%ALi, F.%ASheng, Z.%ALiu, Y.%AMeyer-ter-Vehn, J.%AMori, W.%ALu, W.%AZhang, J.%BJournal Name: Physical Review Letters; Journal Volume: 110; Journal Issue: 13 %D2013%IAmerican Physical Society %JJournal Name: Physical Review Letters; Journal Volume: 110; Journal Issue: 13 %K %MOSTI ID: 10008439 %PMedium: X %TDense Attosecond Electron Sheets from Laser Wakefields Using an Up-Ramp Density Transition %XNot Available %0Journal Article