Direct measurement of light–matter energy exchange inside a microcavity

We demonstrate that one can directly measure the time evolution of light–matter interaction in a semiconductor microcavity by tracking how the optical response is changed by strong single-cycle terahertz (THz) pulses. A short THz pulse transiently interrupts the interaction of the quantum-well microcavity with the light mode and resets the polaritonic light–matter oscillations at THz frequencies. This THz-reset protocol can provide novel insights into the light–matter coupling dynamics in a wide range of photonic materials such as plasmonic and organic systems.