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The attosecond nonlinear optics of bright coherent X-ray generation


The frequency doubling of laser light was one of the first new phenomena observed following the invention of the laser over 50 years ago. Since then, the quest to extend nonlinear optical upconversion to ever-shorter wavelengths has been a grand challenge in laser science. Two decades of research into high-order harmonic generation has recently uncovered several feasible routes for generating bright coherent X-ray beams using small-scale femtosecond lasers. The physics of this technique combines the microscopic attosecond science of atoms driven by intense laser fields with the macroscopic extreme nonlinear optics of phase matching, thus essentially realizing a coherent, tabletop version of the Roentgen X-ray tube.

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Figure 1: The microscopic single-atom physics of HHG.
Figure 2: Macroscopic phase-matching of HHG in the spatial domain.
Figure 3: Macroscopic phase-matching of HHG in the temporal domain.
Figure 4: Spatially coherent HHG emission for applications in imaging.
Figure 5: Phase matching of HHG using mid-infrared lasers.
Figure 6: Attosecond pulse generation.
Figure 7: QPM techniques for extreme nonlinear optics.


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The authors thank S. Backus of KMlabs and I. Christov of Sofia University. Several past students and postdocs also made critical contributions to the work discussed here, including A. Bahabad, R. Bartels, Z. Chang, O. Cohen, C. Durfee, E. Gibson, A. Lytle, J. Peatross, A. Rundquist, X. Zhang and J. Zhou. This work was funded by the National Science Foundation, a National Security Science and Engineering Faculty Fellowship, the US Department of Energy (DOE) and the DOE National Nuclear Security Agency.

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Correspondence to Henry C. Kapteyn.

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Henry C. Kapteyn and Margaret M. Murnane own a small laser company (KMLabs) that sells ultrafast lasers and EUV high-harmonic sources. Tenio Popmintchev owns a small consulting company (Coherent X-ray Group).

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Popmintchev, T., Chen, MC., Arpin, P. et al. The attosecond nonlinear optics of bright coherent X-ray generation. Nature Photon 4, 822–832 (2010).

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