Abstract
A femtosecond laser system with a frequency of 1 kHz, average power of 185 mW, and wavelength of 800 nm was used in this study to micromachine a polished tungsten block surface. The micro-nanostructure of the tungsten surface was induced via laser and the machined surface roughness was measured with a profiling instrument. The blackened surface sample with periodic fluctuation appeared to be rougher than the polished surface sample. The absorption spectra of the two samples was measured with a spectrophotometer. The average micro-nanostructure tungsten sample absorption was 89% in the range of 380 nm to 1100 nm. The two samples were simulated via the finite difference time domain (FDTD) method; both polished and darkened tungsten models were established based on the experimental measurements. Model absorption with fluctuation structures were over 90% with wavelengths from 380 nm to 1100 nm; i.e., the simulation results were consistent with the experimental results. Two kinds of samples were heated by laser in the wavelength of 976 nm at a 400 W process as temperature changes were measured with tungsten–rhenium thermocouples. The temperature of the blackened tungsten increased at a greater rate than the polished sample at a maximum difference of 88°C. The results suggest that tungsten absorption can be effectively improved by utilizing a periodic and random structure combination on the tungsten surface.
© 2018 Optical Society of America
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