16-microm infrared generation by difference-frequency mixing in diffusion-bonded-stacked GaAs.

Tunable 90-ps 15.6-17.6-microm coherent radiation was generated by means of difference-frequency mixing in diffusion-bonded-stacked GaAs. The sample consisted of 24 alternately rotated layers with a total length of 6 mm and with low optical loss to achieve third-order quasi-phase matching. The wavelength-tuning curve was close to the theoretical prediction, demonstrating that the bonding process maintained nonlinear optical phase matching over the entire interaction length. Maximum conversion efficiency of 0.7%, or 5% internal quantum efficiency, was measured at 16.6 microm, consistent with the theoretical predictions.