Carrier-wave Rabi flopping on radiatively coupled shallow donor transitions in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>n</mml:mi></mml:math>-type GaAs

Abstract

Ultrafast phase-resolved terahertz propagation experiments reveal the nonlinear optical response of shallow donor transitions in $n$-type GaAs. At a lattice temperature of $100\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, carrier-wave Rabi oscillations between bound impurity levels govern the nonlinear terahertz response for terahertz driving fields up to $5\phantom{\rule{0.3em}{0ex}}\mathrm{kV}∕\mathrm{cm}$. The radiative coupling between impurity transitions results in a coherently excited macroscopic $1S\text{\ensuremath{-}}2P$ polarization that oscillates for several picoseconds. A comparison with the Bloch equations for radiatively coupled two-level systems demonstrates a breakdown of the two-level approach for field amplitudes above $5\phantom{\rule{0.3em}{0ex}}\mathrm{kV}∕\mathrm{cm}$.