Laser ablation of metals and semiconductors with 100 ps to 100 μs pulses

摘要

Laser ablation of aluminum, silicon, titanium, germanium, and indium antimonide at 1064 nm in ambient laboratory air with pulse durations ranging from 100 ps to 100 μs has been characterized with optical microscopy. Highly focused spots of 10 μm yields fluences of 0.004 to 25 kJ/cm~2 and irradiances spanning 4 × 106-10~(14) W/cm~2. Single pulse hole depths range from 84 nm to 147 μm. A one-dimensional thermal model establishes a set of nondimensional variables for hole depth, fluence, and pulse duration. For pulse durations shorter than the radial diffusion time, the hole depth exceeds the thermal diffusion length by a factor of 1 to 30 for more than 90% of the data. For pulses longer than this critical time, transverse heat conduction losses dominate and holes as small as 10~(-3) times the thermal diffusion depth are produced. For all cases, the ablation efficiency, defined as atoms removed per incident photon, is 10(-2) or less, and is inversely proportional to volume removed for pulse durations less than 100 ns. At high fluences, more than 10 to 100 times ablation threshold, explosive boiling is identified as the likely mass removal mechanism, and hole depth scales approximately as fluence to 0.3 to 0.4 power. The power-law exponent is inversely proportional to the shielding of the laser pulse by ejected material, and shielding is maximum at the 1-ns pulse duration and minimum near the 1-μs pulse duration for each material. Using the thermal scaling variables, the high-fluence behavior for each material becomes strikingly similar.