High harmonic generation is a phenomenon that occurs when an atom is subjected to a strong laser field. The laser field must have an intensity of at least \({10}^{14}\) \(\mathrm{W}/{\mathrm{cm}}^{2}\) to cause tunnel ionization, which releases an electron from the nucleus and allows it to gain energy by moving in the laser field. Upon recombining with the parent ion, the electron radiates its kinetic energy as photons in the XUV region. In this study, In order to find the optimal intensity of each atom, we first simulate and investigate the ionization probability of the noble gas atom. The simulation results show that the saturation intensity of tunnel ionization is about 3.8, 6, 8.1 and 12.5 × \({10}^{14}\) \(\mathrm{W}/{\mathrm{cm}}^{2}\) for xenon, argon, neon and helium gases, respectively. Using these results, we have been able to obtain the appropriate intensities to produce optimal attosecond pulses for each atoms. Then, according to the saturation intensity of gas ionization, we simulate the high-order harmonic spectrum in three intensities of 3, 5, and 8 × \({10}^{14}\) \(\mathrm{W}/{\mathrm{cm}}^{2}\) and investigate the effects of atomic and laser parameters on the cut-off point and plateau region of high harmonic generation spectrum. The simulation results show that the intensity and time profile of attosecond pulses are highly dependent on \({I}_{P}\), and only the atoms that are in the range of tunnel ionization produced attosecond pulses. Also, our simulation results indicate that increasing the intensity leads to higher cut-off points and plateau regions for the harmonics. Furthermore, we found that helium had the highest cut-off point and plateau region at all three intensities, making it the most efficient noble gas for high harmonic generation.

高次谐波的产生是原子受到强激光场作用时发生的现象。激光场的强度必须至少为 \({10}^{14}\) \(\mathrm{W}/{\mathrm{cm}}^{2}\) 才能引起隧道电离，从而释放出来自原子核的电子，并使其通过在激光场中移动来获得能量。与母离子重新结合后，电子在 XUV 区域以光子的形式辐射其动能。在本研究中，为了找到每个原子的最佳强度，我们首先模拟并研究惰性气体原子的电离概率。模拟结果表明，隧道电离的饱和强度约为3.8、6、8.1和12.5 × \({10}^{14}\) \(\mathrm{W}/{\mathrm{cm}}^{2 }\) 分别用于氙气、氩气、氖气和氦气。利用这些结果，我们已经能够获得适当的强度，为每个原子产生最佳的阿秒脉冲。然后，根据气体电离的饱和强度，模拟3、5、8×\({10}^{14}\)\(\mathrm{W}/{三种强度下的高次谐波谱\mathrm{cm}}^{2}\) 并研究原子和激光参数对高次谐波产生光谱的截止点和平台区域的影响。模拟结果表明，阿秒脉冲的强度和时间分布高度依赖于\({I}_{P}\)，并且只有处于隧道电离范围内的原子才会产生阿秒脉冲。此外，我们的模拟结果表明，增加强度会导致谐波的截止点和平台区域更高。此外，我们发现氦气在所有三种强度下都具有最高的截止点和平台区域，使其成为产生高次谐波的最有效的惰性气体。