Continuous wave optical properties in dc-biased nanostructure semiconductors driven by a THz-field

The optical response of biased nanostructure semiconductors with a THz field are studied by calculating absorption spectra based on semiconductor Bloch equations. We investigate dependence of absorption spectra on the relative phase between optical pulses and THz field and continuous wave optical properties using short pulse technique. All of the absorption spectra have Stark ladder structures with energy spacing, mℏω_b + m′ℏω_L. There are actually frequency range where there is gain for various phases. But, there is no gain region in the continuous wave absorption spectrum. The optical gain without population inversion results from the nonlinear sum and difference mixing of the optical and the THz frequencies via the phases.