OPA coupled-wave ODE: dA_s/dz = i*kappa*A_i^*; variation-of-parameters closed form

Optical parametric amplification coupled-wave ODEs. Setup: chi^(2) parametric process pumping a signal A_s at omega_s and idler A_i at omega_i by a strong pump at omega_p = omega_s + omega_i (phase-matched, so Delta-k = 0). Under…