Dielectric response of electron-hole systems. Nondegenerate case and quantum corrections.

Analytical results for the dielectric function in RPA are derived for three-, two-, and one-dimensional semiconductors in the weakly-degenerate limit. Based on this limit, quantum corrections are derived. Further attention is devoted to systems with linear carrier dispersion and the resulting Dirac-cone physics.

Rydberg Excitons in the Presence of an Ultralow-Density Electron-Hole Plasma.

We study the Rydberg exciton absorption of Cu_{2}O in the presence of free carriers injected by above-band-gap illumination. Already at plasma densities ρ_{EH} below one hundredth electron-hole pair per µm^{3}, exciton lines are bleached, starting from the highest observed principal quantum number, while their energies remain constant. Simultaneously, the band gap decreases by correlation effects with the plasma. An exciton line loses oscillator strength when the band gap approaches its energy, vanishing completely at the crossing point. Adapting a plasma-physics description, we describe the observations by an effective Bohr radius that increases with rising plasma density, reflecting the Coulomb interaction screening by the plasma.

Collisional absorption in aluminum.

The interaction of ultrashort laser pulses with matter is a topic of growing interest. In particular, recent developments on free-electron lasers have opened an unexplored field in which many interesting physical phenomena are to be expected. Since hydrodynamic descriptions of the interaction process need a microscopic "input," a quantum statistical theory of energy absorption by matter is required. We present a kinetic theory of collisional absorption in dense plasmas and analyze the electron-ion collision frequency in warm dense aluminum in dependence on laser frequency and temperature.