Impacts of Ambient and Ablation Plasmas on Short- and Ultrashort-Pulse Laser Processing of Surfaces

Abstract

Abstract:In spite of the fact that more than five decades have passed since the invention of laser, some topics of laser-matter interaction still remain incompletely studied. One of such topics is plasma impact on the overall phenomenon of the interaction and its particular OPEN ACCESSMicromachines 2014, 5 1345 features, including influence of the laser-excited plasma re-radiation, back flux of energetic plasma species, and massive material redeposition, on the surface quality and processing efficiency. In this paper, we analyze different plasma aspects, which go beyond a simple consideration of the well-known effect of plasma shielding of laser radiation. The following effects are considered: ambient gas ionization above the target on material processing with formation of a "plasma pipe"; back heating of the target by both laser-driven ambient and ablation plasmas through conductive and radiative heat transfer; plasma chemical effects on surface processing including microstructure growth on liquid metals; complicated dynamics of the ablation plasma flow interacting with an ambient gas that can result in substantial redeposition of material around the ablation spot. Together with a review summarizing our main to-date achievements and outlining research directions, we present new results underlining importance of laser plasma dynamics and photoionization of the gas environment upon laser processing of materials.

Ultrashort pulse laser ablation of dielectrics: Thresholds, mechanisms, role of breakdown

“…With almost twice increased fluence, the depth of the crater is increasing only slightly (Fig. 3, 59 and 112 J/cm 2 ) that can be attributed to enhanced light absorption during beam propagation through air at larger fluences due to multiphoton/tunneling ionization24. At fluences ≥100 J/cm 2 a third, outer rim is formed with the diameter more than 3 times exceeding the beam diameter (1/e 2 ).…”

“…3, 112 J/cm 2 ). Most plausibly, this can be attributed to air ionization effects2425. Upon propagation toward the sample surface, a high-intensity laser beam induces ionization of air molecules that is more efficient in the higher intensity regions of the beam cross section.…”

“…Upon propagation toward the sample surface, a high-intensity laser beam induces ionization of air molecules that is more efficient in the higher intensity regions of the beam cross section. Before reaching the sample surface, the laser beam can be essentially flattened due to air ionization24. Thus, air ionization can lead to beam “self-healing” via smoothing high-intensity imperfectnesses.…”

“…The incident laser energy is too low at the positions between primary and outer rims and, thus, cannot induce material damage. Several mechanisms can contribute to such “matryoshka-like” crater formation with material damage beyond the irradiation spot: (a) air and ablation plasma reemission during recombination of plasmas24 (note that air plasma recombines within several nanoseconds after femtosecond laser pulses26 while ablation products can produce light emission at a longer timescale upon plume expansion27); (b) strong scattering of the tail part of the beam by air plasma produced by the beam front28; (c) a strong shock wave generated upon air plasma recombination which travels outward the plasma region and can induce material modification at its contact with the surface324. It should be mentioned that, for our τ L at fluences above ~80 J/cm 2 , the beam propagation is affected by the Kerr nonlinearity that provides more effective air ionization before the geometrical focus and, thus, higher scattering of laser light.…”

High-Speed Visualization of Nanopowder Combustion in Air

“…Nowadays, a number of methods are used for producing new materials, which are associated with the interaction of powerful energy fluxes with a matter or high-temperature combustion processes [1][2][3][4][5][6][7][8][9]. One of these processes is manufacturing aluminum nitride (AlN) by combustion of aluminum nanopowder in air [1][2][3][4][5][6][7].…”