Abstract: We demonstrate the simultaneous generation and internal interference of two second-order parametric processes in a single nonlinear quadratic crystal. The two- frequency doubling processes are Type 0 ( two extraordinary fundamental waves generate an extraordinary secondharmonic wave) and Type I ( two ordinary fundamental waves generate an extraordinary second- harmonic wave) parametric interactions. The phasematching conditions for both processes are satisfied in a single periodically poled grating in {{LiNbO}$_3$} using quasi- phase- matching ( QPM) vectors with different orders. We observe an interference of two processes, and compare the results with the theoretical analysis. We suggest several applications of this effect such as polarization- independent frequency doubling and a method for stabilizing the level of the generated second- harmonic signal.

Keywords: 2nd-harmonic generation; electrode geometries; linbo3; ktp

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