100-nm tunable femtosecond Cr:LiSAF laser mode locked with a broadband saturable Bragg reflector

We report broad tunability of a femtosecond (fs) diode-pumped Cr:LiSAF laser mode-locked with a broadband saturable Bragg reflector (SBR). The SBR had seven pairs of AlxOy(n∼1.5) and Al0.17Ga0.83As(n∼3.5) layers in its Bragg stack, enabling a 250 nm reflectivity bandwidth around 850 nm. A 6-nm-thick strained In0.15Ga0.85As quantum well placed between Al0.17Ga0.83As cladding layers was used as a broadband saturable absorber in the 800–920 nm wavelength range. The laser was pumped by 6 single mode diodes—four at 640 nn and two at 660 nm. Mode locking was self-starting and fs pulses could be continuously tuned from 800 nm to 905 nm by an intracavity birefringent filter with an out-of-plane optic axis. The pulse widths varied from 70 fs to 255 fs as the laser was tuned. The laser had an 85.5 MHz repetition rate and the output power varied from 80 mW to 180 mW with tuning.