线偏振激光场中分子高次谐波椭偏率的调控

高次谐波椭偏率的调控为人们研究磁性材料和手性介质中的超快动力学过程提供了有效途径.本文理论研究了线偏振激光脉冲驱动下，H₂~+和H₃²⁺分子高次谐波的偏振特性及阿秒脉冲产生.结果表明当取向角为0~o时，H₂~+分子谐波的椭偏率几乎为0,而H₃²⁺分子谐波具有较大椭偏率，这是由于分子轨道对称性决定的.通过改变取向角的大小，可以调控高次谐波强度以及谐波椭偏率大小，为产生椭偏XUV脉冲提供了手段.同时，发现椭偏率较大的谐波阶次对应的谐波强度较小，分析表明分子的双中心干涉效应对椭偏率有很大的影响.对于H₂~+和H₃²⁺分子，分别合成了椭偏率为0.75和0.55的椭圆偏振阿秒脉冲.这种大椭偏XUV脉冲的产生为高次谐波在材料与生物科学领域提供了重要应用.

Control of ellipticity in molecular high-order harmonic generation in a linearly polarized two-color laser field

The control of elliptically polarized harmonic provides an effective route t for probing and manipulating the ultrafast magnetic and chiral dynamics. We theoretically investigate the high-order harmonic generation (HHG) and attosecond pulse of H2+ and H32+ molecules driven by linearly polarized laser pulses. When the orientation degree is zero, the harmonic ellipticity of H2+ molecules is almost zero. While for H32+ molecules, the harmonic ellipticity is larger, which is determined by the symmetry of molecular orbitals. We find that the harmonic intensity and harmonic ellipticity can be controlled by changing the orientation degree, which provides a means to generate large elliptical XUV pulses. The harmonic order with higher ellipticity corresponds to the order with lower harmonic intensity. The analysis shows that the two-center interference effect of molecules has a great influence on the ellipticity. For H2+ and H32+ molecules, elliptically polarized attosecond pulses with ellipticity of 0.75 and 0.55 are synthesized, respectively. The generation of large elliptical XUV pulses provides important applications of high order harmonic spectrum in materials and biological sciences.