Wavelength scaling of high-order harmonic yield from an optically prepared excited state atom

The wavelength scaling law for the yield of high-order harmonic emission is theoretically examined for excited state atoms that are optically prepared by simultaneously exposing to an extreme ultraviolet pulse at the resonant wavelength and an infrared pulse at a variable wavelength in the range of 0.8-2.4 μm. Numerical simulations are performed based on the three-dimensional time-dependent Schrödinger equation for Ne and H. We confirm that the harmonic yield follows a λ^-(4-6) scaling with the single fundamental driving laser pulse, whereas for the optically prepared excited state atoms, a λ^-(2-3) scaling for the harmonic yield is revealed.