CO2 Laser-Heated Plasmas for Electron-Collisionally Pumped XUV Laser Studies

We describe a series of experiments to characterize plasmas produced by moderate intensity (≈ 2x1013 W/cm2), nanosecond pulse, CO2 laser irradiation of planar targets using both line (150 μm x 7 mm) and spherical (1mm diam.) focussing optics. X-ray line and continuum diagnostics have been used to infer a heat front penetration of about 20 μgm/cm2 at temperatures of approximately 300 eV. We observe only minor differences between targets whose mass is small compared to the hot electron range and much more massive ones, indicating a poor efficiency for hot electron reflexing in thin targets. In the case of Cu targets, observations of L shell x-ray transitions from neon and fluorine-like ions show a similar ionization distribution to 1 μm laser produced plasmas in which gain has recently been demonstrated. The Ne-like Cu XX 3p-3s emission lines have been observed. A comparison of on-axis to off-axis spectra provides evidence for gain on these lines.