Fabrication of S-shaped micron-sized constrictions on FeC (steel) surface using femtosecond laser ablation with beam shaping

In this paper, we demonstrate the fabrication of S-shaped micron-sized constrictions on steel (Fe3CII) surface using the femtosecond laser ablation technique. The femtosecond laser used has a wavelength of 775 nm, a power range of 0–1000 mW, a pulse duration of 130 fs, and a pulse repetition rate of 1–2 kHz. The ultra-low-pulse duration of 130 fs enables ablation of material surfaces without excessive thermal heating of the material around the zone of ablation. This becomes useful when ablating materials that are thermally sensitive such as superconducting thin films. This practice run of ablating S-shaped micron-sized constrictions on steel surfaces shown in this paper will enable one to use the same technique in ablating micron- and nano-sized structures on superconducting thin films without thermally altering the superconductive film. In this paper, S-shaped micron-sized constrictions on steel were fabricated with a constriction width of 37.1 and 47.3 μm whose images were created using an optical microscope (OM) and S-shaped micron-sized constrictions with a constriction width of 30.8 and 35.2 μm whose images were created using an atomic force microscope (AFM). The reduction in the constriction widths was achieved by reducing the laser ablation width or laser ablation spot size and then bringing the laser ablation spots closer together in G-code program. The reduction of the laser ablation width is achieved by reducing the laser fluence applied closer to the ablation threshold of steel and by using laser beam shaping techniques such as beam collimation and beam focusing.