Mechanism of hollow-core-fiber infrared-supercontinuum compression with bulk material

We numerically investigate the pulse compression mechanism in the infrared spectral range based on the successive action of nonlinear pulse propagation in a hollow core fiber followed by linear propagation through bulk material. We found an excellent agreement of simulated pulse properties with experimental results at 1.8 mu m in the two optical cycle regime close to the Fourier limit. In particular the spectral phase asymmetry attributable to self steepening combined with self phase modulation is a necessary prerequisite for subsequent compensation by the phase introduced by glass material in the anomalous dispersion regime. The excellent agreement of the model enabled simulating pressure and wavelength tunability of sub two cycles in the range from 1.5 to 4 mu m with this cost efficient and robust approach.