Light pulses from a femtosecond laser can be coherently upconverted to generate light in the soft x‑ray region of the spectrum using the technique of high-order harmonic generation. Advances in laser technology, combined with a better understanding of the high harmonic process [1], have made it possible to implement an ultrashort-pulse source of ionizing radiation with flux sufficient for a variety of application experiments [2] and with unique capabilities. For example, recently, we have done the first direct time-resolved studies of molecular fragmentation resulting from ionization [3], and have probed the angle-dependent photoionization cross section of laser-aligned molecules. The high-order harmonic generation process itself also can be used to probe molecular structure [4]. In this talk I will give an overview of experiments in this area done in our group, and will discuss the technology and future prospects for tabletop-scale ultrafast x-ray sources.

[1] H. Kapteyn, O. Cohen, I. Christov, and M. Murnane, "Harnessing attosecond science in the quest for coherent X-rays," Science 317(5839), 775-778 (2007).
[2] R.L. Sandberg, C.Y. Song, P.W. Wachulak, D.A. Raymondson, A. Paul, B. Amirbekian, E. Lee, A. E. Sakdinawat, C. La-O-Vorakiat, M.C. Marconi, C.S. Menoni, M.M. Murnane, J.J. Rocca, H. C. Kapteyn, and J.W. Miao, "High numerical aperture tabletop soft x-ray diffraction microscopy with 70‑nm resolution," Proceedings of the National Academy of Sciences of the USA 105(1), 24‑27 (2008).
[3] E. Gagnon, P. Ranitovic, A. Paul, C.L. Cocke, M.M. Murnane, H.C. Kapteyn, and A.S. Sandhu, "Soft x‑ray driven femtosecond molecular dynamics," Science 317(5843), 1374-1378 (2007).
[4] X. Zhou, R. Lock, W. Li, N. Wagner, M.M. Murnane, and H.C. Kapteyn, "Molecular Recollision Interferometry in High Harmonic Generation," Phys. Rev. Lett. 100, 073902 (2008).

ANL Physics Division Colloquium Schedule