Laser comminution of submerged samples

Abstract

With the long-term goal in mind of investigating possible designs for a “universal, solid-sample comminution technique” for elemental analysis of debris and rubble, we have studied pulsed-laser ablation of solid samples that were submerged in water. Using 351-nm, 15-ns laser pulses with energy between 1 J and 0.35 J, intensities between 500 MW/cm2 and 30 MW/cm2, and samples of broken rock [quartzite] and concrete debris, we have observed conditions in which the laser-driven process can remove material from the solid target substrate, dissolving it and/or converting it into ultrafine particles in a controlled manner. Our study used impure, non-metallic substrates and investigated both the rate of material removal as well as the size distribution of particles that were ablated from the process. We studied ablation at lower regimes of intensity and fluence [below 100 MW/cm2 and 0.4 J/cm2, respectively] than has previously attracted attention and discovered that there appears to be a new regime for energy-efficient material removal [Q* < 4000 J/g, for quartzite and <2000 J/g for concrete] and for the generation of ultrafine particles.

Laser-driven hydrothermal processing: a new, efficient technique to effect separation of silica from other oxides for analysis

“…In our first report, we observed efficient removal of material (<4 kJ g −1 for quartzite and <2 kJ g −1 for cement in concrete) and ⩽100 μm colorless particles lining the crater that formed, after directing 15 ns, 351 nm laser pulses with 7 and 3.5 J cm −2 (Intensity ~470 and 230 MW cm −2 ) onto watersubmerged quartzite [1]. The intensity we used was too low either to strike a plasma [2] or to effect thermal vaporization [1].…”

“…In our first report, we observed efficient removal of material (<4 kJ g −1 for quartzite and <2 kJ g −1 for cement in concrete) and ⩽100 μm colorless particles lining the crater that formed, after directing 15 ns, 351 nm laser pulses with 7 and 3.5 J cm −2 (Intensity ~470 and 230 MW cm −2 ) onto watersubmerged quartzite [1]. The intensity we used was too low either to strike a plasma [2] or to effect thermal vaporization [1]. When examined with an optical microscope, the colorless particles' appearance was consistent with a transient dissolution and recrystallization process, due to the pressure and temperature pulse caused by the laser absorption and thermally-driven expansion of the material [3].…”

Fabrication of surrogate glasses with tektite composition

“…Whatever the source maybe, elements of interest must be separated in a way that contaminates are not introduced in the processing of specimens. In addition, because sample sizes are often small, processing of samples should involve as little loss of material as possible [2,6]. These two restrictions, separation of components and small amounts of material available, place limits on the typical separation techniques employed, e.g.…”

“…mechanical comminution or chemical separation by dissolution with a concentrated acid. To solve these problems, a new technique for collecting specimens was developed involving the rapid communications of samples termed laser-driven hydrothermal processing (LDHP) [6,7].…”

“…Initial testing of LDHP was performed on quartzite [6] and concrete [8] by Mariella et al Further studies conducted at the Naval Postgraduate School by Menon et al, was performed on naturally occurring minerals, tektite and obsidian [9,10]. The aim of the later work was to characterize LDHP processed material like trinitite, a glass which was formed during the first atomic bomb test.…”