Two phases in, one complex amplitude out

Drag ψ. The two blue phase-only phasors (Capasso, PRL 2017) open apart; the amber resultant complex amplitude (Yu, LSA 2019) scales as cos ψ. ψ is the double-phase pivot.

ψ = 24° θ + ψ = 84° θ − ψ = 36° phase θ = 60° (target phase) amplitude = cos ψ = 0.91 ψ→0: full amplitude · ψ→90°: phases cancel
24°