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Pulsed laser ablation (266nm) was used to generate metal particles of Zn and Al alloys using femtosecond (150 fs) and nanosecond (4 ns) laser pulses with identical fluences of 50 J cm -2 . Characterization of particles and correlation with InductivelyCoupled Plasma Mass Spectrometer (ICP-MS) performance was investigated. Particles produced by nanosecond laser ablation were mainly primary particles with irregular shape and hard agglomerates (without internal voids). Particles produced by femtosecond laser ablation consisted of spherical primary particles and soft agglomerates formed from numerous small particles. Examination of the craters by white light interferometric microscopy showed that there is a rim of material surrounding the craters formed after nanosecond laser ablation. The determination of the crater volume by white light interferometric microscopy, considering the rim of material surrounding ablation craters, revealed that the volume ratio (fs/ns) of the craters on the selected samples was approximately 9 (Zn), 7 (NIST627 alloy) and 5 (NIST1711 alloy) times more ablated mass with femtosecond pulsed ablation compared to nanosecond pulsed ablation. In addition, an increase of Al concentration from 0 to 5% in Zn base alloys caused a large increase in the diameter of the particles, up to 65% while using nanosecond laser pulses.When the ablated particles were carried in argon into an ICP-MS, the Zn and Al signals intensities were greater by factors of ~ 50 and ~ 12 for fs vs. ns ablation. Femtosecond 2 pulsed ablation also reduced temporal fluctuations in the 66 Zn transient signal by a factor of ten compared to nanosecond laser pulses.

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Laser ablation has proven to be an effective method for generating nanoparticles; particles are produced in the laser induced vapor plume during the cooling stage. To understand the in-situ condensation process, a series of time resolved light scattering images were recorded and analyzed. Significant changes in the condensation rate and the shape of the condensed aerosol plume were observed in two background gases, helium and argon. The primary particle shape and size distribution were measured using a transmission electron microscope (TEM), a scanning electron microscope (SEM) and a differential mobility analyzer (DMA). The gas dynamics simulation included nucleation and coagulation within the vapor plume, heat and mass transfer from the vapor plume to the background gas, and heat transfer to the sample. The experimental data and the calculated evolution of the shape of the vapor plume showed the same trend for the spatial distribution of the condensed particles in both background gases. The simulated 1 particle size distribution also qualitatively agreed with the experimental data. It was determined that the laser energy, the physical properties of the background gas (conductivity, diffusivity and viscosity), and the shape of the ablation system (ablation chamber and the layout of the sample) have strong effects on the condensation process and the subsequent sizes, shapes and degree of aggregation of the particles.--

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A study was made of the cooling of the laser induced vapor plume in background air.The temperature and size variations of the vapor plume were determined from spectroscopic measurements during the first few tens of micro-seconds after the laser pulse. Experiments were carried out over a range of laser spot sizes and energies ------------------------------------------------------------------------------------------- Keywords Laser ablation, plasma cooling, thermal radiation decrease of the vapor plume was independent of the plume size, shape, and position. For 1 larger optical thicknesses of the vapor plume, the calculations showed that the reflectivity of the sample surface and the size of the vapor plume would dramatically affect cooling of the vapor plume.2