Solid-Core Fiber Spectral Broadening at Its Limits

Broadband optical spectra are employed in ultrafast time-resolved studies, seeding of tunable parametric amplifiers, and selectively addressing transitions in absorption spectroscopy. A strong extension of spectral bandwidth is commonly achieved in nonlinear fiber by means of self-phase modulation. In terms of energy scalability and achievable bandwidth, the method is, however, limited by the damage threshold of the core material. Here, we study spectral broadening in four different single-mode normal dispersive photonic crystal fibers length of 8-10 cm. They are pumped by a thin-disk oscillator emitting 250 fs pulses at peak powers close to the critical power of silica. We demonstrate mode-field diameter-dependent broadening factors from 19 to 51, which are obtained at power spectral densities from 200 to 5 mW/nm. We explain the results by a relation between peak power and broadening factor. This will serve as a fiber selection guideline transferable to lasers emitting at wavelengths different from 1030 nm. In addition, we examine to which extend prechirp leads to energy scalability of spectral broadening in solid-core fiber. By contrast to previous reports, we point out that the applicability of the technique is strongly limited through the requirement of bell-shaped input pulses and the pulse duration dependent material damage threshold.