TY - JOUR AU - A. Lytle AU - X. Zhang AU - J. Peatross AU - Margaret Murnane AU - Henry Kapteyn AU - O. Cohen BT - Physical Review Letters DA - 2007-03 DO - 10.1103/PhysRevLett.98.123904 PY - 2007 T2 - Physical Review Letters TI - Probe of High-Order Harmonic Generation in a Hollow Waveguide Geometry using Counterpropagating Light VL - 98 SN - 0031-9007 ER -