excitation source. Expressions are formulated for the polarization properties of the intensities of Raman bands modified by the presence of pumping light. The creation of the spatial anisotropy by the pump results in a Raman photoselection rule which permits one to distinguish asymmetric vibrational modes belonging to different representations of the same point group.

Structure studies of H2TMpyP4 and ZnTMpyP4 bound to DNA using laser-induced dichroism in solution

“…In the situation where the rotational correlation time of the molecule is longer than the pulse duration, the pump creates a spatial anisotropy in the distribution of ground is the angle between the electric vectors of the pump and the probe beams. An example of a theoretically calculated result based on eq 1 for a = 1 is shown in Figure 3a of ref 16.…”

Two-photon Absorbing Photonic Materials: From Fundamentals to Applications

“…The ESA spectra were obtained as a transient optical density, ∆D ||,⊥ = (k ||,⊥ · L)/ ln 10, where L = 1 mm (the path length of the cuvettes in all pump-probe measurements). The excited state absorption coefficients of the probe pulse, k(θ), for an arbitrary angle, θ, between the pump and probe polarization can be derived in the case of unsaturated absorption as [22,34]:…”

“…9). A comprehensive theoretical analysis of a two beam (pump and probe) laser experiment was performed [34], where a general case of induced saturated absorption anisotropy was considered. From this work, measurement of the absorption anisotropy of molecules in an isotropic ensemble facilitates the determination of the angle between the S 0 → S 1 (pump) and S 1 → S n (probe) transitions.…”

Molecular Orientations in Azopolymer Holographic Diffraction Gratings as Studied by Raman Confocal Microspectroscopy

“…Then, theories of laser-induced dichroism as largely developed in studies of the orientational statistics in liquid crystals − and in solutions , can be extended to the present case of anisotropic thin films.…”