An intense continuously tunable 20-fs source is demonstrated for the region between 370 and 430 nm with pulse energies of as much as 20 mu J. By use of high-power frequency-doubled pulses from a 32-fs 1-kHz Ti:sapphire laser system a blue continuum is produced in an Ar-filled hollow fiber. After compression with dispersive delay lines the resulting pulses are analyzed by use of the self-diffraction frequency-resolved optical gating technique. (C) 1997 Optical Society of America.