Simple RGB source based on simultaneous quasi-phase-matched second and third harmonic generation in periodically poled lithium niobate

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 generation, respectively. For most materials at a given temperature, these equations can only be satisfied for one poling periodicity and one pump wavelength, which for LiNb03 are lambda = 1.43 mum and Lambda = 15.3mum. We used this principle to create a source of red, green and blue light (RGB source) (Robles-Agudo et al, 2006). The device consists of a single crystal of PPLN with two periodicities pumped by the common 1.064 mum line of a Nd:YAG laser.