SHG phase-matching: η ∝ sinc²(ΔkL/2); coherence length L_c = π/|Δk|

Franken-Hill-Peters-Weinreich 1961 second-harmonic generation (SHG) in a nonlinear crystal: in the slowly-varying-envelope + undepleted-pump approximation the conversion efficiency as a function of phase mismatch Δk = k(2ω) − 2k(ω) and…