Successive high-order harmonic generation in hollow fibres

The method for phase matching of successive high-order harmonic generation in gas-filled hollow fibres is proposed. Successive harmonic generation all ows the energy of optical harmonics to be increased as compared with the di rect harmonic-generation process. With an appropriate choice of the type an d the pressure of the gas filling the fibre, parameters of the fibre, wavel ength of pump radiation, and waveguide modes, the phase-matching conditions can be simultaneously satisfied for all the steps of successive nonlinear optical high-order harmonic generation. Under these conditions, a gas-fille d hollow fibre may serve as an efficient two-colour source of coherent shor t-wavelength radiation.