Generation of high-order sum and difference frequencies by adding an intense parallel- and perpendicular-polarized infrared laser field

We demonstrate both efficient control of polarizations and high tunability of high-order sum and difference frequencies generated by adding an intense parallel- and perpendicular-polarized infrared laser field. When 805 nm pulses from a Ti:sapphire laser system and 1300 nm pulses from an optical parametric amplifier (OPA) are combined with perpendicular polarizations, the sum frequencies with two or four OPA photons are generated stronger than those with one or three OPA photons. This observation directly reflects the difference in their polarizations of the generated sum frequencies. Sum frequencies absorbing up to eight OPA photons are also observed for the parallel polarizations. Our observations are successfully reproduced by the theoretical calculations with the Lewenstein model including a weighting factor.