We report type I second-harmonic generation by use of first-order quasi-phase matching in a GaAs/AlAs symmetric superlattice structure with femtosecond fundamental pulses at 1.55 microm. Periodic spatial modulation of the bulklike second-order susceptibility chi(zxy)(2) was achieved with quantum-well intermixing for which the group III vacancies were created by As+-ion implantation. A narrow second-harmonic bandwidth of approximately 0.9 nm (FWHM) with an average power of approximately 1.5 microW was detected, corresponding to an internal conversion efficiency of approximately 0.06%, which was considerably limited by the spectral bandwidth of the fundamental.

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We acknowledge ®nancial support of the Deutsche Forschungsgemeinschaft and of Roche Diagnostics. P. Go Èttig and R. Ramachandran helped with biochemical analyses. We thank G. Bourenkov and H. Bartunik, and G. Leonard for help with synchrotron data collection at DESY BW6 (Hamburg) and ESRF ID14-4 (Grenoble), respectively.