Excimer Laser Pumped by an Intense, High-Energy Heavy-Ion Beam

High-energy heavy ions are an ideal tool to generate homogeneously excited, extended volumes of nonthermal plasmas. Here, the high-energy loss ($dE/dx$) and absolute power deposition of heavy ions interacting with matter has been used to pump an ultraviolet laser. A pulsed $70\mathrm{MeV}/u$ ${}^{238}\mathrm{U}$ beam with up to $2.5\times {10}^9$ particles in $\sim 100\mathrm{ns}$ beam bunches was stopped in a 1.2 m long laser cell filled with a 1.6 bar $\mathrm{Ar}\mathrm{\text{−}}\mathrm{Kr}\mathrm{\text{−}}{\mathrm{F}}_2$ mixture (typically $50\%:49.9\%:0.1\%$). Laser effect on the 248 nm ${\mathrm{KrF}}^{*}$ excimer transition is clearly demonstrated.

Figure 1

Demonstration of laser effect. The laser line at 248 nm appears in the emission along the laser axis as soon as the laser threshold is reached [lower spectrum (b), pumped with $1.3\times {10}^9\mathrm{\text{particles}}/\mathrm{\text{pulse}}$], whereas this line is completely absent below threshold [top spectrum (a), pumped with $0.98\times {10}^9\mathrm{\text{particles}}/\mathrm{\text{pulse}}$]. The broadband feature around 400 nm is due to ${\mathrm{Kr}}_2\mathrm{F}$ emission [13]. The narrow spikes are artefacts in the CCD detector of the spectrograph due to the background of hard radiation at the experimental area.

Figure 2

Demonstration of the threshold behavior of the laser.

Figure 3

Time structure of laser emission (a), spontaneous emission (b) and ion-beam pulse (c). The time structure of the ion-beam intensity was measured with an inductive current probe.