Beneficial effect of CH foam coating on x-ray emission from laser-irradiated high-Z material

Abstract

Laser-irradiated Au layer with CH foam coating is investigated numerically. It is found that when coated with under-critical density CH foam more thermal radiation is produced, while less radiation is produced when coated with over-critical density CH foam. The under-critical density CH foam coating, which is heated supersonically and volumetrically by lasers, hampers the expansion of high-Z plasma and helps increase the density and temperature of Au plasma in the radiation zone. It is a practical and simple way to increase the laser x-ray conversion efficiency of hohlraum by coated with low-Z foam of under-critical density. This idea is tested with an experiment in an analogous geometry. The line emission from laser-irradiated Ti layer coated with CH foam was measured, and the increment of x-ray when coated with under-critical density CH foam was found.

Enhanced x-ray emissions from Au-Gd mixture targets ablated by a high-power nanosecond laser

“…In these applications, the most desirable objective is to maximize the x-ray radiation intensity by choosing proper laser and target parameters. 7 Various methods, such as short wavelength, 8,9 and long pulse lasers, 10 high-Z material, 11 foam coating, 12 and low-density foam targets, 13 have been proved practically to achieve higher x-ray radiation from laser-produced plasmas.…”

Optimization of x-ray emission from under-critical CH foam coated gold targets by laser irradiation

“…Figure 5 presents the values of the density and electron temper ature in the center of the electron conduction zones, and the electron conduction zone lengths. It is reported that CH plasma can inhibit gold plasma expansion and increase plasma density and temperature in the electron conduction zone [20]. As shown in figure 5, the plasma density in the electron conduction zone increases as the CH foam thickness grows, which means more gold plasma expansion is inhibited with thicker CH foam.…”

“…When the thickness is 300 μm, the 10 mg cm −3 CH foam absorbs 9.7% of the incident laser energy, and the 25 mg cm −3 CH foam absorbs 80% of the incident laser energy. It is reported that CH plasma inhibits gold plasma expansion, which benefits the laser-to-x-ray CE [20]. However, the x-ray emission decays if a significant fraction of incident laser energy is absorbed in the CH plasma, which will be shown in the next section.…”

“…Additionally, the x-ray emission increases significantly with the CH foam coated gold target, and much stronger emission can be obtained at a later time in the laser duration (>0.5 ns). The reason is that higher plasma temperature and density are achieved in the radiation zone with the CH foam coated gold target [20]. Furthermore, the thicker CH foam coated gold target implies longer plasma decaying time as presented in figure 3, which suggests higher plasma temperature.…”

“…Recently, an under-critical CH foam coated high-Z target was proposed to increase the laser-to-x-ray CE [20]. The under-critical density CH foam, which is heated supersonically and volumetrically by lasers, inhibits the expansion of gold plasma and helps increase the density and temperature in the radiation zone.…”