Compression of megawatt femtosecond laser pulses using a large-mode-area all-silica photonic band-gap fiber

This paper show that an all-solid photonic band-gap fiber (PBGF) with a large mode area offers interesting new options for the compression of high-peak power laser pulses. Even in the class of large-mode-area fibers, dispersion of PBGFs can be efficiently tailored by tuning photonic band gaps of the fiber cladding. The fiber provides a low-loss transmission within the fundamental photonic band gap of its cladding from approximately 930 to 1300 nm. Laser pulses experienced a significant spectral broadening as a result of nonlinear-optical processes inside the fiber, with the spectrum of light pulses transmitted through fiber covering, roughly, the entire transmission band of the PBGF. Spectral-temporal maps of ultrashort light pulses were measured by cross-correlation frequency resolved optical gating (XFROG) with a 800-nm, 70-fs output of a solid laser used as a reference pulse. A typical XFROG trace of a laser pulse transmitted through a 22-cm piece of PBGF, suggests that group velocity dispersion of the PBGF vanishes at approximately 1200 nm and indicates that a chirp acquired by the light pulse at the fiber output is mainly due to the normal dispersion of the fiber. With a prism compressor designed to compensate for this chirp, light pulses with a pulse width of about 60 fs and an energy of 0.35 muJ were produced. XFROG traces of compressed pulses suggest that even shorter pulse widths can be achieved with an accurate compensation of high-order phase shifts.