HIGH-ORDER TUNABLE SUM AND DIFFERENCE-FREQUENCY MIXING IN THE XUV REGION

We present a study of tunable high-order sum and difference frequency mixing in the 7-70 eV range, in xenon, argon and neon. We mix the ligh t from a terawatt, subpicosecond titanium-sapphire laser and that from a tunable optical parametric generator. The radiation generated throu gh mixing processes involves absorption or emission of one or Mo photo ns from the weak tunable source. The relative strengths of the sum and difference frequency processes depend strongly on the wavelength rang e of the generated radiation. The sum frequency processes are stronger at low photon energies in xenon, whereas the difference frequency pro cesses dominate at high photon energies, in neon, being almost compara ble to harmonic generation.