Temperature and wavelength tuning of second-, third-, and fourth-harmonic generation in a two-dimensional hexagonally poled nonlinear crystal

Using high-power nanosecond pulses, we measured the second-harmonic conversion efficiency of two-dimensional hexagonally poled lithium niobate as a function of temperature and wavelength. These results were compared with theoretical estimates and with measurements in one-dimensional periodically poled lithium niobate. We found that for a substantial range of parameters a two-dimensional noncollinear interaction has a broader tuning response than a one-dimensional collinear interaction. We also observed and characterized third- and fourth-harmonic generation processes in the same crystal.