## 3 Results
### 806 nm Pump
In these experiments, the femtosecond pulses were delayed with respect to those from the Nd: YAG laser to propagate through the formed plasma at a maximal density of the ejected particles. The synchronization of the femtosecond and nanosecond lasers was accomplished using a digital delay generator, and the delay between the HP and the DP was varied in the range of 0 to 1000 ns. We were also able to analyze the plasma and harmonic dynamics at high delays, spanning from a few units to several hundred microseconds. However, apart from the delay region, in which strong harmonics were observed (100-300 ns, Figure 3A), no harmonics appeared in the microsecond-long delays, thus pointing out the absence of the influence of large mass species on the whole yield of harmonic emissions from the tin LIP. The application of the TCP to this plasma led to the appearance of a rather stronger difference between the whole set of harmonics and one of them, which was attributed to the influence of a resonance-induced mechanism of the enhancement of a single harmonic in the vicinity of the strong transition of tin ions. In the case of the 0.2 mm-thick BBO, some temporal delay between 806 and 403 nm pulses in the LIP still allowed for the effective interaction, leading to the odd and even harmonics generation, since the trailing part of the second harmonic wave overlaps with the leading part of the 806 nm wave (Figure 3B). Another spectrum appeared in the case of the installation of 0.5 mm-thick BBO on the path of the DP. The harmonic distribution became notably heterogeneous due to an insufficient overlap between the 806 nm and 403 nm pulses, delayed from each other by 95 fs in the plasma area, resulting in the generation of 2(2n + 1) harmonics (H10, H14, H18, and H22), while other even harmonics, corresponding to 4(n + 1) orders (H12, H16, and H20), were almost suppressed. The most important finding in these TCP studies was the appearance of an exceptionally strong 18 th harmonic (upper panel of Figure 3B) notably exceeding the above-analyzed 17 th harmonic achieved during the SCP of the Sn LIP. Moreover, second-order diffraction of this harmonic caused a stronger image of H9 (upper right arrow), leading to the impression that H9 became stronger in the case of the TCP compared with the SCP (bottom panel of Figure 3B). The prevalence of H18 over H17 could have been caused by a stronger involvement of the resonance processes in the enhancement of the former harmonic emission. The wavelength of this harmonic (H18, \(\lambda\) = 44.8 nm, E = 27.68 eV) was closer to some 4d\({}^{10}\)5s\({}^{2}\)5p\({}^{2}\)P\({}_{3/2}\)\(\rightarrow\)4d\({}^{9}\)5s\({}^{2}\)5p\({}^{2}\) ionic transitions of tin, possessing strong oscillator strengths (gf). In the meantime, the gf of one of those transitions [4d\({}^{10}\)5s\({}^{2}\)5p\({}^{2}\)P\({}_{3/2}\)\(\rightarrow\)4d\({}^{9}\)5s\({}^{2}\)5p\({}^{2}\) (\({}^{1}\)D)(\({}^{2}\)D\({}_{5/2}\))], at the wavelength of 47.20 nm, has been calculated to be 1.52, and this value is five times larger than other transitions from the ground state of Sn II [45]. From this point of view, one can expect an almost perfect coincidence of an H17 (\(\lambda\) = 47.4 nm) and 4\({}^{10}\)5s\({}^{2}\)5p\({}^{2}\)P\({}_{3/2}\)\(\rightarrow\)4d\({}^{9}\)5s\({}^{2}\)5p\({}^{2}\) (\({}^{1}\)D)(\({}^{2}\)D\({}_{5/2}\)) transition, and stronger enhancement compared with H18. However, our experiment showed the reverse case when H18 is much stronger than H17. A few reasons could be responsible for this contradiction. The presence of an even stronger ionic transition of Sn II in the 44 nm range of the XUV spectrum can cause a larger enhancement of H18 with respect to H17. Additionally, the Stark shift of transitions can modify their influence on the harmonic yield. Another option could be the involvement of the Sn III ions [43]. Some of them lie in the vicinity of H18 and their oscillator strengths (gf\(\sim\)0.5) are high enough to cause the resonance enhancement of nearby harmonics.