We present a pulsed RGB source based on cascaded nonlinear processes that occur inside
a single crystal of PPLN with two poling periodicities placed in tandem. The first periodicity
produces a~ 1.43 μm signal through optical parametric generation and the last section
simultaneously produces the second (near-IR) and third harmonic (blue). The green is
produced by second harmonic generation of the pump and the red is produced by non-
phase-matched sum-frequency generation between the signal and pump beam.

Quasi-phase-matched second harmonic generation and third harmonic generation through
sum-frequency generation can occur simultaneously if the poling periodicity of the nonlinear
medium satisfies Lambda= lambda/(2 (n 2omega-n omega)) and Lambda= 3lambda/(3n
3omega-2n 2omega-n omega) where lambda is the wavelength of the fundamental beam
and n omega, n 2omega, n 3omega are the refractive indices of the three waves; we have
assumed first and third-order quasi-phase-matching for the second and third harmonic …