ULTRAFAST LASERS: Hollow waveguides compress high-energy ultrafast pulses

Noble-gas-filled hollow waveguides induce self-phase modulation in short optical pulses, spectrally broadening them to produce 10-fs pulses with energies as high as 240 µJ (see Laser Focus World, July 1996, p. 9). While single-mode optical fiber has previously been used to broaden pulses, nonlinear effects such as multiphoton ionization and self-focusing limited the technique to low-energy pulses. Experiments with the hollow-waveguide technique have shown no unwanted nonlinear effects for input energies up to 660 µJ; work is underway at Centro di Elettronica Quantistica e Strumentazione Elettronica (Milan, Italy) under the direction of Orazio Svelto to apply the technique to input energies on the order of millijoules.