RESONANT HARMONIC-GENERATION AND DYNAMIC SCREENING IN A DOUBLE-QUANTUM-WELL

Second- and third-harmonic generation are observed in a semiconductor heterostructure which approximates a two-state system with an 11-meV l evel spacing. A resonance in the second- (third-) harmonic generation is found when the depolarization-shifted infrared absorption peak is S tark tuned through 2 (3) times the pump frequency. These resonances ar e thus associated with the depolarization-shifted, and not the bare, i ntersubband energy. Data are analyzed with a theory of second-harmonic generation including dynamic screening. Saturation is observed at pum p intensities > 10 kW/cm2.