THZ MAGNETOOPTICS OF CHARGE OSCILLATIONS IN COUPLED QUANTUM-WELLS

We have studied the time varying macroscopic polarisation associated w ith charge oscillations in GaAs/AlGaAs asymmetric double quantum wells by coherent detection of the emitted THz radiation. The charge oscill ations are optically excited with femtosecond near infrared radiation and the radiated field is detected by an optically gated photoconducti ng antenna. We discuss the source of the emission; considering the dep endence on pump fluence and excitation wavelength. Magnetic fields app roximate to 1T suppress the emission. For Fields parallel to the quant um well plane the main result is that the electric dipole dephasing ra te increases with increasing field as expected theoretically. In perpe ndicular fields the dephasing rate remains constant but there is an ov erall reduction in the oscillation amplitude which is not presently un derstood.