We present a novel optical aerosol particle detector based on Xe flash lamp excitation and spectrally resolved fluorescence acquisition. We demonstrate its performances on three natural pollens acquiring in real-time scattering intensity at two wavelengths, sub-microsecond time-resolved scattering traces of the particles’ passage in the focus, and UV-excited fluorescence spectra. We show that the device gives access to a rather specific detection of the bioaerosol particles.
Abstract:We present a technique to characterize ultrashort pulses at the focal plane of a high numerical aperture objective with unprecedented spatial resolution, by performing a FROG measurement with a single nanocrystal as nonlinear medium. This approach can be extended to develop novel phase-sensitive techniques in laser scanning microscopy, probing the microscopic environment by monitoring phase and amplitude distortions of femtosecond laser pulses.
Femtosecond laser induced multi-photon excited fluorescence (MPEF) from individual airborne particles is tested for the first time for discriminating bioaerosols. The fluorescence spectra, analysed in 32 channels, exhibit a composite character originating from simultaneous two-photon and three-photon excitation at 790 nm. Simulants of bacteria aggregates (clusters of dyed polystyrene microspheres) and different pollen particles (Ragweed, Pecan, Mulberry) are clearly discriminated by their MPEF spectra. This demonstration experiment opens the way to more sophisticated spectroscopic schemes like pump-probe and coherent control. Fundamental developments and applications in reacting flows," Prog. Energ. Combust. 36, 280-306 (2010).
We measured the electric charge release from single watermicrodroplets illuminated by ultrashort laser filaments in air. This charge is up to 600 times larger than from a comparable filament volume in air. In contrast, for atmospheric droplet concentrations and sizes, the volume-averaged overall droplet contribution to the charge is small as compared with that of the filaments along its whole propagation path
The influence of aerosols on climate is highly dependent on the particle size distribution, concentration, and composition. In particular, the latter influences their ability to act as cloud condensation nuclei, whereby they impact cloud coverage and precipitation. Here, we simultaneously measured the concentration of aerosols from sea spray over the North Atlantic on board the exhaust-free solar-powered vessel “PlanetSolar”, and the sea surface physico-chemical parameters. We identified organic-bearing particles based on individual particle fluorescence spectra. Organic-bearing aerosols display specific spatio-temporal distributions as compared to total aerosols. We propose an empirical parameterization of the organic-bearing particle concentration, with a dependence on water salinity and sea-surface temperature only. We also show that a very rich mixture of organic aerosols is emitted from the sea surface. Such data will certainly contribute to providing further insight into the influence of aerosols on cloud formation, and be used as input for the improved modeling of aerosols and their role in global climate processes.
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