In-flow Optical Characterization of Flame-Generated Carbon Nanoparticles Sampled from a Premixed Flame

In this work, the optical absorption properties of carbon nanoparticles are investigated by applying in-flow extinction and laser-induced incandescence measurements. Carbon nanoparticles are produced in an ethylene/air premixed flame and sampled at different heights above the burner. From extinction measurements, the absorption coefficient is obtained in a wide spectral range, considering the scattering negligible in our experimental conditions. With the application of the Tauc plot the optical band gap is evaluated at the sampling heights under analysis. The increase of this value with the decrease in the height is consistent with quantum confinement effect detected in the inception region of the flame. Two-color laser induced incandescence measurements are performed at a relatively high laser fluence. The fluence curves, given by the particle temperature under laser irradiation versus laser fluence, are also obtained. A significant difference in the optical properties of these particles is observed changing the sampling height. Moreover considering the fluence curve in the low laser fluence regime, the refractive index absorption function E(m) is evaluated at the 1064 nm excitation wavelength. Finally, the knowledge of the behavior of the absorption coefficient in a wide spectral range allows retrieving the values and the behavior of E(m) as a function of wavelength.