Tham khảo tài liệu 'advances in solid-state lasers: development and applicationsduration and in the end limits part 13', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 472 Advances in Solid-State Lasers Development and Applications Fig. 6. HHG spectra from tin laser ablation irradiated by femtosecond laser pulse. Strong 17th harmonic nm wavelength is observed. Suzuki et al. 2006 Fig. 7. Intensity of the 17th harmonic nm wavelength as a function of the quarter waveplate angle. The laser polarization is varied from linear 0 degree to circular 45 degree . Suzuki et al. 2006 In Fig. 8 a one sees that the intensity of the 17th harmonic using 795 nm wavelength pump dominates the harmonic spectrum. The intensity of the 17th harmonic is 20 times higher than that of other harmonics. However in Fig 8 b the intensity of the 17th harmonic using 782 nm wavelength pump is decreased and is almost the same as that of other harmonics. In Fig. 8 c the intensity of the 17th harmonic with 778 nm wavelength pump is further decreased. In this case the 17th harmonic intensity is weaker than that of the 13th and 11th harmonics. The above results show that the intensity of the 17th harmonic gradually decreased as the wavelength of the pump laser become shorter. In past work the Sn II ion has been shown to posses a strong transition of the 4d105s25p 2P3 2 - 4d95s25p2 1D 2D5 2 at the wavelength of nm Duffy Dunne 2001 . The gf-value of this transition has been calculated to be and this value is 5 times larger than other transition from ground state High-Order Harmonic Generation from Low-Density Plasma 473 of Sn II. Therefore the enhancement of the 17th harmonic with 795 nm wavelength laser pulse can be explained be due to resonance with this transition. By changing the pump laser wavelength from 795 nm to 778 nm the wavelength of the 17th harmonic is changed from nm to nm. Therefore the wavelength of the 17th harmonic pumped by laser wavelength of 778 nm is farther away from the 4d105s25p 2P3 2 - 4d95s25p2 1D 2D5 2 transition at the wavelength of nm. As a result the resonance condition of the 17th order harmonic is
