Two-color laser induced evaporation dynamics of liquid aerosols probed by time-of-flight mass spectrometry

The first results are reported from an investigation into the evaporation dynamics of liquid aerosols using a newly constructed two color laser time-of-flight mass spectrometer, which utilizes a CO2 laser (IR) for vaporization and an excimer laser (UV) for ionization. The results indicate that the CO2 laser with an intensity greater than 1.2 X 10(8) W/cm(2) completely vaporizes the aerosol particle and that this preevaporation of the liquid aniline particle increases the ion signal by as much as two orders of magnitude compared to direct ionization of the particle,vith the excimer laser only. The present focus is on exploring the vaporization process by varying both the timing between the two lasers and the CO2 laser fluence. A three-dimensional (3D) model of the laser-induced gas plume is used to extract the associated velocity distribution and its temperature of 1300 and 2500 K for CO2 laser intensities of 1.2 x 10(8) W/cm(2) and 2.8 X 10(8) W/cm(2), respectively. At the higher CO2 laser energies, the data could only be fitted by the addition of a 350 m/s stream, or entrainment, velocity to the three-dimensional Maxwell-Boltzmann distribution, consistent with hydrodynamic expansion.