Tailoring Single-Helicity Harmonics via Valley Interference in Monolayer MoS₂ with Counter-Rotating Two-Color Circular Laser Pulses

Based on 2D semiconductor Bloch equation simulations, we demonstrate tunable high-order harmonic generation in monolayer MoS₂ driven by counter-rotating two-color circular laser pulses. Single-helicity harmonic generation is achievable: tuning the fundamental-to-second-harmonic field amplitude ratio suppresses left-handed plateau harmonics, yielding dominant right-handed emission. Valley-resolved analysis attributes this to destructive interference between K/K′-valley harmonics along both x and y axes. Further adjustment of the amplitude ratio and field rotation angle reverses the helicity, switching to left-handed dominance and enabling on-demand helicity control. This work deciphers the valley-interference mechanism governing circular harmonic generation in 2D transition-metal dichalcogenides, pioneering a pathway to single-helicity harmonics and solid-state circular attosecond pulses.