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The output pulses of a commercial high-power femtosecond fiber laser oramplifier are typically around 300-500 fs with a wavelength around 1030 nm and10s of $\mu$J pulse energy. Here we present a numerical study of cascadedquadratic soliton compression of such pulses in LiNbO$_3$ using a type I phasematching configuration. We find that because of competing cubic materialnonlinearities compression can only occur in the nonstationary regime, wheregroup-velocity mismatch induced Raman-like nonlocal effects prevent compressionto below 100 fs. However, the strong group velocity dispersion implies that thepulses can achieve moderate compression to sub-130 fs duration in availablecrystal lengths. Most of the pulse energy is conserved because the compressionis moderate. The effects of diffraction and spatial walk-off is addressed, andin particular the latter could become an issue when compressing in such longcrystals (around 10 cm long). We finally show that the second harmonic containsa short pulse locked to the pump and a long multi-ps red-shifted detrimentalcomponent. The latter is caused by the nonlocal effects in the nonstationaryregime, but because it is strongly red-shifted to a position that can bepredicted, we show that it can be removed using a bandpass filter, leaving asub-100 fs visible component at $\lambda=515$ nm with excellent pulse quality.

On type I cascaded quadratic soliton compression in lithium niobate: Compressing femtosecond pulses from high-power fiber lasers