Quantum interference of multi-orbital effects in high-harmonic spectra from aligned carbon dioxide and nitrous oxide

We investigate experimentally multi-orbital effects in high-order harmonic generation (HHG) from aligned CO_2 and N_2O molecules by intense femtosecond laser fields with linear and elliptical polarizations. For either of the aligned molecules, a minimum in the harmonic spectrum is observed, the position of which shifts to lower-order harmonics when decreasing the intensity or increasing the ellipticity of the driving laser. This indicates that the minimum originates from the dynamic interference of different channels, of which the tunneling ionization and recombination are contributed via different molecular orbitals. The results show that both the highest occupied molecular orbital (HOMO) and low-lying HOMO-2 in CO_2 (or HOMO-1 in N_2O) contribute to the molecular HHG in both linearly and elliptically polarized strong laser fields. Our study would pave a way for understanding multi-electron dynamics from polyatomic molecules irradiated by strong laser fields.

我们通过线偏振和椭圆偏振的强飞秒激光场，对取向的二氧化碳（CO₂）和一氧化二氮（N₂O）分子在高次谐波产生（HHG）中的多轨道效应进行了实验研究。对于这两种取向的分子，都观察到谐波谱中的一个极小值，当降低驱动激光的强度或增加其椭圆率时，该极小值的位置会向低阶谐波移动。这表明该极小值源于不同通道的动态干涉，其中隧穿电离和复合是通过不同的分子轨道贡献的。结果表明，在二氧化碳中的最高占据分子轨道（HOMO）和较低的HOMO - 2（在一氧化二氮中为HOMO - 1）在两种线偏振和椭圆偏振的强激光场中都对分子的高次谐波产生有贡献。我们的研究将为理解强激光场照射下多原子分子的多电子动力学开辟一条道路。