Second-order susceptibility in asymmetric quantum wells and its control by proton bombardment

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Abstract
We report measurements of extremely large mid-infrared second-order susceptibilities due to intersubband transitions in an asymmetric quantum well, and selective suppression of these susceptibilities by proton bombardment of the sample. The measured second-order susceptibility for second-harmonic generation of 9.25–10.78 μm is in good agreement with theoretical calculations based on measured infrared absorption spectra, which show the lowest two intersubband transitions. The peak value of the susceptibility is 58 nm/V, 320 times larger than the bulk nonlinear susceptibility of GaAs.