TAILIEUCHUNG - Lasers Applications in Science and Industry Part 2

Tham khảo tài liệu 'lasers applications in science and industry part 2', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Nanoparticles and Nanostructures Fabricated Using Femtosecond Laser Pulses 11 Fig. 9. Morphological evolution of structures on YBCO thin films induced by linear polarized fs laser with fixed number of pulses N 600 000 and various fluences a F 0 mJ cm2 b F 43 mJ cm2 c F 59 mJ cm2 d F 79 mJ cm2 e F 154 mJ cm2 f F 319 mJ cm2. Inset 2D Fourier spectra transferred from their corresponding SEM images 10 pm 10 pm with pixel resolution of nm . The scale bar is applied to all pictures. Figures 10 a -10 c show the evolution of the ripple structure on YBCO thin films irradiated by a single-beam fs laser with various numbers of pulses N and the fixed laser fluence F 79 mJ cm2. With an increase in the number of pulses the ripple structure became increasingly clear in SEM images as evidenced by the appearance of satellite peaks in the 2D Fourier spectra in the insets of Figs. 10 b and 10 c there are no satellite peaks in the inset of Fig. 10 a for an as-deposited YBCO thin film . The spatial period of ripples estimated from the position of satellite peaks in the 2D Fourier spectra is independent of the number of pulses or irradiation time as shown in Fig. 11 b . Once the number of pulses Ễ 50 000 . the sample surface was irradiated by the 75 mJ cm2 laser pulses for Ễ10 s ripples can be clearly observed on the surface of the sample. In addition the real-time evolution of the ripple structure appears in the transmission measurements in Fig. 10 d . In the case of F 154 mJ cm2 the transmission power of the laser beam dramatically increased to within 2 s and then saturated after 10 s. Some specific points were marked at 79 mJ cm2 of Fig. 10 d and corresponding SEM images are shown in Figs. 10 a 10 b and 10 c respectively. At s . N 500 in Fig. 10 a there are almost no structures on the surface of YBCO thin films. However the rippled structure can be observed at 10 s . N 50 000 in Fig. 10 b meanwhile the transmission power dramatically increased due to the thinning of

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