Second harmonic generation (SHG) from resonant GaAs gratings

We study SHG in nonlinear (NL), GaAs gratings. We find large enhancement of conversion efficiency when the pump field excites the guided mode resonances (GMRs)of the grating. Under these circumstances the spectrum near the pump wavelength displays sharp resonances characterized by dramatic enhancements of local fields and favorable conditions for second harmonic generation, even in regimes of strong linear absorption at the SH wavelength thanks to the phase-locked (PL) component of the SH. In particular, in a GaAs grating pumped at 1064nm, we predict SH conversion efficiencies approximately five orders of magnitude larger than conversion rates achievable in either bulk or etalon structures of the same materials.