Infrared phase-conjugate reflection by hot electron-induced optical nonlinearity in n-Ge

We have studied backward-degenerate four-wave mixing at CO₂ laser wavelengths in n-type Ge having a free electron density of N=5×10¹⁶ cm^-3. The phase conjugation due to the redistribution of free electrons between the equivalent valleys was observed. The effect occurs only when the electric field E of the light wave is aligned nonsymmetrically relative to the long axes of the valleys in the crystal, and is related to carrier heating by the infrared radiation. Received: 11 April 2000 / Revised version: 13 September 2000 / Published online: 10 January 2001