Generation of intense continuum extreme-ultraviolet radiation by many-cycle laser fields

Continuing efforts in ultrashort pulse engineering have recently led to the breakthroughs of the generation of attosecond (10(-18) s) pulse trains(1-7) and isolated pulses(8-11). Although trains of multiple pulses can be generated through the interaction of many-optical-cycle pulses with gases-a process that has led to intense extreme-ultraviolet emission(3-5)-the generation of isolated high-intensity pulses, which requires few-cycle driving pulses, remains a challenge. Here, we report a vital step towards the generation of such pulses, the production of broad continuum extreme-ultraviolet emission using a high-intensity, many-cycle, infrared pulsed laser, through the interferometric modulation of the ellipticity of 50-fs-long driving pulses. The increasing availability of high-power many-cycle lasers and their potential use in the construction of intense attosecond radiation-with either gas or solid-surface targets(12)-offer exciting opportunities for multiphoton extreme-ultraviolet-pump -extreme-ultraviolet-probe studies of laser-matter and laser-plasma interactions.