We demonstrate difference frequency generation (DFG) of 8.66–11.34 &mgr;m wavelength light in intersubband InGaAs/AlAs quantum wells by mixing of 1.92 &mgr;m±25 nm and 2.39 &mgr;m±39 nm. The peak DFG second order nonlinear susceptibility &khgr;(2)is measured to be 12±1 nm/V, more than 65 times that of GaAs, at a difference frequency output wavelength of 9.50 &mgr;m. The intersubband absorption for the 1–2 and 1–3 transitions is measured to be 9.3 and 2.1 &mgr;m, respectively. Second harmonic generation (SHG) of 4.76, 5.12, and 5.36 &mgr;m light with a CO2laser is observed with a peak SHG &khgr;(2)of 52±3 nm/V. Good agreement of experiment with theory is found for both the linear and nonlinear optical properties. This demonstration of mid‐infrared DFG opens the possibility for monolithic diode laser pumps and compact waveguide frequency converters as tunable midinfrared sources. ©1995 American Institute of Physics.