We characterize and control the harmonic emission in the spectral and spatial domains in order to define in which conditions the harmonic radiation can be a high-quality seed for soft x-ray and x-ray free-electron lasers. The length of the gas cell, where harmonics are generated, was optimized and the energy per pulse was determined in absolute value with a calibrated x-ray photodiode. The beam spatial profile was measured and, in some conditions, a very collimated beam with a half-angle divergence below 1 mrad could be obtained. We also show that increasing the intensity of the fundamental laser field leads to a considerable broadening of the bandwidth of the harmonic radiation, allowing us to cover a large spectral range. This effect is due to fundamental reshaping leading to an efficient phase matching of both short- and long-trajectory contributions. © 2009 The American Physical Society.
Publication Source (Journal or Book title)
Physical Review A - Atomic, Molecular, and Optical Physics
He, X., Miranda, M., Schwenke, J., Guilbaud, O., Ruchon, T., Heyl, C., Georgadiou, E., Rakowski, R., Persson, A., Gaarde, M., & L'Huillier, A. (2009). Spatial and spectral properties of the high-order harmonic emission in argon for seeding applications. Physical Review A - Atomic, Molecular, and Optical Physics, 79 (6) https://doi.org/10.1103/PhysRevA.79.063829