A pump-probe Investigation of krypton droplet plasma formation in an intense laser field

Abstract

Summary form only given. Over the past several years, work ha progressed on a laser plasma-based source for extreme ultraviolet (EUV) lithography. The interaction of intense laser pulses with noble gas droplets produces EUV radiation with efficiencies (/spl sim/0.5% in the reflective optics bandwidth) comparable to those of solid targets, but with minimal debris generation. Workers at Sandia have shown high efficiency EUV generation from the interaction of 10-ns laser pulses with xenon droplets. However, it has been found that EUV generation from Kr droplets which are a few microns in diameter is most efficient for laser pulses which are /spl sim/300 ps in duration. In order to better understand the droplet disassembly dynamics, we have performed a pump-probe experiment using 1064-nm, 100-ps duration laser pulses. The first laser pulse heats the droplets, forming a plasma, and the second pulse serves as a heater probe for measuring the characteristic disassembly time of the Kr droplets. Using EUV and X-ray (> 1.5 keV) signals generated by the second pulse as diagnostics, the disassembly time is shown to be as long as several nanoseconds, depending on average droplet radius.