J.-K. Rhee

Chirped-pulse amplification of 85-fs pulses at 250 kHz with third-order dispersion compensation by use of holographic transmission gratings

We demonstrate pulse stretching and compression in a high-repetition-rate chirped-pulse Ti:sapphire regenerative amplifier, using high-efficiency holographic transmission gratings. A quantitative dispersion measurement technique is developed to characterize dispersion of the system to the third order. After recompression with third-order dispersion compensation, 3.1-microJ 85-fs, nearly transform-limited pulses are obtained.

Transient carrier and field dynamics in quantum-well parallel transport: From the ballistic to the quasi-equilibrium regime

Femtosecond optical techniques have been used to probe transient electron transport and electric field dynamics in high field parallel transport, in a horizontal p-i-n quantum-well structure. Physical quantities associated with transport transients, such as electron distribution functions, electron velocity, and electron acceleration, have been measured by means of femtosecond absorption saturation, excitonic electroabsorption, and terahertz electromagnetic radiation, at electric fields of up to 16 kV/cm. Important transport phenomena, such as ballistic acceleration on a time scale of 150 fs and the onset of a saturated velocity on a time scale of 1 ps, have been observed in the experiments. The time-dependent electric field has also been measured. It is found that both space-charge screening and terahertz radiation contribute to the collapse of the applied electric field at high carrier densities. Under such circumstances, transport and electric field dynamics are strongly coupled. An energy overshoot due to the field collapse coupled with strong electron-LO phonon scattering on a time scale of 200 fs is demonstrated. >

Femtosecond dynamics of semiconductor-microcavity polaritons in the nonlinear regime

We have investigated novel femtosecond dynamics of cavity-polaritons in a semiconductor quantum microcavity. When the cavity-polaritons are excited with a strong resonant pump in the nonlinear regime, we observe a reduction of cavity-polariton normal-mode splitting (vacuum Rabi splitting) due to saturation of the excitonic transition. By time-resolving the vacuum Rabi splitting, we observe novel properties of cavity-polaritons, including in-plane momentum relaxation associated with inhomogeneous broadening, and the absence of exciton scattering when the superposition of the cavity-polariton modes corresponds to the photon mode. This coherent dynamics is compared with the off-resonance pump case. In addition, we report no evidence of excitation of higher levels (n ≥ 1) of the Jaynes-Cummings model.

Coherent and Incoherent Dynamics of Excitons in Semiconductor Microcavities(

SummaryWe have investigated the dynamics of impulsively excited planar microcavities in the strongly couple regime. With resonant, coherent excitation, the emitted light shows vacuum-Rabi oscillations and a lifetime corresponding to twice the cavity lifetime. As the light intensity is increased, the exciton bleaching leads to reduced normal-mode splitting. The role of interface disorder on the dynamic splitting is discussed. Coherence transfer in exciton-exciton scattering is observed. Off-resonant excitation leads to long lifetimes limited by scattering into the radiatively coupled states of the exciton-cavity system.

Ultrafast spectroscopy of carriers and excitons in semiconductor microcavities

Abstract Experiments probing both the linear and nonlinear response of strongly coupled GaAs/ A1GaAs microcavities using femtosecond spectroscopy are described. Vacuum-Rabi oscillations are observed following resonant coherent impulsive excitation, with a decay time equal to twice the cavity lifetime as expected. Off-resonant excitation results in a long (≈600 ps) decay, resulting from the slow scattering of excitons into k≈0 states, and thermalized luminescence. In the nonlinear response, a dynamic reduction in the normal-mode splitting is observed. In nonresonant excitation, this is followed by gain-switched lasing.

Coherence Transfer in Exciton-Exciton Scattering in a Semiconductor Microcavity

We describe recent evidence which indicates how scattering of weakly localized exciton-polaritons gives rise to normally-directed coherent emission from an obliquely excited planar microcavity.