Abstract

An ideal post compression arrangement for ultrafast laser systems introduces a strong, spatially homogeneous spectral broadening with high transmission. In a real setup however, there is always a trade-off between these figures of merit. The most frequently used post compression scheme uses self-phase modulation (SPM) in noble-gas-filled hollow fibers [1]. Here the spectral broadening is proportional to the accumulated nonlinear phase shift, the so called B-integral $(B=2\pi /{\lambda }_0{\displaystyle {\int }_0^L{n}_{2}Idz)}$. A too high intensity or nonlinear refractive index would however compromise the high transmission and good spectral homogeneity through self-focusing and photo-ionization [2]. Therefore the most favourable way to achieve strong spectral broadening in a well-controlled manner is to use long interaction length. By the use of the standard rigid hollow fibers, however the practical length is limited to about one meter mainly by waveguide losses of an imperfectly straight fiber. As a consequence, the maximum achievable spectral broadening factor is typically in the range of 4 to 8.

© 2011 Optical Society of America