THz-driven nonlinear intersubband dynamics in quantum wells

In this work, we demonstrate the direct observation of non-equilibrium intersubband dynamics in a modulation-doped multiple quantum well sample induced by intense terahertz pulses. The transmission spectra show a clear dependence on the incident THz field strength, which gives rise to a multitude of nonlinear optical effects that go beyond the standard textbook two-level description of light-matter interaction. Of special interest is thereby the multiple octave spanning bandwidth of the used single-cycle THz pulses, which allows the phase-locked coupling of adjacent intersubband transitions. Examples of this interaction include the efficient, coherent population transfer, the THz induced undressing of collective excitations, and the THz Stark effect. (C) 2012 Optical Society of America