## 3 Results
### 806 nm Pump
Neutral emission peaks were not evident at early times in the case of the ns-induced plasma spectra and required longer delays to appear. Additionally, they showed lower intensities compared to the ionic emissions at the early stages. This is attributed to a higher population of the charged ions emitting in the visible region compared to the neutral atoms, though once these ion populations decreased due to recombination processes in the LIP, at later times the emissions from neutral species became a dominating factor. Images in the case of the time delays above 100 ns show a small, expanded laser plume up to a distance of 1.2 mm from the surface of the bulk tin. Due to high brightness, we suppressed emissions by placing neutral filters in front of the ICCD camera. At a period of 200 ns from the ablation, the fastest components of plasma expanded up to a distance up to 2.5 mm. However, their role in harmonic generation is questionable due to a small concentration of these fast components of LIP. We analyzed the images of plasma up to 2000 ns from the beginning of ablation, when a weak, low-dense cloud of plasmas was still seen in the images. The second method of the plasma dynamics studies was based on the analysis of the variations of harmonic emissions at different delays between the HP and the DP using a two-laser (Ti: sapphire and Nd: YAG) configuration. In this case, HHG spectra from Sn plasma were recorded at different delays between a 10 ns HP and a 64 fs DP. The intensity dependencies of the 11 th (H11) and 15 th (H15) harmonics on the delay between the HP and the DP are shown in Figure 3A. For this plasma, the maximum delay up to which we were able to observe HHG emission was equal to \(\sim\)500 ns, at which a very weak emission of the lowest recorded harmonic (H9) was still seen in the XUV spectrum. We observed the clearly determined maximal yields of both H11 and H15 at the same (\(\sim\)150 ns) delay from the beginning of ablation. This pattern can be explained by the presence of the same type of emitters within the whole period of observation, when a decrease of plasma density, due to its expansion, causes the decay of the harmonic yield. The velocity of these emitters, according to optimal delay, can be estimated at \(\sim\)1.3 \(\times\) 10\({}^{3}\) m/s, taking into account the 0.2 mm distance between the target and the axis of DP propagation. Notice that a similar range of the \"optimal\" delays (140-200 ns) between the HP and the DP corresponded to the observation of the maximal harmonic yield in the case of the ablated Sn NP LIP. One can note that during the ablation of bulk Sn, the plasma may contain tin atoms and ions, as well as NPs synthesized during laser ablation. The appearance of Sn nanoparticles was commonly registered at the relatively high fluencies of HP (F \(\approx\) 3 J cm\({}^{-2}\)). The transmission electron microscope (TEM) analysis of the debris deposited on the nearby  
Figure 3: (**A**) Variations of the 11 th (open triangles) and 15 th (filled circles) harmonic yields at different delays between the heating and driving pulses. The fluence of heating pulses on the tin surface was 1.5 J cm\({}^{-2}\). (**B**) Raw images of harmonics in the case of a two-color pump (TCP; 806 nm and 403 nm, upper panel) and a single-color pump (SCP; 806 nm, bottom panel) of tin plasma. Arrows show the maximally enhanced harmonics and their second-order (S.O.) diffractions from the flat-field grating in the case of the two types of pumps. glass substrates while using this fluence of either picosecond or nanosecond HP revealed the presence of sparsely distributed NPs with sizes ranging between 2 and 10 nm. Once again, we emphasize that this mode of plasma formation was unsuitable for generating harmonics in Sn LIP. The use of the fluence F = 1.5 J cm\({}^{-2}\), at which the strongest yield of harmonics from this plasma was achieved, did not reveal the presence of NPs in the deposited debris. Thus, the harmonics, in this case, originated from the atoms and ions of tin.