Pulsed laser-induced melting of precision diamond- machined Cu, Ag, and Au at infrared wavelengths

Threshold for characteristics of pulsed laser-induced damage have been measured on precision diamond-machined Cu, Ag, and Au surfaces at 10.6, 3.8, 2.7, and 1.06 μm wavelengths. Pulse lengths range from 2 μs to 9 ns, and focal spot diameters range from 238 to 52 μm. Comparison is made with melt thresholds calculated from one-dimensional heat flow considerations with a spot-size correction. The calculation incorporates waveform shape, as well as temperature-dependent absorption and thermal properties. Agreement is excellent for Ag, except at 1.06 μm, while agreement for Cu and Au is good only at 10.6 μm. Results suggest that disturbance of crystalline surface order has an important influence, especially at wavelengths shorter than 10.6 μm. A singular departure from calculated Cu and Au thresholds at 3.8 μm, using a multipeaked waveform, may have important implications for repetitively pulsed applications. For Cu at 10.6 μm, damage scales with pulse length according to the
\sqrt{\tau}
law provided the pulse length as appropriately defined.