Fig. 2.
Full phase matching of HHG. (A) Theoretical predictions for scaling of the phase matching cutoffs in Ar, Ne, and He gases, showing that full-phase matching of HHG emission can extend into the multi-keV X-ray region. (B) Experimentally, phase-matched emission (linear intensity scale) extends to 50 eV in Ar for 0.8-μm driving lasers. (C–E) Experimental data verifying significant extension of the phase matching cutoffs as λL increased from 0.8 to 1.3 μm in Ar (C), Ne (D), and He (E). In He, phase matching extends into the water window. (Above B–E, the filter transmission curves of the filters used to eliminate the driving laser light are shown.)