Particle size distributions of aerosols formed by laser ablation of solids at 760 Torr
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The size distributions of aerosol particles generated in N 2 and O 2 at ambient atmospheric pressure by repetitive excimer laser ablation of solids have been measured in quasi-steady-state from 10 nm to 1 /xm diameter with a differential mobility analyzer (DMA). A light scattering technique extended the range of measurable sizes up to 20 /xm, beyond the upper limit of sizes observed in the aerosol. Irradiation near focus was required to observe metal particles above 0.1 ^ m diameter. YBCO ceramic (YBa 2 Cu 3 0 7 ) produced copious smaller particles with mild focusing. For an ablated polymer, PMMA, particulate production increased and the size distribution altered shape with continued energy deposition.
I. INTRODUCTION The interactions of particles and high power lasers have been extensively researched in programs concerned with beam propagation,1 thermonuclear fusion,2 and materials processing.3-4 At lower irradiances (>0.04 W/cm 2 ), photodesorption has reportedly modified the size distribution of pre-existing metal particles on a surface.56 Lasers have been used to characterize particles by their luminosity or other spectral signatures,1'7 but the scattering response has proven more generally useful for size determination, following Mie's solution of Maxwell's equations for a plane electromagnetic wave interacting with a homogeneous spherical particle.8 Intensity limits the minimum attainable with commercial instrumentation to slightly < 1 /xm, although the method has reportedly been applied down to 0.01 /xm diameter,9 about where the particle may no longer be assumed to be homogeneous.6 Early work on particle generation by lasers was restricted to ions and neutrals of, at most, several atoms.10 It has long been hoped that rapid laser processing would lead to particulates with novel properties.9 Matsunawa and Katayama have produced ultrafine particles by laser ablation, and have examined their morphology and crystal structure.11 They and others have taken size distributions of deposited particles by electron microscopy.12 High temperature superconductor films, deposited by laser ablation, contain particulates.13 Vaporization, condensation, fracture, and fluid processes have been proposed as mechanisms by which particulates are produced by laser ablation. II. EXPERIMENTAL PROCEDURE We report real time measurements of size distributions of aerosol particles 10 nm to
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