Polarization oscillations in coupled quantum wells-a scheme for generation of submillimeter electromagnetic waves

It is shown that, in a specially designed coupled quantum-well (QW) system, it is possible to prepare an initial nonstationary electronic state selectively by interband photoexcitation in one of the wells. Excited electrons oscillate between the two wells, giving rise to an oscillating electric dipole moment. In a stacked system of identical QW pairs, these dipoles add up, producing a tangible alternating voltage which can be used to modulate the incident radiation intensity. Therefore, with a properly designed positive feedback loop connecting the coupled QW system and the light modulator, it is possible to generate self-excitation of dipolar oscillations. This provides a new method of generating submillimeter electromagnetic waves, accompanied by ultrashort optical pulses at terahertz frequencies