Abstract
We present new schemes for phase matching and quasi-phase matching extreme high-order harmonic generation. Using longer wavelength driving light at 1.3 ìm, we extend full phase matching of high harmonic generation in argon and neon to 100 and 200 eV respectively, well beyond the phase-matching limit for 0.8 ìm. Also, we show that multiple weak quasi-CW waves can induce phase modulated structures in the high-harmonic generation process that can be used for highly efficient quasi-phase matching.