Chirality-selective second-harmonic response with Floquet engineering.

Floquet engineering in monolayer MoS2 lifts energy degeneracy and yields pronounced chirality-selective second-harmonic generation via nondegenerate optical Stark and Bloch-Siegert shifts.

• Why it matters: Inversion-symmetry breaking can create chiral selection rules, but controlling chirality-selective nonlinear optical responses on ultrafast timescales remains challenging.
• What they did: The study uses sub-bandgap, circularly polarized ultrafast pulses to break time-reversal symmetry and induce chirality-selective optical Stark and Bloch-Siegert shifts, then tunes Floquet-engineered states with pulse intensity and chirality.
• The result: The resulting Floquet-engineered chirality-selective states are finely tunable by optical parameters, enabling controllable nonlinear photonics in MoS2.

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