Generation of the attosecond extreme ultraviolet supercontinuum by a polarization gating

We report the first demonstration of extreme ultraviolet (XUV) supercontinuum generation in the plateau region of the high-order harmonic spectrum indicative of a single attosecond pulse. It was accomplished by combining the generation of sub-10 fs laser pulses with the polarization gating of high harmonic generation. When an 8 fs pulse centred at 750 nm was split and delayed with a quartz plate and then recombined with a quarter waveplate, a laser pulse was created whose polarization varied rapidly from circular to linear and back to circular. The near-linearly polarized portion of the resultant pulse was only 1.3 fs long, which was much shorter than the laser pulse duration. Since the high-order harmonic generation process is susceptible to the ellipticity of the driving field, the pulse with a time-dependent ellipticity behaved like a half-cycle linearly polarized pulse for generating XUV radiation. By exciting argon gas with the pulse, a supercontinuum that covered 25–45 nm was produced, which corresponds to an estimated single 200 as pulse. Acknowledgments This work is supported by the Division of Chemical Sciences, Office of Basic Energy Sciences, US Department of Energy. The authors acknowledge Dr Chun Wang and Eric Moon for assistance. We also thank Dr Philip Heimann at Lawrence Berkeley National Laboratory for loaning us the X-ray spectrometer. The Kansas Light Source was built partially with the support of a Major Research Instrumentation (MRI) grant from National Science Foundation awarded to Dr C.L. Cocke and Dr B. DePaola.