High-power widely tunable sub-20 fs Gaussian laser pulses for ultrafast nonlinear spectroscopy.

We demonstrate the generation of widely tunable sub-20 fs Gaussian-shaped laser pulses using a grating-based 4-f pulse shaper and a liquid crystal spatial light modulator. Our pump source is an Yb:KGW solitary mode-locked oscillator at 44 MHz repetition rate which is coupled into a large mode area microstructured fiber to generate a broad spectrum from below 900 nm to above 1150 nm. These pulses are precompressed by a prism sequence and subsequently sent into the pulse shaper. We use the multiphoton intrapulse interference phase scan (MIIPS) for phase shaping and iterative amplitude optimization to achieve Gaussian-like tunable sub-20 fs pulses with output powers of up to 142 mW as well as nontunable pulses with 310 mW output power as short as 11.5 fs.