A team of scientists from Università di Napoli and from Istituto di Ricerche sulla Combustione, both in Italy, and from Lund University in Sweden has directly measured combustion-generated nanometer-size organic carbon particles within a propane flame. Time-resolved fluorescence polarization anisotropy with 8-ps resolution proved that the flame produces particles about 3 nm in diameter. This is an important step for studying the particles’ environmental and biochemical behaviour.

The investigators’ calculations show that the anisotropy of fluorescence excited in the nanoparticle by an ultrashort laser pulse would fall because of buffeting by air molecules, with a decay time on the order 100 ps. To achieve the necessary time resolution, they produced 100-fs pulses with a Spectra-Physics Ti:sapphire laser and an Nd:YVO pump, and they synchronized a Hamamatsu streak camera with the 82-MHz pulse train. They also measured the flame’s background spectrum with a Jobin-Yvon spectrograph and subtracted it from the spectrum taken with the laser pulse to isolate the laser-induced fluorescence.

This direct approach avoids altering the combustion process or the particles themselves through the use of collection probes or solvents, respectively.

(Optics Express, 14 April 2008, pp. 5623-5632)