Tuning the orbital angular momentum of high harmonics by manipulating the collinear photon channels in two-color high-harmonic generation

The characteristics of the photon channels in the collinear two-color high-order harmonic generation (HHG) are investigated with the vortices. It is found that the yields of the photon channels sensitively depend on ratio of the intensities I-2 omega/I-omega. This sensitive dependence exhibits unique characteristics such as the suppression of the n-omega fundamental channel and the photon localization in the high-order channel. Therefore, one can adjust I-2 omega/I-omega to select one dominant channel to generate and tune the harmonic vortices with well-defined orbital angular momentum (OAM). Our findings provide an effective way to generate extreme ultraviolet vortices or helical attosecond pulses with well-defined and controllable OAM.