Fig. 1. Schematic of the experimental setup

Fig. 2. SEM images of two-dimensional periodic micro- and nano-scale composite structures formed on tungsten surfaces when the linearly polarized femtosecond laser irradiates with the pulse number of 20

Fig. 3. SEM images of two-dimensional periodic micro- and nano-scale composite structures on the tungsten surfaces induced by linearly polarized femtosecond laser pulses when the overlapped pulse number is 50, 100, 150, respectively

Fig. 4. Measured variations of the periodicity and ridge width for the subwavelength ripple structures on the tungsten surfaces with the overlapped pulse number of the linearly polarized femtosecond laser

Fig. 5. SEM images of two-dimensional micro- and nano-scale composite structures on tungsten surface induced by azimuthally polarized femtosecond laser beam with different pulses. (a) N=20; (b) N=50; (c) N=100; (d) N=200

Fig. 6. Measured pulse number dependent area of two-dimensional composite structures on tungsten surfaces induced by femtosecond laser with either linear or azimuthal polarization