Abstract
By focusing a high repetition rate (50kHz), compact, femtosecond laser system with low pulse energy (25μJ) using a tight- focusing geometry, we demonstrate fully phase matched high-order harmonic generation for the first time at very high repetition rates, resulting in EUV light with full spatial coherence. The result is a practical, single- box, coherent source useful for applications in metrology, ultrafast spectroscopy, imaging and microscopy. The soft x-ray flux can be improved further by increasing the laser pulse energy and/or repetition rate.© 2009 Optical Society of America.