Room-Temperature Macroscopic Coherence of Two Electron-Hole Plasmas in a Microcavity.

Macroscopic coherence of Bose condensates is a fundamental and practical phenomenon in many-body systems, such as the long-range correlation of exciton-polariton condensates with a dipole density typically below the exciton Mott-transition limit. Here we extend the macroscopic coherence of electron-hole-photon interacting systems to a new region in the phase diagram-the high-density plasma region, where long-range correlation is generally assumed to be broken due to the rapid dephasing. Nonetheless, a cooperative state of electron-hole plasma does emerge through the sharing of the superfluorescence field in an optical microcavity. In addition to the in situ coherence of e-h plasma, a long-range correlation is formed between two 8-µm-spaced plasma ensembles even at room temperature. Quantized and self-modulated correlation modes are generated for e-h ensembles in the plasma region. By controlling the distance between the two ensembles, multiple coupling regimes are revealed, from strong correlation to perturbative phase correlation and finally to an incoherent classical case, which has potential implications for tunable and high-temperature-compatible quantum devices.

Transient dual-energy lasing in a semiconductor microcavity.

We demonstrate sequential lasing at two well-separated energies in a highly photoexcited planar microcavity at room temperature. Two spatially overlapped lasing states with distinct polarization properties appear at energies more than 5 meV apart. Under a circularly polarized nonresonant 2 ps pulse excitation, a sub-10-ps transient circularly polarized high-energy (HE) state emerges within 10 ps after the pulse excitation. This HE state is followed by a pulsed state that lasts for 20-50 ps at a low energy (LE) state. The HE state is highly circularly polarized as a result of a spin-preserving stimulated process, while the LE state shows a significantly reduced circular polarization because of a diminishing spin imbalance.

Absolute instrument spectral response measurements using angle-resolved parametric fluorescence.

The broadband parametric fluorescence from a nonlinear crystal can be used as a compact primary source instead of a blackbody for absolute measurements of instrument spectral efficiency. We describe such a setup for measuring the instrument spectral response function in the wavelength range from 450 to 1000 nm. We perform angle-resolved imaging spectroscopy of conical parametric fluorescence in a beta-barium borate crystal pumped by a 405-nm diode laser. The experimental angle-resolved spectra and the generation efficiency of parametric down-conversion agree with a plane-wave theoretical analysis.