01330nas a2200157   4500008004100000020001400041245007800055210006900133260001100202300001400213490000700227520085100234100002001085700001801105856004901123       1996                        eng d  a0021-897900aNonlinear response of quantum-confined electrons in nonparabolic subbands0 aNonlinear response of quantumconfined electrons in nonparabolic   cAug 15  a2533-25350 v803 a<p>We show that quantum confinement can dramatically alter the density-dependence of the third-order susceptibility, chi(NP)((3)) that arises from band nonparabolicity. Our results predict an oscillatory dependence of the efficiencies for third-harmonic generation and four-wave mixing on the subband occupation of quantum wells, and for narrow wells with high charge densities predict an enhancement over the bulk susceptibility. We also make a simple estimate of the fields required to saturate this nonparabolicity contribution to chi((3)). We discuss these results in light of recent experiments on third-harmonic generation from narrow-gap quantum wells at frequencies of similar to 1 THz, and show that nonparabolicity may not be the only nonlinearity contributing to the large chi((3)) observed. (C) 1996 American Institute of Physics.</p>1 aMarkelz, A., G.1 aGwinn, E., G.  uhttps://markelz.physics.buffalo.edu/node/268