Study on the Thermal Radiation Characteristics of Tungsten Surface Grating Structures Prepared by Femtosecond Laser Direct Writing

In this paper, using laser direct writing technology, a femtosecond laser was used to process a periodic grating structure on a 99.99% tungsten target. The specific parameters of the laser are as follows: a center wavelength of 800 nm, pulse width of 35 fs, repetition rate of 1 kHz, and maximum single pulse energy of 3.5 mJ. The surface morphology of the samples was characterized and analyzed using a scanning electron microscope (SEM, Coxem, Republic of Korea) and atomic force microscope (AFM, Being Nano-Instruments, China). The thermal radiation infrared spectrum of the tungsten target with grating structures was measured using a Fourier transform infrared spectrometer (Vertex 70, Bruker, Germany). The results show that as the laser fluence increases, the depth of the groove, the width of the nanostructure region, and the width of the direct writing etching region all increase. The peak thermal radiation enhancement appears around the wavenumber of 900 cm−1 when the laser fluence is sufficient. Additionally, its intensity initially increases and then decreases as the laser fluence increases. If the grating period is too large, the impact on thermal radiation is not clear. The heating temperature significantly affects the intensity of thermal radiation but does not have a noticeable effect on the position of thermal radiation peaks. Moreover, the relative weighting of different wavenumbers changes as the temperature increases.