Nonlinear interactions such as second harmonic generation (SHG)  and sum and difference frequency generation are routinely used for the generation of laser wavelengths. With high power lasers it is necessary to use bulk crystals and tight beam focusing to achieve the maximum conversion efficiency. The use of Quasiphase-matched (QPM) materials such as PPLN and PPKTP are now routinely reported; however, as we will show in this paper, a simple linear QPM crystal does not fully optimize the conversion response. We will report theoretical and experimental results showing that by careful control of the crystal design it is possible to fully compensate for the phase errors associated with the focusing induced Gouy shif
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