Enhancement of x-ray yield from the Z-Beamlet laser for monochromatic backlighting by using a prepulse

Abstract

The Z-Beamlet Laser (ZBL) is capable of providing on-target energies of up to 1.5kJ at 527nm in up to four separate 0.3–1.5ns pulses during a 20ns window. ZBL is routinely used as a source of x rays for backlighting experiments on the Sandia Z facility, a 20MA, 100ns rise-time, pulsed-power driver for z-pinch plasma radiation sources. Most backlighting experiments use monochromatic crystal imaging diagnostics at 1865 or 6151eV. We present calibration data demonstrating that the use of a 0.3–0.6ns, ∼200J pulse, followed 2ns later by a 1.0ns, ∼1kJ pulse results in more than twice the x-ray yield at 6151eV (a He-like Mn emission line) compared to a single 1.0ns, ∼1kJ pulse. The first pulse creates a plasma (and few x rays) that expands and approaches the critical density for the laser when the second pulse arrives, creating a more efficient coupling of laser light to the plasma. A similar improvement was also noted for He-like Ni emission lines, suggesting that this simple technique scales to higher photon energies.