Melting Thresholds of Aluminum Irradiated by Ultraviolet Laser Pulses for Periodic Nanostructures Formation

For laser ablation of aluminum, ultraviolet Nd:YAG lasers were used with wavelengths of 355 nm and 266 nm (pulse durations of 5 ns and 6 ns, respectively, at repetition rate of 10 Hz).The melting threshold of aluminum was measured to be Fth,355 = 1.51 J/cm for 355 nm and Fth,266 = 0.76 J/cm for 266 nm.Periodic nanostructures were successfully produced on aluminum surfaces in the vicinity of laser-produced grooves.For the 355 nm laser, the structures formed at a fluence of 1.7 J/cm to 2.2 J/cm with the number of pulses N = 200 to 2000.The interspace of periodic nanostructures was 568 nm, as determined by 1D-fast Fourier transform on the average of 10 points.The depth of periodic nanostructures measured by atomic forced microscopy was 90 nm to 160 nm.For the 266 nm laser, the periodic nanostructures formed at a fluence of 1.0 J/cm to 3.0 J/cm with the number of pulses N = 300 to 500.The interspace of periodic nanostructures was 474 nm on average.The periodic nanostructures were oriented orthogonally to direction of laser polarization.