Generation of frequency-tunable far-infrared and terahertz radiation by optical nutations at intraband transitions in asymmetric semiconductor nanoheterostructures

A frequency-tunable emitter of far-infrared and terahertz radiation utilizing optical nutations at intraband transitions in semiconductor nanoheterostructures with asymmetric quantum wells excited by femtosecond electromagnetic pulses is suggested and analyzed in detail. Since quantum-confinement sub-bands in such structures possess differing mean dipole moments, nutations involving intraband transitions between these subbands result in the appearance of low-frequency polarization that serves as the source of infrared or terahertz radiation. If, rather than being excited homogeneously along the structure, the nutations are characterized by some spatial period, then, in spite of the pulse character of the excitation, the emitted radiation will be continuous-wave. The radiation frequency can be tuned in a broad range by changing the spatial period or the repetition rate of the femtosecond pulses.