New paper published in Physical Review A


XFROG spectrogram of compressed pulse

In the May 2010 issue we investigate the potential of using lithium niobate as nonlinear crystal for generating cascaded femtosecond solitons and achieving soliton compression of pulses from commercial femtosecond fiber laser amplifiers. This crystal has not been considered before due to its very high dispersion in the visible, but we show that a substantial cascaded nonlinearity can be achieved when pumping with Yb-based fiber lasers at the 1030 nm wavelength. This can compress multi-microjoule pulses towards 100 fs duration. The limit is set by the strong group-velocity mismatch in the crystal. A surprising result is that the large group-velocity dispersion in the crystal actually helps compressing the pulse within a realistic crystal length (app. 10 cm). The results are an important step towards realizing sub-100 fs pulses from fiber laser amplifiers.


The phase matching configuration is type I (different polarizations at the pump and the second-harmonic wavelengths), where lithium niobate has a medium strength nonlinearity. We envisage that the very large nonlinearity in a type 0 configuration (equal polarizations at the pump and harmonic wavelengths) can be helpful in achieving pulse compression towards the few-cycle regime, simply because the group-velocity mismatch problems can be avoided.


M. Bache and F. W. Wise
Type I cascaded quadratic soliton compression in lithium niobate: Compressing femtosecond pulses from high-power fiber lasers
Physical Review A 81, 053815 (2010)