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.

Figure 1

Collision frequency of solid Al as a function of the temperature. The figure is taken from Ref. 13.

Figure 2

Ion-ion structure factor for aluminum at solid-state density, $\rho =2.7\mathrm{g}∕{\mathrm{cm}}^3$ (corresponding to an ion density of $n_i=6\times {10}^{22}{\mathrm{cm}}^{-3}$) from HNC calculations for several temperatures. The effective ion radius is chosen to be $r_0=0.054\mathrm{nm}$ $=1.05a_B$ (the radius of ${\mathrm{Al}}^{3+}$ ions in a crystal [31]).

Figure 3

Real part of the electron-ion collision frequency vs laser frequency for aluminum. System parameters: see Fig. 2. The result using the HNC static ion-ion structure factor is compared with the free-particle case.

Figure 4

Real part of the electron-ion collision frequency vs electron temperature for aluminum ($n_i=6\times {10}^{22}{\mathrm{cm}}^{-3}$, $T_i=T_e$) for two different laser wavelengths: (a) $\lambda =800\mathrm{nm}$, (b) $\lambda =32\mathrm{nm}$. The HNC result for $S_{ii}$ is compared with the free-particle case. In addition, the limiting case for high $T$ (Spitzer formula) is shown.

Figure 5

Real part of the electron-ion collision frequency vs laser frequency for aluminum at solid-state density and a temperature of $T={10}^6\mathrm{K}$ for several laser intensities.

Figure 6

Real part of the electron-ion collision frequency vs electron temperature for aluminum, $T_i=T_e$, for two different laser wavelengths: (a) $\lambda =800\mathrm{nm}$, (b) $\lambda =32\mathrm{nm}$, and several laser intensities. In addition, the limiting case for high $T$ (Spitzer formula) is shown.

Figure 7

Dynamic collision frequency vs electron temperature for aluminum, $T_i=T_e$. The narrow-dotted line denotes ${\nu }_{e\text{−}\mathrm{ph}}$ according to Eq. (36), the dash-dotted line corresponds to Eq. (16) of Ref. 14. The thick solid line denotes a connection of ${\nu }_{e\text{−}\mathrm{ph}}$ (36) and $\mathrm{Re}{\nu }_{ei}$ (33).