Generation of Near-Circularly Polarized Attosecond Pulse with Tunable Helicity by Unidirectionally Rotating Laser Field

A method to produce circularly polarized attosecond pulses with tunable helicity from CO molecule by using an unidirectionally rotating laser field is proposed. It is found that broadband harmonic supercontinuum with circular polarization can be generated from the oriented CO molecule. This enables the production sub-100 attosecond isolated pulse with the ellipticity as high as 0.9 at the macroscopic level. Moreover, the helicity of the generated high-order harmonics and the attosecond pulse can be tuned by adjusting the orientation of the CO molecule. This method will be beneficial for the studies on chiral-specific dynamics and magnetic circular dichroism on an attosecond time scale.