Interaction of wide band gap single crystals with 248 nm excimer laser irradiation. VII. Localized plasma formation on NaCl single crystal surfaces

Abstract

Wide band gap insulators containing defects exposed to nanosecond pulses of UV laser radiation at fluences close to the damage threshold often display highly localized flashes of light. In this work, we show that flashes observed during irradiation of cleaved, single crystal NaCl at relatively low fluences are due to localized plume fluorescence. By comparing time-resolved optical images of this fluorescence with subsequent scanning electron microscope images of surface topography, we show that these flashes are often associated with micron-dimension surface and near-surface damage, typically associated with cleavage steps. With continued laser irradiation, plume fluorescence at previously damaged regions usually grows stronger from pulse to pulse. In some cases, weak plume fluorescence disappears after one laser pulse, and may or may not reappear with continued irradiation. We interpret these results in terms of localized laser absorption by deformation-induced defects generated during cleavage. Deliberately deformed material, produced by indentation, is damaged at considerably lower laser fluences, consistent with this interpretation. We suggest that mobile excitations produced by laser absorption preferentially decay along dislocation cores, which strongly localizes laser-induced thermal stresses and damage.

Role of marble microstructure in near-infrared laser-induced damage during laser cleaning

“…58 Adsorbed ions or neutrals, which compensate the charge-defect induced by a vacancy, are released following defect-mediated laser energy absorption, which leads to thermal emission of these particles as visible luminescing plasma plumes. 29 Our results showed that laser irradiation reduced calcite defect density, presumably due to point and line defects annealing, 59 as inferred from the sharpening of the Bragg peak profile and the increase of D 104 values. The local ⌬T following laser irradiation ͑see previous section͒ can be accounted for by this annealing effect.…”

The onset of optical breakdown in KrF-laser-irradiated silica glass surfaces

“…By the fourth pulse, the localized luminescence disappears, leaving only the bulk red luminescence. The appearance and disappearance of localized luminescence was also observed in NaCl [12,13]. We attribute this localized luminescence to micro-plasmas formed when near-surface defective regions are strongly excited by the laser.…”

“…Time-resolved luminescence spectra were acquired with a gated optical multichannel analyzer (OMA) in conjunction with a grating spectrometer (JASCO CT-25C, 150 lines/mm), and luminescence images were obtained using a gated ICCD camera. The details of the experimental have been described previously [11][12][13]. Up to 10 luminescence images were acquired for each laser pulse at a fixed fluence; then the fluence was raised and the same procedure repeated until optical breakdown was observed.…”

<title>F<formula><inf><roman>2</roman></inf></formula>-laser-induced damage on transparent fluoride crystals</title>

“…6 shows SEM images of the F2-laser-damaged region on both surfaces of LiCaA1F6. In BaF2, the damaged surface is full of cracks along the crystallographic axes, and the corners of the cracks are round by melting, similar to that of severely damaged NaCI under KrF laser irradiation [33]. The degree of melting differed from sample to sample.…”