Effect of tribological wear on ultraviolet laser interactions with single crystal NaNO3 and CaCO3

Abstract

We report measurements of the neutral and ion emissions accompanying laser irradiation of cleaved and abraded NaNO3 and CaCO3. In both materials, abraded surfaces yield especially intense positive ion emissions during laser irradiation at low fluences (i.e., fluences well below those required for surface damage and/or the formation of a fluorescent plume). Abraded NaNO3 also yields extremely intense neutral emissions (NO, O2) derived from NO3− decomposition. Measurements of neutral molecules released during abrasion show significant anion-derived emissions from both materials (CO2 from CaCO3; NO from NaNO3). We attribute the effect of abrasion on the laser-induced emissions to the production of easily photoionized electron traps during abrasion. Such traps are expected to strongly enhance photoinduced ion emission from both materials. Because the NO3− ion undergoes dissociative electron attachment, photoionizable defects also enhance NO emission during laser irradiation. In contrast, the CO32−anion does not appear to undergo dissociative electron attachment and no enhancement of CO2 emission is observed during laser irradiation.

<title>Charged-particle emission from dielectric materials initiated by a tunable picosecond mid-infrared laser</title>

“…High-energy positive ion emission from CaCO3 and NaNO3 has been reported during irradiation at 248 nm7 and 1 .064 im. 6 We have repeated the measurements at 248 nm in our current system and find good agreement with the reported energies. High-energy ion emission from NaNO3 in the ultraviolet and near-infrared has been attributed to an electrostatic ejection mechanism involving the photoionization of near surface anion vacancy sites.…”

“…Further, measurements made in our system using an excimer laser (MPB Technologies, Pointe Claire QC, Canada) operating at 248 nm to irradiate the sample agree with known Na energies from NaNO3 at 248 nm. 6 The drift distance was 28.5 cm. Negatively charged particles were detected with a chevron microchannel plate detector.…”

Laser desorption of energetic sodium ions from single-crystal NaNO3 at 1064 nm

“…Although the major absorption bands of NaNO 3 have been observed at ∼ 6.4 eV, ∼ 10.5 eV, and ∼ 12.1 eV [12], it has been shown in previous work that exposure of NaNO 3 surfaces to 248-nm (5-eV) excimer laser radiation results in both neutral and ion emission [2,7,13]. Furthermore, the important role of defects during the emission process has been demonstrated by comparing the emission from as-cleaved, abraded and electron irradiated surfaces.…”

“…However, reliable quantitative analysis requires an understanding of the photodecomposition and desorption mechanisms, since they can affect the sample composition and resulting signals. For this purpose a number of studies have been recently performed that used laser fluences well below the ablation threshold, so that changes in the surface composition and morphology, as well as the interactions among the emitted species can be kept to a minimum [2][3][4][5][6][7][8][9][10][11].Although the major absorption bands of NaNO 3 have been observed at ∼ 6.4 eV, ∼ 10.5 eV, and ∼ 12.1 eV [12], it has been shown in previous work that exposure of NaNO 3 surfaces to 248-nm (5-eV) excimer laser radiation results in both neutral and ion emission [2,7,13]. Furthermore, the important role of defects during the emission process has been demonstrated by comparing the emission from as-cleaved, abraded and electron irradiated surfaces.…”

“…However, reliable quantitative analysis requires an understanding of the photodecomposition and desorption mechanisms, since they can affect the sample composition and resulting signals. For this purpose a number of studies have been recently performed that used laser fluences well below the ablation threshold, so that changes in the surface composition and morphology, as well as the interactions among the emitted species can be kept to a minimum [2][3][4][5][6][7][8][9][10][11].…”