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 allows the energy of optical harmonics to be increased as compared with the direct harmonic-generation process. With an appropriate choice of the type and the pressure of the gas filling the fibre, parameters of the fibre, wavelength 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-filled hollow fibre may serve as an efficient two-colour source of coherent short-wavelength radiation.