## 3 Theory  
To support our experimental investigations, we used the 1D model described in Ref. [18]. Within this model, the nonlinear medium is simulated by 1D chain of atoms oriented along the propagation direction of laser pulses. The response of each atom in the chain is calculated using the non-perturbative theory [36; 37]. The two-color laser field parameters that were chosen for the single-atom response calculations on one hand coincide with the ones used in the experiments, and on the other hand depend on the position of the atoms in the chain. The generated harmonic radiation from each atom is calculated in the far-field zone by a numerical summation over a chain of atoms [18; 38; 39]. As a result, the spatial distribution of generated radiation is calculated, which is integrated for analysis of the overall intensity of the harmonic radiation. In the numerical calculation we deal with silver plasma having the following parameters related to the above described experimental conditions: density of plasma is equal to \(\sim\)\(2\times 10^{17}\) cm\({}^{-3}\), and the density of free electron is equal to \(\sim\)\(2\times 10^{16}\) cm\({}^{-3}\). Other parameters, such as the intensities of two-color pulses, their durations, and the length of nonlinear medium were chosen to be the same as in experiment. We studied the dependence of harmonic spectra on the size of the individual jet under conditions of the constant length (\(\sim\)5 mm) of nonlinear medium. The number of jets changed with variation of their length. The harmonic spectra are presented in Figure 5a. It is seen that decreasing of \(d\) leads to the shift of \(H_{\text{qpm}}\) towards the shorter wavelength region. The position of \(H_{\text{qpm}}\) as a function of \(d\) is shown in Figure 5b. The results of numerical calculations are shown by open circles. It can be seen that the positions of the center of the enhanced groups of harmonics are inversely proportional to \(d\). Empty and filled squares correspond to experimental data for indium [Figure 2b] and silver (Figure 3) plasmas, respectively. Here we also show some other reported data in the case of silver plasma [40; 41; 42]. The slopes of the dotted lines (\(l=-1\)) correspond to the \(H_{\text{qpm}}\)(Ag) \(\infty\) 1/\(d\) dependence. The data in the case of indium plasma shows similar tendency [(\(H_{\text{qpm}}\)(In) \(\infty\) 1/\(d\)], while the graph is slightly shifted with respect to the data and that is due to the different role of two groups of free electrons in phase mismatch at specific ablation conditions for these two metals. A similar shift has been earlier observed in the case of silver plasma ablated at higher energies of heating pulses (see pentagons in Figure 5b; where the data shown was taken from Ref. [40]). We also investigated the influence of the number of jets on the characteristics of generated radiation. In the numerical investigations we used \(d=0.23\) mm. The calculated spectra are presented in Figure 6a. It can be seen that the harmonic's yield increases with the increase of \(n\). At the same time the maximally enhanced harmonic depended on \(n\). To show it more precisely we analyzed the  
Figure 5: **(a)** Harmonic distribution from silver MJP in the case of propagation of two-color driving pulses (1310 nm + 655 nm) through the plasma of \(\sim\)5 mm length containing the jets with the sizes (\(d\)) equal to 0.15 mm (black empty squares), 0.23 mm (red filled circles), 0.31 mm (blue empty triangles), 0.45 mm (pink filled spheres), and 0.8 mm (green empty rhombs). **(b)** Influence of the jet sizes on the order of maximally enhanced harmonic \(H_{\text{qpm}}\) in the case of silver MJP. Black empty circles correspond to theoretical calculations and green filled squares correspond to experiment with Ag plasma. Triangles, stars and pentagons correspond to earlier reported data for silver plasma [40; 41; 42]. Here we also show the experimental data for indium plasma (blue empty squares). The slopes of all dependences correspond to \(l=-1\).