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In this paper, we compare the theoretical performance of two design methods that allow simultaneous phase matching of two arbitrary X(2) processes along with the capability of adjusting their relative strength. The crystal of these 1-D aperiodic gratings is chosen to be the orientation-patterned gallium arsenide (OP-GaAs), which has been recently used in several devices for high power infrared beam generation. These single gratings placed in an optical parametric oscillator (OPO) or an optical parametric generator (OPG) can simultaneously phase match two optical parametric amplification (OPA) processes, OPA-1 and OPA-2, for converting the 2.1-μm pump laser radiation into the long-wave infrared (8-12 μm) in an idler-efficiency enhanced scheme. The first aperiodic grating design method (Method-1) relies on generating an aperiodic grating structure that has domain walls located at the zeros of the summation of two cosine functions each of which has a spatial frequency that equals one of the phase-mismatches of the two processes. In this method some of the domain walls are discarded considering the minimum domain length (Dmin) that is achievable in the production process. The second design method (Method-2) relies on discretizing the crystal length with samples with a length that is much smaller than Dmin and testing each sample’s contribution in such a way that the sign of the nonlinearity maximizes the magnitude sum of the real and imaginary parts of the Fourier Transform of the grating function at the relevant phase-mismatch spatial frequencies. Also, during the procedure, the smallest domain length is imposed to be Dmin. In this paper, we present the results of Method-2 which we find that it produces a similar performance as Method-1 in terms of the maximization of the magnitudes of the Fourier peaks located at the phase-mismatches of the nonlinear processes while adjusting their relative strength. To our knowledge, we are the first to propose such aperiodic OP-GaAs gratings for efficient long-wave infrared beam generation based on simultaneous phase matching.
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