Characterization of aerosol plumes in nanosecond laser ablation of molecular solids at atmospheric pressure

Abstract

Ablation of molecular solids with pulsed ultraviolet lasers at atmospheric pressure is an important process in (bio-)organic mass spectrometry. Of practical importance for analytical sampling and analysis are the plume formation and expansion. Plumes formed by atmospheric-pressure laser ablation of anthracene and 2,5-dihydroxybenzoic acid (2,5-DHB) were studied by light scattering imaging, which showed significant material release in the form of aerosols. The monitored plume expansion dynamics could be fitted to the drag-force model, yielding initial plume velocities of 150 m/s for anthracene and 43 m/s for DHB. While the angle of incidence does not affect the plume direction and propagation, a large dependence of the plume-expansion velocity on the laser pulse energy could be found, which is limited at atmospheric pressure by the onset of plasma shielding. With respect to analytical applications, the efficiency of sampling of the laser ablation products by a capillary could be experimentally visualized.

Nanosecond laser-induced shock propagation in and above organic liquid and solid targets

“…This is similar, but somewhat different, to the behavior observed in Ref. [22], where a steep rise in the ellipticity of the shockwave was followed by a decrease towards a more hemispherical shape. Given the uncertainty in the position due to the challenge in determining the precise shape of the front, all further measurements of the shockwave position will be relative to the horizontal axis.…”

“…Representative images for shockwaves in air above acetone are shown in Figure 2a-d. These images have much in common with previous reports of ns ablation of liquids [19][20][21] and organic matrices [22]. There is a welldefined shock wave and a clearly visible Mach stem at the base, see and the toroidal vapor cloud is eventually overtaken by strong recoil-induced ejection that closely resembles droplet dynamics at later times.…”

“…see Ref. [22], and references therein). In Figure 4, we display the position of the shock front as a function of time for vertical (R z ) and horizontal (R x ), respectively.…”

“…One aspect of plume expansion that does not appear to have been explicitly considered in recent work [22] is the influence of photolysis and pyrolysis of the target materials. The fragmentation of organic compounds into products that have a larger molar volume than the parent molecules could certainly play a role in this asymmetry and velocity of the shockwave.…”

A study of particulate matter concentration released during laser paint removal process on car coated substrate

“…The productions of PM was effected the average coating removal efficiency (ϵ) if the particles released redeposited on the crater surface [16,21]. However, the plume produced during laser irradiation on painted material is considered as the main factors to effect the process efficiency [18,19,22]. This is because some of the laser fluence energy was absorbed by the particle released in air, hence reduced the laser intensity to the next layers of the painted material [21].…”