Interaction of wide band gap single crystals with 248 nm excimer laser radiation. V. The role of photoelectronic processes in the formation of a fluorescent plume from MgO

Ermer, David R.; Langford, S. C.; Dickinson, J. T.

doi:10.1063/1.364183

Cited by 41 publications

(12 citation statements)

References 19 publications

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“…Because both charge clouds and energetic metastable particles are difficult to perturb with electric fields, distinguishing them can be difficult in many cases. Charge clouds in particular are frequently observed from ionic materials [329][330][331], even at laser fluences insufficient to produce visible luminescence [229]. The difficulty in producing ion emission from most polymeric substances is consistent with the weakness of charge clouds observed in this work.…”

Section: Additional Experimentssupporting

confidence: 84%

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Laser Application of Polymers

Lippert

2004

Polymers and Light

150

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Laser ablation of polymers has been studied with designed materials to evaluate the mechanism of ablation and the role of photochemically active groups on the ablation process, and to test possible applications of laser ablation and designed polymers. The incorporation of photochemically active groups lowers the threshold of ablation and allows high-quality structuring without contamination and modification of the remaining surface. The decomposition of the active chromophore takes place during the excitation pulse of the laser and gaseous products are ejected with supersonic velocity. Time-of-flight mass spectrometry reveals that a metastable species is among the products, suggesting that excited electronic states are involved in the ablation process. Experiments with a reference material, i.e., polyimide, for which a photothermal ablation mechanism has been suggested, exhibited pronounced differences. These results strongly suggest that, in case of designed polymers which contain photochemically active groups, a photochemical part in the ablation mechanism cannot be neglected. Various potential applications for laser ablation and the special photopolymers were evaluated and it became clear that the potential of laser ablation and specially designed material is in the field of microstructuring. Laser ablation can be used to fabricate three-dimensional elements, e.g., microoptical elements.Keywords Laser ablation · Ablation mechanism · Photopolymers · Polyimide · Spectroscopy This was not always true, of course. For many years, the laser was viewed as "an answer in search of a question". That is, it was seen as an elegant device, but one with no real useful application outside of fundamental scientific research. In the last two to three decades however, numerous laser applications have moved from the laboratory to the industrial workplace or the commercial market. Lasers are unique energy sources characterized by their spectral purity, spatial and temporal coherence, and high average peak intensity. Each of these characteristics has led to applications that take advantage of these qualities: -Spatial coherence: e.g., remote sensing, range finding and many holographic techniques. -Spectral purity: e.g., atmospheric monitoring based on high-resolution spectroscopies. -and of course the many other applications in communication and storage, e.g., CDs.All of these high-tech applications have come to define everyday life in the late twentieth century. One property of lasers, however, that of high intensity, did not immediately lead to "delicate" applications but rather to those requiring "brute force". That is, the laser was used in applications for removing material or heating. The first realistic applications involved cutting, drilling, and welding, and the laser was little more advanced than a saw, a drill, or a torch. In a humorous vein A.L. Schawlow proposed and demonstrated the first "laser eraser" in 1965 [4], using the different absorptivities of paper and ink to remove the ink without damaging the und...

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Section: Additional Experimentssupporting

confidence: 84%

“…In previous work, signals have been frequently found that are not mass resolved and that can be attributed to nonequilibrium plasmas, which are also called €charge clouds [329][330][331]. The substantial electron component of these charge clouds can screen the accompanying ions from applied electric fields.…”

Section: Additional Experimentsmentioning

confidence: 99%

Laser Application of Polymers

Lippert

2004

Polymers and Light

150

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“…It behaves much like an expanding ball of low-density plasma moving away from the surface. 14,15 The dominant contribution to the negative charge in a nearly neutral Ϯ charge cloud is typically made by electrons. The large excess of positive ions ͑principally Si + ͒ over negative ions ͑principally O − ͒ inferred from the angular distribution measurements support the hypothesis that electrons greatly outnumber the negative ions.…”

Section: Total ؎ Charge Measurementsmentioning

confidence: 99%

Interaction of vacuum ultraviolet excimer laser radiation with fused silica. III. Negative ion formation

George

Langford

Dickinson

2010

Journal of Applied Physics

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We report mass- and time-resolved measurements of negative ions produced by exposing fused silica to 157 nm radiation at fluences below the threshold for optical breakdown. The principal observed negative ions are O−, Si−, and SiO−, in order of decreasing intensity. The peak in the negative ion time-of-flight signals occurs after the peak in the positive ion signal and before the peak in the corresponding neutral atom or molecule signal. The negative ion intensities are strong functions of the degree of overlap between the positive ion and neutral atom densities. We propose that O−, Si−, and SiO− are created after the laser pulse, by electron attachment to these neutral particles and that the electrons participating in attachment events are trapped in the electrostatic potential of the positive ions.

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“…In this respect, silica may be like single crystal MgO, where ion emission is observed at laser fluences well below those required for detectable neutral emission. 8 More sensitive searches for neutral species are in progress. Typical Si + and O + TOF signals are shown in Figures 1 and 2, respectively.…”

Section: Resultsmentioning

confidence: 99%

<title>The role of defects in the laser desorption of ions from fused silica at 157 nm</title>

et al. 2007

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At fluences well below the threshold for plasma formation, we have characterized the direct desorption of atomic ions from fused silica surfaces during 157-nm irradiation by time-resolved mass spectroscopy. The principal ions are Si + and O + . The emission intensities are dramatically increased by treatments that increase the density of surface defects. Molecular dynamics simulations of the silica surface suggest that silicon ions bound at surface oxygen vacancies (analogous to E' centers) provide suitable configurations for the emission of Si + . We propose that emission is best understood in terms of a hybrid mechanism involving both antibonding chemical forces (MenzelGomer-Redhead model) and repulsive electrostatic forces on the adsorbed ion after laser excitation of the underlying defect.

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Interaction of wide band gap single crystals with 248 nm excimer laser radiation. V. The role of photoelectronic processes in the formation of a fluorescent plume from MgO

Cited by 41 publications

References 19 publications

Laser Application of Polymers

Laser Application of Polymers

Interaction of vacuum ultraviolet excimer laser radiation with fused silica. III. Negative ion formation

<title>The role of defects in the laser desorption of ions from fused silica at 157 nm</title>

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