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The article describes a newly discovered single-beam heterodyne Z-scan method, which is commonly being used for the measurement of the slow response nonlinear refraction of absorbers exhibiting excellent sensitivity. The different parasitic linear effects can be easily eliminated by increasing the sensitivity of the absorbers.

We report experimental and theoretical studies of the two-photon absorption spectrum of two nitrofuran derivatives: nitrofurantoine, (1-(5-nitro-2-furfurilideneamine)-hidantoine) and quinifuryl, 2-(5′-nitro-2′-furanyl)ethenyl-4-{N-[4′-(N,N-diethylamino)-1′-methylbutyl]carbamoyl} quinoline. Both molecules are representative of a family of 5-nitrofuran-ethenyl-quinoline drugs that have been demonstrated to display high toxicity to various species of transformed cells in the dark. We determine the two-photon absorption cross-section for both compounds, from 560 to 880 nm, which present peak values of 64 GM for quinifuryl and 20 GM for nitrofurantoine (1 GM = 1×10-50cm4.s.photon-1). Besides, theoretical calculations employing the linear and quadratic response functions were carried out at the density functional theory level to aid the interpretations of the experimental results. The theoretical results yielded oscillator strengths, two-photon transition probabilities, and transition energies, which are in good agreement with the experimental data. A higher number of allowed electronic transitions was identified for quinifuryl in comparison to nitrofurantoine by the theoretical calculations. Due to the planar structure of both compounds, the differences in the two-photon absorption cross-section values are a consequence of their distinct conjugation lengths. [ABSTRACT FROM AUTHOR]

The study of excited state properties of chlorophyll a is a subject of foremost interest, given that it plays important roles in biological process and has also been proposed for applications in photonics. This work reports on the excited state absorption spectrum of chlorophyll a solution from 460 to 700 nm, obtained through the white-light continuum Z-scan technique. Saturation of absorption was observed due to the ground state depletion, induced by the white-light continuum region that is resonant with the Q band of chlorophyll a. The authors also observed reverse saturation of absorption related to the excitation from the first excited state to a higher energy level for wavelengths below 640 nm. An energy-level diagram, based on the electronic states of chlorophyll a, was employed to interpret their results, revealing that more states than the ones related to the Q and B bands participate in the excited state absorption of this molecule. [ABSTRACT FROM AUTHOR]

Numerous single pulse and pulse train Z-scan techniques are employed to explain the resonant nonlinear absorption dynamics of zinc (Zn)-phthalocyanines in dimethyl sulfoxide (DMSO). The excited singlet state absorption cross-section determined is shown to be higher than the ground state one.

A Z-scan technique at 532 nm with different pulses of a Q-switched and model locked laser was used to explore the excited state dynamics of [Zn.sup.2+], [Fe.sup.3+], and [Mn.sup.3+] meso-tetra(sulfonatophenyl) porphyrin complexes. The data obtained for ground state cross-sections provide insight into the singlet and triplet excited state cross-sections, fluorescence, inter-system crossing, and internal conversion quantum yield and characteristic times.

The effect of temperature on the two-photon absorption cross section of azoaromatic chromophores is reported.