Reflection of nanosecond Nd:YAG laser pulses in ablation of metals

Abstract

Hemispherical total reflectivity of copper, nickel, and tungsten in ablation by nanosecond Nd:YAG laser pulses in air of atmospheric pressure is experimentally studied as a function of laser fluence in the range of 0.1-100 J/cm(2). Our experiment shows that at laser fluences below the plasma formation threshold the reflectivity of mechanically polished metals remains virtually equal to the table room-temperature reflectivity values. The hemispherical total reflectivity of the studied metals begins to drop at a laser fluence of the plasma formation threshold. With increasing laser fluence above the plasma formation threshold the reflectivity sharply decreases to a low value and then remains unchanged with further increasing laser fluence. Computation of the surface temperature at the plasma formation threshold fluence reveals that its value is substantially below the melting point that indicates an important role of the surface nanostructural defects in the plasma formation on a real sample due to their enhanced heating caused by both plasmonic absorption and plasmonic nanofocusing.

Laser ablation of a Cu–Al–Ni combinatorial thin film library: analysis of crater morphology and geometry

“…4); the area richest in Al has the lowest reflectivity (R * 30%) and will thus absorb a higher amount of the incoming laser radiation compared to the area with least Al (R * 70%). These values are found to be generally lower than the overall values for reflectivity of the three metals at 1064 nm (Cu * 90%, Al * 80% and Ni * 70% of the incident radiation [15]). The optical properties of a material are not determined solely by chemical composition; therefore, surface microstructure The results show that, besides the compositional gradient across the surface, the CuAlNi thin film exhibits a morphological gradient as well.…”

“…In other words, when irradiating a metal with ns IR laser pulses in atmospheric conditions, plasma formation threshold was reported to be just 0.1-0.2 J/cm 2 higher than the ablation threshold [15,19]. Thus, with the lower ablation threshold, as the laser reached the workpiece more material was vaporised, leading to the formation of a dense cloud in front of the target.…”

Nevada National Security Site Site-Directed Research and Development FY 2014 Annual Report

“…We assumed a large uncertainty of 50% in our measurements of fluence with this method. The amount of laser fluence used in these measurements is roughly a factor of ten below the threshold of plasma formation and damage for typical metal surfaces (Benavides 2011), and we did not observe any laser-induced damage to the Cr-coated tin samples during preshot testing with laser pulses.…”

Self‐Folding Metal Origami

“…This reflectivity can vary significantly for different metals at the same wavelength. For instance, with an Nd:YAG laser, one of the most common laser types for metal ablation, the reflectivity at lower laser powers is 0.9, 0.72, and 0.6 for copper, nickel, and tungsten respectively . A copper sheet therefore requires four times as much power to fold at that wavelength than a tungsten one.…”