On the influence of surface condition on air plasma formation near metals irradiated by microsecond TEA CO<sub>2</sub>laser pulses

Ursu, I.; Apostol, I.; Crǎciun, D.; Dinescu, M.; Mihăilescu, I. N.; Nistor, L. C.; Popa, Al.; Teodorescu, V. S.; Prokhorov, A M; Chapliev, N. I.; Konov, V. I.

doi:10.1088/0022-3727/17/4/010

Cited by 29 publications

(6 citation statements)

References 7 publications

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“…The probes were further polished and then cleaned in a ultrasonic ethanol bath. Second, the decrease also continues above the melting point, which contradicts the observations for aluminum [21,22,23]. Therefore, we believe that the measured drop in energy coupling is caused by the temperature increase only.…”

Section: Resultscontrasting

confidence: 61%

“…Some studies reported higher values of energy coupling on oxidized surfaces [18,19,20]. Contradictorily, others observed an initial decrease of the coupling efficiency while the effect of oxidation, in turn resulting in higher coupling efficiencies, only takes place above a certain temperature range [21,22,23]. The decreasing coupling efficiency was ruled as due to a cleaning effect of the surface due to the laser irradiation.…”

Section: Introductionmentioning

confidence: 99%

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Energy Coupling of Laser Radiation on AISI 304 Stainless Steel: Effect of High Temperatures and Surface Oxidation

2019

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The industrial application of laser materials processing methods is still far ahead of research into the physical phenomena occurring during these processes. In particular, the effect of high temperatures on the energy coupling of laser irradiation of metals is poorly understood. However, most processes in laser materials treatment involve temperatures above the melting point or even cause evaporation. This study therefore evaluates the effect of high temperatures on the energy coupling efficiency of stainless steel experimentally for three typical laser wavelengths (515 nm, 1.07 µm, 10.6 µm). As a result, it is shown that the effect of temperature on the energy coupling efficiency depends on the wavelength. In this context the relevance of the X-point phenomenon known from the emissivity theory could be demonstrated for laser material processing. Further, the effect of a process-induced surface oxidation is analyzed. At temperatures above 650 °C the energy coupling efficiency dramatically increases to around 65% at melting point and stays at this high level even in the liquid phase.

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Section: Resultscontrasting

confidence: 61%

Section: Introductionmentioning

confidence: 99%

Energy Coupling of Laser Radiation on AISI 304 Stainless Steel: Effect of High Temperatures and Surface Oxidation

2019

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“…59 Additionally, Ursu et al, used electron microscopy to analyze the change in the breakdown threshold after applying laser irradiation to a metallic surface and determined that defects produced by the irradiation lowered vaporization threshold, which could lower the breakdown voltage of a nearby gas. 60 A study assessing the impact of surface polishing on flashover properties in alumina ceramics demonstrated that surface breakdown depended on the abrasiveness of the polishing material and direction of polishing sequence (coarse to fine or fine to coarse). 61 While these studies provide valuable information about how surface properties can impact the breakdown voltage, a comprehensive study directly quantifying these relationships (e.g., how a discharge changes work function and how different sizes and shapes of surface features effect breakdown) is still needed to eliminate the need for a fitting parameter in the present model.…”

Section: Discussionmentioning

confidence: 99%

A universal theory for gas breakdown from microscale to the classical Paschen law

Loveless

Garner

2017

Physics of Plasmas

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While well established for larger gaps, Paschen's law (PL) fails to accurately predict breakdown for microscale gaps, where field emission becomes important. This deviation from PL is characterized by the absence of a minimum breakdown voltage as a function of the product of pressure and gap distance, which has been demonstrated analytically for microscale and smaller gaps with no secondary emission at atmospheric pressure [A. M. Loveless and A. L. Garner, IEEE Trans. Plasma Sci. 45, 574-583 (2017)]. We extend these previous results by deriving analytic expressions that incorporate the nonzero secondary emission coefficient, c SE , that are valid for gap distances larger than those at which quantum effects become important ($100 nm) while remaining below those at which streamers arise. We demonstrate the validity of this model by benchmarking to particle-in-cell simulations with c SE ¼ 0 and comparing numerical results to an experiment with argon, while additionally predicting a minimum voltage that was masked by fixing the gap pressure in previous analyses. Incorporating c SE demonstrates the smooth transition from field emission dominated breakdown to the classical PL once the combination of electric field, pressure, and gap distance satisfies the conventional criterion for the Townsend avalanche; however, such a condition generally requires supra-atmospheric pressures for breakdown at the microscale. Therefore, this study provides a single universal breakdown theory for any gas at any pressure dominated by field emission or Townsend avalanche to guide engineers in avoiding breakdown when designing microscale and larger devices, or inducing breakdown for generating microplasmas.

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“…Bloembergen [42], Apostol et al [43], and other authors [34,35,44] explained the breakdown phenomenon for I las << I vap by the presence of surface defects. They can be vaporized easier than a solid with a perfect flat and defect-free surface.…”

Section: The Role Of Surface Defectsmentioning

confidence: 94%

Laser–Plasma Interactions

Mihăilescu

Hermann²

2010

Laser Processing of Materials

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The purpose of the present chapter is to give an introduction into the physics of laser plasma interactions that govern the coupling of laser energy into the matter. Processes induced by laser pulses of nano-and femtosecond durations are discussed in the framework of different applications. In particular, the roles of non-linear absorption and avalanche ionization in plasma heating are discussed and a critical review of related experimental and theoretical studies is given. 4 Laser-Plasma Interactions 51 electrons, is related to the number of electrons inside the Debye sphere having a volume V D D 4 3 D 3 . 1 We have

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On the influence of surface condition on air plasma formation near metals irradiated by microsecond TEA CO₂laser pulses

Cited by 29 publications

References 7 publications

Energy Coupling of Laser Radiation on AISI 304 Stainless Steel: Effect of High Temperatures and Surface Oxidation

Energy Coupling of Laser Radiation on AISI 304 Stainless Steel: Effect of High Temperatures and Surface Oxidation

A universal theory for gas breakdown from microscale to the classical Paschen law

Laser–Plasma Interactions

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On the influence of surface condition on air plasma formation near metals irradiated by microsecond TEA CO2laser pulses

Cited by 29 publications

References 7 publications

Energy Coupling of Laser Radiation on AISI 304 Stainless Steel: Effect of High Temperatures and Surface Oxidation

Energy Coupling of Laser Radiation on AISI 304 Stainless Steel: Effect of High Temperatures and Surface Oxidation

A universal theory for gas breakdown from microscale to the classical Paschen law

Laser–Plasma Interactions

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Product

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On the influence of surface condition on air plasma formation near metals irradiated by microsecond TEA CO₂laser pulses