The resistivity of nearly solid-density Al was measured as a function of temperature over 4 orders of magnitude above ambient by observing the self-reflection of an intense, <0.5 psec, 308-nm light pulse incident on a planar Al target. As an increasing function of electron temperature, the resistivity is observed initially to increase, reach a maximum which is relatively constant over an extended temperature range, and then decrease at the highest temperatures. The broad maximum is interpreted as "resistivity saturation," a condition in which the mean free path of the conduction electrons reaches a minimum value as a function of temperature, regardless of the extent of any further disorder in the material.PACS numbers: 72.15.Cz, 52.25.Fi, 78.47.+p We report the first experimental study of the electrical resistivity of a solid-density material, in this case a simple Drude metal, over an extended range (4 orders of magnitude) of elevated temperature with little or no change in its density. The results show three general regions of the dependence of the resistivity on the temperature: Initially, the resistivity increases with increasing temperatures, reaching a relatively constant value that extends over a wide temperature range, and then it decreases as the temperature is further increased. We argue that these regions reflect differing mechanisms controlling the mean free path of the conduction electrons in different temperature ranges. In particular, the region of maximum resistivity is a result of "resistivity saturation," a condition in which the electron mean free path reaches a minimum value, independent of the degree of material disorder.The ability to study the resistivity of a well characterized solid-density material over a great range of elevated temperatures was made possible here by the use of ultrashort (<0.5 psec), relatively high-energy (0-5 mJ) laser pulses. The self-reflection of a laser pulse, focused onto a smooth target at fixed pulsewidth and spot size, was monitored over 4 orders of magnitude in energy. Frequency shifts of the reflected light were also recorded, and as discussed in detail below, these frequency shifts are shown to arise directly from the expansion velocity of the solid-vacuum interface. From the dependence of the interface velocity upon the laser intensity, we were able to determine the electron temperature and degree of interface expansion for each recorded value of the reflectivity. This information is sufficient to determine the resistivity of solid-density Al as a function of temperature up to 10 6 K.It is important to differentiate between the type of heating-reflectivity experiment reported here and those conducted with high-energy (> 100 mJ), long-duration ( > 50 psec) pulses. In the latter, the majority of the en-ergy is absorbed not by the dense target, but rather by the material expanding away from the interface over a scale of many wavelengths. Detailed hydrodynamic calculations are usually required to analyze the data from this type of experiment, l and no simpl...
Marshall Rosenbluth's extensive contributions included seminal analysis of the physics of the laser-plasma interaction and review and advocacy of the inertial fusion program. Over the last decade he avidly followed the efforts of many scientists around the world who have studied Fast Ignition, an alternate form of inertial fusion. In this scheme, the fuel is first compressed by a conventional inertial confinement fusion driver and then ignited by a short ͑ϳ10 ps͒ pulse, high-power laser. Due to technological advances, such short-pulse lasers can focus power equivalent to that produced by the hydrodynamic stagnation of conventional inertial fusion capsules. This review will discuss the ignition requirements and gain curves starting from simple models and then describe how these are modified, as more detailed physics understanding is included. The critical design issues revolve around two questions: How can the compressed fuel be efficiently assembled? And how can power from the driver be delivered efficiently to the ignition region? Schemes to shorten the distance between the critical surface where the ignitor laser energy is nominally deposited and the ignition region will de discussed. The current status of Fast Ignition research is compared with our requirements for success. Future research directions will also be outlined.
The version of Fig. 4 that was inadvertently included in the original publication did not show the results of Monte Carlo modeling referred to in the caption and the text. The correct figure and its caption are shown below. This does not affect the conclusions of the article. FIG. 4. Integrated K ␣ fluorescence energy versus mass fraction of Cu fluor in Al/ Cu/ Al targets. The front Al layer varied from zero to 500 m, the Cu layer was 20-25 m. The back Al layer was 100 m for the four ϫ points, and 40 m for the ϩ, 10-20 m otherwise. The open symbols show the predictions from Monte Carlo modeling with an arbitrary relative normalization. The back Al layer in the model is either 16 m ͑square͒ or 100 m ͑triangle͒.
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