Abstract

Energetic ultrafast pulses at short wavelength are of interest as they have applications to time-domain studies of atoms, molecules, solids, and processes of biological interest,^1–4 micromachining, and the efficient generation of still shorter wavelength light. In recent work.⁵ we have shown that pulses from Ti:sapphire amplifiers may be converted to the UV through four-wave mixing with the second-harmonic in gas-filled hollow- core fibers. The waveguide geometry gives a long interaction length at high intensity without any focusing phase shift. Phase-matching is achieved through a balance of modal dispersion with the pressure-dependent dispersion of the gas. The nonresonant nature of this phase-matching process gives a wide phase-matching bandwidth with little temporal walkoff: pulses at 270 nm as short as 8 fs have been generated with this technique.⁶ The highest efficiency (up to 40% of the 400 nm pump, several-μJ output) is observed for the sum-and difference-frequency mixing process <ω_sig = 2ω_pump - (ω_idler since for this process all participating beams are in the lowest-order (near-Gaussian) spatial mode.

© 2002 Optical Society of America