No abstract

Features of exciton-polariton eigenmodes in a series of light-coupled In 0.04 Ga 0.96 As/GaAs semiconductor multiple quantum wells with varying number of quantum wells N from 1 to 100, and with various periodicities ͑Bragg, near-Bragg, and anti-Bragg͒, are studied in linear measurements of reflection, transmission, and absorption. At Bragg periodicity ͑period dϭ x /2), a photonic band-gap mode grows in amplitude and increases linearly in linewidth with increasing N. The N times increased radiative damping rate is seen to arise from the light character of the eigenmode being swept out of a photonic band-gap structure. The slope of linewidth versus N gives the radiative linewidth of the exciton. Away from Bragg periodicity two branches of energy levels can be resolved in absorption, corresponding to the N exciton-polariton normal modes in the multiplequantum-well structure. Signatures of individual modes becoming optically active are observed in the rich structure of reflection spectra for changing quantum-well periodicity. Antireflection coating of the samples is shown to be an effective way of thus isolating the multiple-quantum-well response.

The nonlinear optical response of semiconductor microcavities in the nonpertubative regime is studied in resonant single-beam-transmission and pump-probe experiments. In both cases a pronounced third transmission peak lying spectrally between the two normal modes is observed. A fully quantized theory is essential for the agreement with the experimental observations, demonstrating that quantum fluctuations leading to intraband polarizations are responsible for this effect.