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Reflection second-harmonic generation from GaAs/AlAs and GaAs/AlGaAs multilayers

We have observed first-, second- and third-order quasi- phase-matched second-harmonic generation in the reflection geometry from GaAs/AlAs multilayers. We have measured phase- matching curves and identified all the peaks. The linewidth for the first order is limited only by wave-vector mismatch. We have demonstrated two-order-of-magnitude enhancement solely using quasi-phase-matched multilayers. We have also achieved cavity-enhanced quasi-phase-matched second-order and non-phase-matched second-harmonic generation from GaAs/Al0.8Ga0.2As multilayers. We have determined the element of the second-order susceptibility tensor used for quasi-phase matching. We have measured the conversion efficiencies and discussed possibilities for further enhancements.