We observe shock waves with velocity 2.5×106 cm/sec generated by the interaction of a nanosecond CO2 laser at an intensity of 3×1014 W/cm2 with 12–40‐μm‐thick aluminum foils. It is proposed that these shock waves are not generated by thermal ablation but rather by hot electron heating and explosion of a layer of Al several microns thick adjacent to the target surface. Shock pressures produced by this process are comparable to the highest pressures yet observed by conventional laser driven thermal ablation.

Generation of shock waves by hot electron explosions driven by a CO2 laser

An analytic hydrodynamic model for the formation and decay of strong shock waves (0.1–10 TPa) is derived in this paper by using self‐consistent and well‐defined assumptions. A trapezoidal pressure profile as a function of time applied to the target surface is used as the initial condition. This model permits the calculation of the pressure, velocity, and acceleration of the shock front, as well as the calculation of the pressure gradient immediately behind the shock front, as functions of time and position. This model is applied to laser‐generated shock waves with maximum intensities of 5×1013 and 5×1014 W/cm2. Good agreement with previous computer simulations of solid–laser interaction is obtained.

An analytical model for creation and decay of strong shock waves caused by a trapezoidal laser pulse

The recently obtained closed-form representation of the non-resonant thermonuclear reaction rate by a generalized hypergeometric function (Meijer's G-function) is used for a fusion yield calculation. A simplified physical model for the hydrodynamical processes in a fusion plasma compressed and heated by a laser-driven spherical shock wave permits calculation of the released fusion energy by integrating the thermonuclear reaction rate over the temperature. With the aid of the closed-form representation of the reaction rate this fusion energy production integral is approximation-free evaluated. After computing numerical factors, the approximate representation of the fusion energy yield given until now in the literature is compared with the more accurate ones obtained in this paper, and the apparent discrepancies are discussed.

Analytical representation of the thermonuclear reaction rate and fusion energy production in a spherical plasma shock wave

This report will give an introduction to the X-line emission processes in laser-generated plasmas according to a plasma physical point of view. After a short discussion of the experimental results using laser pulses in the range of ≲ 10 J and irreadiances of 1 to 100 MW/cm2 and of first conclusions about the temperature scaling and the dependence of the emission concerning the atomic number of the target material some models of laser-generated plasmas are analysed. The simple hot-spot model neglects any hydrodynamics and only solves for the rate equations. We discuss the underlying collisional-radiative model and evaluate the numerical results of a more complete model for the spatial and temporal plasma evolution including the hydrodynamics. The applications of such plasmas as small, strong, short sources of X-rays in the keV range is discussed with regard to the lithographic replication of sub-μm structures and to the EXAFS spectroscopy. Laser-generated plasmas are compared with conventional X-ray tubes (with rotating anode) and with synchrotrons. The question of amplified spontaneous emission in the XUV range (superradicant X-ray sources) is only shortly touched upon. In conclusion some comments are given to the recoil momentum effects of the ablating plasma on the target are given (rocket model).

M.H. Key

Papers

Physics at very high pressures with laser-driven shock waves