The properties of excitons in one-dimensional molecular aggregates, dissolved at room temperature in a liquid, were studied by means of femtosecond nonlinear optical experiments. Both the one-exciton band ͑i.e., Frenkel-excitons͒ and multiexciton bands contribute to the observed nonlinear optical response. The rapid motions in the liquid lead to ultrafast perturbations of the molecular energy levels. This localizes the excitons on limited sections of the chains of aggregated molecules. Ultrafast frequency-resolved pump-probe spectroscopy on the lowest two exciton bands was employed to determine the delocalization length of the optical excitations. The kinetics of the exciton populations was measured by ultrafast grating scattering experiments and time-resolved single photon counting. A model is described in which the multiexciton bands act as doorway states in the exciton-exciton annihilation process. These bands thereby determine the population decay of the Frenkel excitons at high excitation densities. Room temperature photon echo experiments show that stochastic perturbations of the exciton transition frequencies occur on two distinct time scales. In particular the slow components of the fluctuations are affected by motional narrowing, associated with the exciton delocalization length. It is therefore argued that the optical dephasing of excitons is directly related to the spatial extent of the excitation on the aggregate chain.

Isotope analysis of water by means of near-infrared dual-wavelength diode laser spectroscopy Gianfrani, L.; Gagliardi, G.; Burgel, M. van; Kerstel, E.R.Th.; Gianfrani, I.; Galgiardi, G. Link to publication in University of Groningen/UMCG research database Citation for published version (APA): Gianfrani, L., Gagliardi, G., Burgel, M. V., Kerstel, E. R. T., Gianfrani, I., & Galgiardi, G. (2003). Isotope analysis of water by means of near-infrared dual-wavelength diode laser spectroscopy. Optics Express, 11(13), 1566-1576. DOI: 10.1364/OE.11.001566 Copyright Other than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. Abstract: A novel diode laser spectrometer was developed using dualwavelength multiplexing, ensuring ideal conditions for high-precision and simultaneous measurements of the 2 H/ 1 H,

No abstract

No abstract

Carbon isotope ratio analysis using a laser-based technique has been performed in the field, on the gaseous emissions from an active volcano. We here describe that 13CO2/12CO2 determinations can be carried out in a quasi-continuous regime using a compact, selective and sensitive diode laser spectrometer at a wavelength of 2 mum. Within the Solfatara crater (near Naples, Italy), in a very harsh environment, we were able to determine relative 13CO2/12CO2 values, on the highest flux fumarole, with an accuracy of 0.5 per thousand. Regular and frequent observations of the carbon isotopes in volcanic gases, which become possible with our methodology, are of the utmost importance for geochemical surveillance of volcanoes.