A quantitative analysis of carrier-carrier scattering and optical dephasing in semiconductors is presented and results are given for quasiequilibrium situations and for the relaxation of a kinetic hole in a quasithermal carrier distribution.The calculations involve direct numerical integration of the Boltzmann equation for carrier-carrier scattering in the Born approximation.The screening of the Coulomb interaction is treated consistently in the fully dynamical random-phase approximation. Carrier relaxation rates are extracted from the Boltzmann-equation solution and a quantitative test of the relaxation-time approximation for situations near thermal quasiequilibrium is performed. The parametric dependence of carrier-collision rates and dephasing on plasma density, temperature, and electron and hole masses is discussed and analyzed in terms of phase-space blocking and screening.

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International audienceHigh-power light-emitting diodes (LEDs) today are twice as powerful as four years ago while meantime their price has been divided by 4 making them promising sources for laser pumping. However, their irradiance still falls short by one order of magnitude of what is needed to efficiently pump solid-state lasers. We demonstrate that an LED-pumped Ce:YAG luminescent concentrator (LC) can increase the irradiance of blue LEDs by a factor of 10, with an optical efficiency of 25%, making them much more suitable to pump solid-state lasers. In our demonstration , we used 100 Hz pulsed LEDs emitting 190 W∕cm 2 at 430 nm to illuminate a Ce:YAG LC, leading to an output irra-diance of 1830 W∕cm 2. The LC is used to pump a Nd:YVO 4 laser producing 360 μJ at 1064 nm, corresponding to an optical efficiency of 2.2% with respect to the LC. LED-pumped lumi-nescent concentrators pave the way for high-power, low-cost, solid-state lasers

A coupled set of equations for carrier distributions and stimulated emission in a semiconductor laser is presented, based on a nonequilibrium Green s-function formulation. Carrier momentum-dependent dephasing caused by carrier-carrier scattering and frequency-dependent optical gain are shown to govern the interplay between carrier relaxation and stimulated recombination. Ignoring the interband Coulomb interaction, the coupled system of equations for the carrier distribution functions and the optical gain is solved self-consistently for a single-mode short-cavity semiconductor laser under steady-state operation conditions. Numerical results show spectral and kinetic hole burning as well as nonlinear gain saturation.PACS number(s): 42.55.Px, 42.65. -k