Highly advanced high harmonic coherent soft x-ray laser sources towards a water window region using laser-ablated solid target plasma

We have demonstrated the generation of high harmonics (HHs) by using a laser-ablation plume. As a quite novel phenomenon, a single harmonic enhancement has obtained by using laser-ablation plumes with a strong oscillator strength transition material. We attribute the strong enhancement of single harmonic to multiphoton resonance with a strong radiative transition of the ion. For extending cut off energy of HH, we have observed the extension of the cut off energy in HHG by using the doubly charged ions. This scheme looks like very much prospective to explore water window region.