High-order harmonic generation in the water window from mid-IR laser sources

We investigate the harmonic response of neon atoms to mid-IR laser fields (2000-3000 nm) using a single active electron (SAE) model and the fully ab initio all-electron R matrix with time dependence (RMT) method. The laser peak intensity and wavelength are varied to find suitable parameters for high-harmonic imaging in the water window. Comparison of the SAE and RMT results shows qualitative agreement between them as well as parameters such as the cutoff frequency predicted by the classical three-step model. However, there are significant differences in the details, particularly in the predicted conversion efficiency. These details indicate the possible importance of multielectron effects, as well as a strong sensitivity of quantitative predictions on specific aspects of the numerical model.