Secondary electron yield engineering of copper surfaces using ultra short infrared laser pulses

Abstract

The texturing of copper surfaces with ultrashort laser pulses leads to microscopic groove formation but results also in nanostructure development at the surface. Both structure types, micro- and nanostructures, are influenced by the laser processing parameters such as the laser power, the scanning speed, the repetition rate, and the line spacing. The generated nanostructures determine mainly the macroscopic properties of the laser-modified copper surface such as the optical reflectivity as well as the secondary electron yield (SEY). To study these effects, polycrystalline copper surfaces were irradiated with infrared picosecond laser radiation (wavelength of 1064 nm, pulse duration of 12 ps, repetition rate of 100 kHz and 1 MHz, respectively) and the secondary electron yield, as well as morphology and shape of the formed nanostructures were analyzed by scanning electron microscopy. The impact of the laser processing parameters on morphology and SEY show the effect of the nanostructures. From these correlations, the reduction of the SEY with increasing accumulated laser fluence and decreasing scanning speed has been identified as a general trend. Especially at high laser power (< 1.9 W) and low scanning speed (< 20 mm/s), the irradiation leads to the formation of compact nanostructures that results in surfaces with a SEY maximum as low as 0.7. SEY values lower than unity are interesting for practical applications of SEY reduction in particle accelerators. Fast processing is necessary to fulfil the technical and technological demands of the deployment and the fabrication of advanced accelerator components. Based on the results, a productivity of ~ 110 s/cm² for SEY ≤ 1 can be estimated at a laser power of 15 W.