title: Two-photon absorption cross section determination for fluorene derivatives: analysis of the methodology and elucidation of the origin of the absorption processes.
abstract: A comprehensive analysis of the well-known open aperture Z-scan method, using a modified equation for the change in transmittance, is presented and accounts for discrepancies in two-photon absorption (2PA) cross sections between picosecond and femtosecond excitation. This new approach takes into account excited-state absorption and stimulated emission of the molecules studied. The two-photon absorption cross-section spectra of a series of six fluorene-based derivatives, determined using picosecond pulses, over a broad spectral range (500-900 nm), and this approach using a modified fitting procedure in the open aperture Z-scan is reported. We demonstrate that the fluorene derivatives exhibit two-photon absorption cross-section values between 700 and 5000 GM, when excited into the two-photon allowed electronic state. Excitation anisotropy spectra, measured to investigate the nature of the observed linear and nonlinear absorption bands, are presented and provide insight into the 2PA process.
authors.affiliation: Department of Chemistry and CREOL, College of Optics and Photonics, University of Central Florida, PO Box 162366, Orlando, Florida 32816-2366, USA. belfield@mail.ucf.edu
authors.forename: Kevin D
authors.initials: KD
authors.lastname: Belfield
authors.forename: Mykhailo V
authors.initials: MV
authors.lastname: Bondar
authors.forename: Florencio E
authors.initials: FE
authors.lastname: Hernandez
authors.forename: Olga V
authors.initials: OV
authors.lastname: Przhonska
authors.forename: Sheng
authors.initials: S
authors.lastname: Yao
mesh_terms: D016880:Anisotropy; D005449:Fluorenes / Q000737:chemistry*; D015394:Molecular Structure; D017785:Photons; D012680:Sensitivity and Specificity; D013056:Spectrophotometry, Ultraviolet / Q000379:methods
chemical_list: D005449:Fluorenes