Abstract
The nonlinear mixing of near-infrared (NIR) and terahertz (THz) laser beams is investigated experimentally in a square quantum well structure, where the symmetry of the sample can be controlled by applying an electric field along the growth direction. The mixing produces sidebands, which appear at , where . For a given frequency, the intensity of the sidebands displays two main resonances as a function of the NIR frequency. These resonances are separated by the frequency. Their intensity is found to depend strongly on the electric bias and on frequency. The sideband intensity is zero when the sample is unbiased and increases significantly with bias. The sideband is strong when the laser frequency is tuned in resonance with an intersubband transition and also at low frequencies. The main features of our results are explained qualitatively, except at very high intensities, by a perturbative model of the nonlinear susceptibility . At high intensities, the resonances are observed to red shift and broaden.
- Received 23 February 2004
DOI:https://doi.org/10.1103/PhysRevB.70.115312
©2004 American Physical Society