PHASE-MATCHING FOR LARGE-SCALE FREQUENCY UP-CONVERSION IN PLASMA

We consider phase matching in the generation of very short-wavelength coherent radiation by nonlinear frequency upconversion in plasma and s uggest some ways to improve phase matching in high-order harmonic gene ration. We obtain what are to our knowledge the first simple analytica l expressions for a phase-matching factor in multiphoton mixing of an arbitrary order and demonstrate theoretically that high-order differen ce-frequency mixing in plasma could be, owing to its potential for pha se-matching optimization, a more promising method of large-scale frequ ency upconversion than high-order harmonic generation.