  We investigate the harmonic response of neon atoms to mid-IR laser fields
(2000-3000nm) 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
multi-electron effects, as well as a strong sensitivity of quantitative
predictions on specific aspects of the numerical model.
