We report on the generation of various hole-centered beams in the focal region of a lens and investigate their effectiveness to break the diffraction barrier in fluorescence microscopy by stimulated emission. Patterning of the phase of the stimulating beam across the entrance pupil of the objective lens produces point-spread-functions with twofold, fourfold, and circular symmetry, which narrow down the focal spot to 65-100 nm. Comparison with high-resolution confocal images exhibits a resolution much beyond the diffraction barrier. Particles that are only 65-nm apart are resolved with focused light.
We present a comprehensive experimental and theoretical study of the optical properties of matrix-isolated molecules of the two perylene derivatives N , NЈ-dimethylperylene-3,4,9,10-dicarboximide ͑MePTCDI͒ and 3,4,9,10-perylenetetracarboxylic dianhydride ͑PTCDA͒. A solid solution of the dyes in an SiO 2 matrix exhibits monomer-like behavior. Transient absorption pump-probe spectroscopy in the range 1.2-2.6 eV has been performed on an ultrafast time scale. The differential transmittance reveals contributions from ground-state bleaching, stimulated emission, and excited-state absorption. Both systems exhibit broad excited-state absorption features below 2.0 eV with a clear peak around 1.8 eV. The spectra can be consistently explained by the results of quantum-chemical calculations. We have applied both the coupled cluster singles and doubles ͑CCSD͒ model and the multireference-determinant single and double configuration-interaction ͑MRD-CI͒ technique on the basis of the intermediate neglect of differential overlap ͑INDO͒ Hamiltonian. The results are insensitive to whether the geometry is optimized for the electronic ground state or first excited state. The experimental polarization anisotropies for the two major transitions are in agreement with the calculated polarizations.
We present a comprehensive study of ultrafast relaxation properties of optical excitations in thin films of quasi-1D stacked organic materials PTCDA (3,4,9,10-perylenetetracarboxylic dianhydride) and MePTCDI (N,N'-dimethylperylene-3,4,9,10-dicarboximide) over five decades of time. Pump-probe experiments reveal excitonic intraband relaxation time constants of 65 fs for MePTCDI and 100 fs for PTCDA. The initial time-resolved luminescence anisotropy is consistent with the exciton model of Davydov-split states. The subsequent decay of the anisotropy can be explained with a thermally activated exciton hopping process. A full understanding of the pump-probe experiments calls for an explanation beyond the models presently available.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.