Highly efficient infrared optical nonlinearity of a wide-bandgap chalcogenide Li_2CdGeS_4

A quaternary chalcogenide Li(2)CdGeS(4) is an excellent candidate for a nonlinear optical (NLO) material exhibiting wide transparency spanning from its fundamental band edge (3.15 eV) to the terahertz regime (23.5 μm). Strong optical nonlinearity of Li(2)CdGeS(4) has been investigated over a wide spectral range (λ=1.064-3.3 μm) based on second- and third-harmonic generation. The compound has a high damage threshold at λ=1.064 μm because of saturable three-photon absorption, and is phase-matchable for λ>1.5 μm with χ(2) ≃50 pm/V. It also exhibits strong third-order nonlinearity of χ(3) ≃10(5) pm(2)/V(2). Li(2)CdGeS(4) is promising for high-power NLO applications in the broad infrared spectrum.