通过数值求解一维短程势含时薛定谔方程,研究了初始粒子数布居对谐波辐射的影响.结果表明,当中等强度的激光(10～(14)W/cm～2)作用于具有较高电离能的原子或离子时.如果初始粒子数全部位于基态,这时的原子或离子不发生电离,只能得到低次谐波.如果部分粒子位于基态而部分粒子位于激发态.这时高次谐波增强,低次谐波受到抑制,原子发生部分电离,当初始粒子数全部位于激发态时,谐波转换效率降低,谐波次数减少,原子全部电离,这说明部分电离有利于谐波辐射,在一定程度上证明了半经典两步模型的假设.

By solving the time-dependent Schrodinger equation with a one-dimensional short range potential, the effect of initial population on the high harmonics generation was studied. The results reveal that when a moderate intensity laser acts on an atom or ion of high ionizational potentials, if the initial population is on the ground state, the atom or ion will not be ionized, only lower harmonics can be obtained. If the initial population is partily on the ground state and partly on the excited states, the atom will be ionized partily, and the lower harmonics will be weak and the high harmonics be increased. If the initial population is on the excited states, the atom will be ionized completely, and the orders and the conversion efficiency will be lower. These results show that partial ionization of the atom will enhance the harmonic generation, and the two-step semiclassical model is confirmed to some extent.