Hollow-core photonic-crystal fibers are shown to allow propagation and nonlinear-optical frequency conversion of high-intensity ultrashort laser pulses in the regime of isolated guided modes confined in the hollow gas-filled fiber core. With a specially designed dispersion of such modes, the $3\omega =2\omega +2\omega -\omega$ four-wave mixing of fundamental $\left(\omega \right)$ and second-harmonic $\left(2\omega \right)$ sub-100-$\mathrm{TW}∕{\mathrm{cm}}^2$ femtosecond pulses of a Cr:forsterite laser can be phase matched in a hollow photonic-crystal fiber within a spectral band of more than 10 nm, resulting in the efficient generation of femtosecond pulses in a well-resolved higher-order air-guided mode of 417-nm radiation.

• Received 8 March 2004

DOI:https://doi.org/10.1103/PhysRevE.70.066625