Sj. Vanenk et al., CALCULATION OF CHI((3)) IN HE FOR 25EV PHOTONS, Journal of physics. B, Atomic molecular and optical physics, 28(15), 1995, pp. 3453-3459
We calculate the third-order susceptibility in He, for photon energies
around 25 eV in the single-electron approximation. The results give a
calibration of the magnitude and feasibility of nonlinear processes u
sing short-wavelength radiation.